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Movements of the white shark (Carcharodon carcharias) in the North Atlantic Ocean
Abstract
In the western North Atlantic, much of what is known about the movement ecology of the white shark Carcharodon carcharias is based on historical fisheries-dependent catch records, which portray a shelf-oriented species that moves north and south seasonally. In this study, we tagged 32 white sharks (16 females, 7 males, 9 unknown), ranging from 2.4 to 5.2 m total length, with satellitebased tags to investigate broad-scale movements in the North Atlantic. Based on 10427 days of tracking data. We found that white sharks are more broadly distributed, both horizontally and vertically, throughout the North Atlantic than previously understood, exhibiting an ontogenetic shift from near-coastal, shelf-oriented habitat to pelagic habitat with frequent excursions to mesopelagic depths. During the coastal phase, white sharks migrated seasonally from the northeast shelf in the summer to overwintering habitat off the southeastern US and the Gulf of Mexico, spending 95% of their time at <50 m depth. During the pelagic phase, subadult and adult white sharks exhibited wide-ranging movements during the fall, winter, and spring into the broader Atlantic over a 30° latitudinal range and as far east as the Azores. These sharks moved daily to depths of up to 1128 m, spending significant time at specific mesopelagic depth zones through a temperature range of 1.6 to 30.4°C. We believe these movements are associated with offshore foraging facilitated by the thermal physiology of the species. Our findings extend the known essential habitat for the white shark in the North Atlantic beyond existing protection, with implications for future conservation.
... As an apex predator, white sharks exert top-down pressure throughout pelagic and coastal shelf regions and exhibit ontogenetic changes in diet and distribution as they mature from juveniles to adults (Estrada et al., 2006;Hussey et al., 2012;Kim et al., 2012;Grainger et al., 2020;Machovsky-Capuska and Raubenheimer, 2020). In the WNA, biotelemetry studies have shown the majority of white sharks to engage in large scale seasonal migrations along the US east coast, traveling from Atlantic Canada and New England waters in the summer to the Carolinas, Florida, the Bahamas, and the Gulf of Mexico during winter months (Curtis et al., 2014;Skomal et al., 2017;Guttridge et al., 2024). Juvenile WNA white sharks consume predominantly bony fish, squid, and elasmobranchs before transitioning to include more lipid-dense animals such as marine mammals in adulthood (Estrada et al., 2006;Casey and Pratt, 1985), which is hypothesized to support greater migratory capacity and the increased energetic demands of their endothermic metabolism, as well as reproduction and active foraging in colder waters (Klimley, 1985;Watanabe et al., 2015;Grainger et al., 2020;Machovsky-Capuska et al., 2016;Skomal et al., 2017;Franks et al., 2021). ...
... In the WNA, biotelemetry studies have shown the majority of white sharks to engage in large scale seasonal migrations along the US east coast, traveling from Atlantic Canada and New England waters in the summer to the Carolinas, Florida, the Bahamas, and the Gulf of Mexico during winter months (Curtis et al., 2014;Skomal et al., 2017;Guttridge et al., 2024). Juvenile WNA white sharks consume predominantly bony fish, squid, and elasmobranchs before transitioning to include more lipid-dense animals such as marine mammals in adulthood (Estrada et al., 2006;Casey and Pratt, 1985), which is hypothesized to support greater migratory capacity and the increased energetic demands of their endothermic metabolism, as well as reproduction and active foraging in colder waters (Klimley, 1985;Watanabe et al., 2015;Grainger et al., 2020;Machovsky-Capuska et al., 2016;Skomal et al., 2017;Franks et al., 2021). In particular, gray seal (Halichorerus grypus) colonies are thought to provide a valuable source of energy to foraging subadult and adult white sharks along the northeast continental shelf of the North American continent (Skomal et al., 2012, Skomal et al., 2017Grainger et al., 2020;Moxley et al., 2020;Franks et al., 2021;Winton et al., 2021). ...
... Juvenile WNA white sharks consume predominantly bony fish, squid, and elasmobranchs before transitioning to include more lipid-dense animals such as marine mammals in adulthood (Estrada et al., 2006;Casey and Pratt, 1985), which is hypothesized to support greater migratory capacity and the increased energetic demands of their endothermic metabolism, as well as reproduction and active foraging in colder waters (Klimley, 1985;Watanabe et al., 2015;Grainger et al., 2020;Machovsky-Capuska et al., 2016;Skomal et al., 2017;Franks et al., 2021). In particular, gray seal (Halichorerus grypus) colonies are thought to provide a valuable source of energy to foraging subadult and adult white sharks along the northeast continental shelf of the North American continent (Skomal et al., 2012, Skomal et al., 2017Grainger et al., 2020;Moxley et al., 2020;Franks et al., 2021;Winton et al., 2021). While significant progress has been made towards understanding the movement patterns and habitat use of juvenile and adult white sharks in the WNA, particularly near aggregation sites at Cape Cod, Massachusetts (Winton et al., 2021), and Nova Scotia, Canada (Bowlby et al., 2022), substantial knowledge gaps regarding white shark distribution and habitat use within parts of their range remain (Curtis et al., 2014). ...
While significant progress has been made to characterize life history patterns, movement ecology, and regional estimates of abundance of white sharks (Carcharodon carcharias) in the Western North Atlantic (WNA), patterns of spatial distribution remain relatively unknown in the northern Gulf of Maine. In this study, we utilize data collected from multiple acoustic telemetry projects from 2012-2023 to assess the spatiotemporal distribution of white sharks along sections of the Maine coastline and regional offshore waters. Acoustic receivers were deployed each year from 2012-2019 (mean number of receivers ± SD: 11 ± 4), and effort increased following the first-ever white shark related fatality in Maine in 2020 (2020-2023: 40 ± 15). In total, 107 white sharks tagged by researchers in the WNA were detected, with the majority (n = 90) detected in shallow (<50 m depth) waters post-2019. Reflective of the tagged population at-large, total length of individuals ranged from 2.1 to 4.9 m, with most individuals estimated to be in the juvenile or subadult life stages. White sharks were detected between the months of May-December, with peaks between July and September, and were observed in close proximity to several of Maine’s western beaches and islands/outcroppings, with higher numbers observed at several sites in eastern Casco Bay. Although the overall quantity of detections was relatively low when compared to white shark aggregation sites in other regions, this study provides baseline information on the presence of this species in the northern Gulf of Maine. While future research should include expanded receiver coverage in eastern Maine and the use of additional tagging technologies, this study contributes early insights for informing marine spatial planning, fisheries management, and conservation strategies for white sharks in the region.
... In the instance of white sharks (Carcharodon carcharias), there are nine known C. carcharias subpopulations: Southern-Western Australia (Bruce, 2016;McAuley et al., 2017), Western North Atlantic (WNA, Skomal et al., 2017), Northeastern Pacific (NEP, Domeier and Nasby-Lucas, 2013), Eastern Australian and New Zealand (Bruce et al., 2019), Mediterranean (Leone et al., 2020), South African (Kock et al., 2013), Northwest Pacific (Tanaka et al., 2011), South American Atlantic (Cione and Barla, 2008), and South American Pacific (Bustamante et al., 2014; Figure 1). Due to its low rebound potential and current estimated population status, C. carcharias is listed as vulnerable on a global scale (Rigby et al., 2019) according to the International Union for the Conservation of Nature Red List. ...
... While extensive tagging efforts have provided a baseline understanding of the movements of most C. carcharias populations (e.g. Skomal et al., 2017;Bruce et al., 2019), there remains uncertainty as to the structure, size, and range of most subpopulations, particularly in the Northwest Pacific population (Christiansen et al., 2014). ...
... Southern-Western Australian and Eastern Australian and New Zealand) or from the Northwest Pacific subpopulation, it is further uncertain as to why, how frequently, and for what duration they are utilizing these tropical waters. It is not uncommon for C. carcharias to utilize tropical waters as they have a global distribution in temperate, subtropical, and tropical seas (Bonfil et al., 2005(Bonfil et al., , 2010Duffy et al., 2012;Skomal et al., 2017). However, research illustrates that C. carcharias movement patterns have been suggested to be correlated with a variety of both biotic and abiotic variables, including reproductive behaviour (e.g. ...
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In 2013 and 2019, two separate encounters with a white shark (Carcharodon carcharias) were documented within Indonesian waters. Of particular importance was ca. 6.0 m male C. carcharias that was captured in Lombok, Indonesia in 2013, where an upper lateral tooth was retained. Using the D-loop sequences of the mitochondrial DNA (mtDNA) associated with this captured white shark, the mtDNA was compared to the available mtDNA sequences in GenBank® associated with the Northwest Pacific and Australian (i.e. Southern-Western and Eastern) C. carcharias subpopulations to determine its point of origin. Results from the mtDNA analyses suggest that the point of origin for this captured C. carcharias is from one of the Australian subpopulations. When compared to primary literature, this migration presents a northerly range extension for this species; however, since it is unclear what Australian subpopulation this shark was from it is uncertain what subpopulation this range extension applies to. Although C. carcharias presence within Indonesian waters is likely a rare occurrence, being that Indonesia represents the largest shark fin exporter in the world, the utilization of these waters and potential unsustainable exploitation poses a definitive threat to this highly migratory top predator. Therefore, further research investigating the purpose and site fidelity of C. carcharias within these waters is critical to future multijurisdictional protection of this top predator.
... Large marine mammals, such as odontocete whales (e.g., Orcas Orcinus orca) maintain much higher internal temperatures (close to 40°C; Whittow et al., 1974;Strøm et al., 2019) and so were not considered as a potential predator in this instance. Two endothermic predator candidates large enough to predate upon mature porbeagles and located within the vicinity and at the time of year of the predation event include the white shark Carcharodon carcharias (Skomal et al., 2017) and shortfin mako Isurus oxyrhinchus (Santos et al., 2021). Following ontogenetic shifts in diet, prey species of adult white sharks and shortfin makos are known to include other elasmobranch species (and marine mammals) (e.g., Joyce et al., 2002). ...
... Following ontogenetic shifts in diet, prey species of adult white sharks and shortfin makos are known to include other elasmobranch species (and marine mammals) (e.g., Joyce et al., 2002). While fine-scale diving data for these potential predators are limited in the location that the predation event occurred, both white sharks (Skomal et al., 2017) and shortfin makos (Santos et al., 2021;FIGURE 1 Map of the capture location, the single highest-accuracy daily finmount tag transmission, and the first transmission received from the PSAT after pop-off for a pregnant porbeagle tagged in the Northwest Atlantic. It is important to note that there is a time gap between the last depth measurement collected from the PSAT and the first transmission after pop-off. ...
... However, tagged shortfin makos mainly occupied depths less than 400 m and made rapid oscillatory dives between the sea surface and deeper depths during the day while in offshore waters of the North Atlantic (Santos et al., 2021;Loefer et al., 2005), which was not characteristic of the predator's behavior in this study. In comparison to shortfin makos, large female white sharks spent more time at depths of 400-600 m while in mesopelagic waters of the North Atlantic (Skomal et al., 2017). Given this comparison, a white shark was likely the predator of our tagged porbeagle. ...
Pop-off satellite archival tags (PSATs) have been increasingly deployed on marine megafauna to remotely monitor their movements, behavior, and environmental preferences. These tags have also allowed the occasional novel documentation of ecological interactions, such as predation on tagged animals. A PSAT deployed on a pregnant porbeagle Lamna nasus in the Northwest Atlantic suggests the shark was predated upon in mesopelagic waters near Bermuda. Predation was evident approximately 5 months after tagging based on depth and temperature data transmitted by the PSAT. Four days prior to PSAT pop-off, depth data indicated that the tag continued to descend and ascend in the water column while the temperature remained approximately 5°C above ambient levels, even at several hundred meters in depth, indicating ingestion. Given the location of predation and elevated temperature at depth recorded by the pregnant porbeagle’s tag, potential predators include endothermic shark species such as the white shark Carcharodon carcharias and shortfin mako Isurus oxyrhinchus. This is the first evidence of predation on a porbeagle globally and provides novel insight into inter-specific interactions for this large, threatened shark species.
... Large juvenile, subadult, and adult white sharks seasonally aggregate near pinniped colonies often when water temperatures correspond to their preferred range (Klimley et al., 2001;Bruce and Bradford, 2015;Hewitt et al., 2018;Kock et al., 2022;Winton et al., 2023). Much of our understanding of white shark movement ecology comes from studies where animals are tracked with acoustic or satellite tags at these sites (e.g., Neptune Islands, South Australia; Guadalupe Island, Mexico; California and Cape Cod, U.S.A), which have documented philopatric behaviors, such as high site fidelity, seasonal residency as well as long-distance return migrations (Bonfil et al., 2005;Jorgensen et al., 2010;Bruce and Bradford, 2015;Skomal et al., 2017;Huveneers et al., 2018;Bastien et al., 2020). ...
... Despite these measures and evidence of recovery, only recently have we begun to learn about their horizontal and vertical space use in the NWA, through various biotelemetry studies (Skomal et al., 2017;Bastien et al., 2020;Lowerre-Barbieri et al., 2021;Franks et al., 2021;Winton et al., 2021;Bowlby et al., 2022). Adult white sharks have been shown to exhibit an ontogenetic shift in their space use from near-coastal, shelf-oriented waters to pelagic habitat, with frequent excursions to mesopelagic depths (Skomal et al., 2017). ...
... Despite these measures and evidence of recovery, only recently have we begun to learn about their horizontal and vertical space use in the NWA, through various biotelemetry studies (Skomal et al., 2017;Bastien et al., 2020;Lowerre-Barbieri et al., 2021;Franks et al., 2021;Winton et al., 2021;Bowlby et al., 2022). Adult white sharks have been shown to exhibit an ontogenetic shift in their space use from near-coastal, shelf-oriented waters to pelagic habitat, with frequent excursions to mesopelagic depths (Skomal et al., 2017). White sharks migrate to the southeast shelf waters of North Carolina to Florida during the late fall when water temperatures generally drop below 12°C in the NWA (Casey and Pratt, 1985;Curtis et al., 2014;Skomal et al., 2017;Bowlby et al., 2022), with some individuals traveling as far as the Gulf of Mexico in winter and early spring (Skomal et al., 2017;Franks et al., 2021). ...
The white shark, Carcharodon carcharias, is an iconic apex predator, playing an important ecological role across its range. Persistent bycatch and overfishing led to white shark declines, but recent studies in the North Western Atlantic (NWA) revealed evidence for regional recovery, and highlighted the importance of Southeastern Florida and the Gulf of Mexico as overwintering grounds for maturing white sharks. However, despite its proximity to Florida and comparably productive habitats, records of white sharks in The Bahamas are extremely rare, with a comprehensive survey of sightings and captures describing only one white shark between 1800 - 2010. Here, we reveal acoustic tracking detections of ten white sharks from 2020 - 2024 along the western edge of the Tongue of the Ocean off Central Andros Island, The Bahamas. White sharks were originally tagged off the coast of the United States and Canada, and detected off Andros Island, The Bahamas from November-May. White sharks were detected along the drop-off zone of the reef at ca. 25 m, exclusively between dusk and dawn, with the number of detections suggesting transient behavior. These findings expand our knowledge of white shark distribution in the NWA, highlighting data gaps in The Bahamas and underlining the importance of collaborative protective measures for species recovery.
... This study will characterize landscapes of white shark relative abundance and identify hot spot areas to be monitored and further investigated, as it already happens in other oceanic sectors of the white shark distribution (Bruce & Bradford, 2012;Francis et al., 2012;Huveneers, Watanabe, et al., 2018b;Jorgensen et al., 2010;Kock et al., 2022;Skomal et al., 2017). This information is crucial to building effective conservation plans and preventing species' local extinction. ...
... Unfortunately, the number of white shark sightings was insufficient for complete space-time modeling. White sharks exhibit complex seasonal migrations in other ocean sectors, highly varying by sex, age, and region (Bradford et al., 2020;Francis et al., 2012;Kock et al., 2022;Skomal et al., 2017). We do not know whether Mediterranean white sharks show similar spatio-temporal patterns. ...
... The Mediterranean Sea is warmer than other oceanic regions where white sharks occur (Rohling et al., 2015). While, its average annual sea surface temperature (SST) is within the white shark optimal temperature range (10-23 • C) (Boustany et al., 2002;Bruce & Bradford, 2012;Domeier & Nasby-Lucas, 2008;Francis et al., 2012;Skomal et al., 2017;Weng et al., 2007), Mediterranean SST can reach 29-30 • C peaks during the summer in the central (Di Lorenzo et al., 2018) and eastern sectors (Rohling et al., 2015). Although we cannot completely exclude the emerging pattern is associated with an underestimation of the observation effort, considering the paucity of both historical and more recent occurrences from the eastern Mediterranean sectors, the warmer and less productive waters of that basin (Bosc et al., 2004;Coll et al., 2010) may be a sub-optimal habitat for the species . ...
Conserving oceanic apex predators, such as sharks, is of utmost importance. However, scant abundance and distribution data often challenge understanding the population status of many threatened species. Occurrence records are often scarce and opportunistic, and fieldwork aimed to retrieve additional data is expensive and prone to failure. Integrating various data sources becomes crucial to developing species distribution models for informed sampling and conservation purposes. The white shark, for example, is a rare but persistent inhabitant of the Mediterranean Sea. Here, it is considered Critically Endangered by the IUCN, while population abundance, distribution patterns, and habitat use are still poorly known. This study uses available occurrence records from 1985 to 2021 from diverse sources to construct a spatial log-Gaussian Cox process, with data-source specific detection functions and thinning, and accounting for physical barriers. This model estimates white shark presence intensity alongside uncertainty through a Bayesian approach with Integrated Nested Laplace Approximation (INLA) and the inlabru R package. For the first time, we projected species occurrence hot spots and landscapes of relative abundance (continuous measure of animal density in space) throughout the Mediterranean Sea. This approach can be used with other rare species for which presence-only data from different sources are available.
... This highly migratory species has low fecundity, producing 2-14 pups per litter (Francis 1996;Saïdi et al. 2005;Uchida et al. 1996), slow growth (Natanson and Skomal 2015;Wintner and Cliff 1999), and late sexual maturity (Natanson and Skomal 2015), which is estimated to occur at > 3.80 m total length (TL) for males and > 4.50 m TL for females (Francis 1996;Pratt 1996;Wintner and Cliff 1999). There are seven well-studied white shark populations: Southern-Western Australia (Bruce 2016;McAuley et al. 2017), Western North Atlantic (WNA, Franks et al. 2021;Skomal et al. 2017), Northeastern Pacific (NEP, Domeier and Nasby-Lucas 2013), Eastern Australian and New Zealand (Bruce et al. 2019), Mediterranean (Agostino Leone et al. 2020), South Africa (Kock et al. 2013), and Northwest Pacific (Tanaka et al. 2011;Fig. 1). ...
... In the Western North Atlantic (WNA), catch data in combination with extensive tagging research have provided a comprehensive understanding of C. carcharias migratory patterns Franks et al. 2021;Skomal et al. 2017). Sharks exhibit a large migratory range, extending from Newfoundland, Canada to the Gulf of Mexico, USA (Franks et al. 2021;Skomal et al. 2017; Fig. 1). ...
... In the Western North Atlantic (WNA), catch data in combination with extensive tagging research have provided a comprehensive understanding of C. carcharias migratory patterns Franks et al. 2021;Skomal et al. 2017). Sharks exhibit a large migratory range, extending from Newfoundland, Canada to the Gulf of Mexico, USA (Franks et al. 2021;Skomal et al. 2017; Fig. 1). Presently, one large and expansive nursery area has been identified in this region: the New York Bight (Casey and Pratt 1985;Curtis et al. 2018;O'Connell et al. 2021). ...
The white shark (Carcharodon carcharias) is a globally distributed top predator. Due to its ecological importance and historical declining population trends, data contributing to conservation initiatives (e.g. habitat protections and resource management) pertaining to all life stages of this species are essential to facilitate population recovery. Of particular interest, the locations and discrete seasonality of C. carcharias parturition remain uncertain. Understanding C. carcharias parturition in relation to each population is relevant to population recovery since neonate to young-of-the-year (YOY) sharks are more vulnerable to predation and particularly threatened by and susceptible to commercial fishing pressure. Herein, this paper provides a synthesis from published literature across seven well-studied C. carcharias populations to identify common trends associated with parturition location, seasonality, and habitat characteristics. The data reviewed in this study are consistent with previous population-specific hypotheses, that C. carcharias parturition occurs during spring and summer for all populations. Further, this review also indicates that parturition likely occurs in insular shelf waters and water temperatures ranging from15.7 to 23.1 °C. Although discrete parturition sites were not identified, the compiled data are suggestive that C. carcharias parturition may occur over horizontal and vertical spatial scales that exceed the inshore, shallow water environments associated with nursery area habitat to perhaps minimize predation by conspecifics. Due to the vulnerability of C. carcharias, conducting non-lethal technological (e.g., baited remote underwater video systems—BRUVS), morphological (i.e., ontogenetic changes in dorsal fin shape), and reproductive (e.g., blood chemistry and ultrasonography) research that may help identify parturition location and seasonality are thus warranted.
... These are problematic constraints for species that are highly migratory, such as the white shark. Individual white sharks travel thousands of kilometers each year to optimize foraging opportunities but are only available to survey efforts at coastal aggregation sites that constitute a small fraction of their overall range (Domeier & Nasby-Lucas 2013, Skomal et al. 2017. Although many white sharks exhibit long-term fidelity to aggregation sites ), short-term patterns of space use and residency at such sites vary widely among individuals, and not all individuals visit aggregation sites every year (Domeier & Nasby-Lucas 2013, Skomal et al. 2017. ...
... Individual white sharks travel thousands of kilometers each year to optimize foraging opportunities but are only available to survey efforts at coastal aggregation sites that constitute a small fraction of their overall range (Domeier & Nasby-Lucas 2013, Skomal et al. 2017. Although many white sharks exhibit long-term fidelity to aggregation sites ), short-term patterns of space use and residency at such sites vary widely among individuals, and not all individuals visit aggregation sites every year (Domeier & Nasby-Lucas 2013, Skomal et al. 2017. Therefore, individual sharks have variable degrees of exposure to sampling as a function of their location relative to survey efforts; if ignored, this heterogeneity in encounter probabilities can result in biased population estimates that would be misleading if used as the basis for management advice (Burgess et al. 2014). ...
... A pilot study conducted during the summer and fall of 2014 proved this approach feasible (see Section 3); there fore, the survey was expanded and conducted seasonally from 2015− 2018. Available tagging data indicated clear seasonal movement patterns and a high degree of variation in residency and habitat use (Skomal et al. 2017, Winton et al. 2021). Therefore, survey trips were conducted twice a week when conditions allowed from late June through October to capture the aggregation's seasonal dynamics and increase the chance that 'transient' individuals would be encountered. ...
The present study provides the first estimate of abundance for the white shark at a new aggregation site in the western North Atlantic, which required the development of a novel modeling framework to accommodate the species’ migratory behavior. Estimates of abundance are needed to evaluate the performance of existing conservation measures for white shark populations worldwide but have historically been infeasible to obtain in the region. Following the recent emergence of Cape Cod, Massachusetts, USA, as a seasonal aggregation site, we conducted a photographic capture-recapture survey and identified 393 individual white sharks from 2015-2018. As conventional capture-recapture models do not adequately represent the species’ migratory behavior, we extended an existing open spatial capture-recapture framework to allow for movements into and out of the surveyed area and accommodate variation in residency and habitat use among individuals. Using simulations, we demonstrated that failing to account for these processes resulted in biased estimates of abundance that would be misleading if used as the basis for management advice. We applied the model developed to describe the seasonal dynamics of the Cape Cod aggregation site and estimated a superpopulation size of 800 (393-1286) individuals, which provides an important baseline for this species of conservation concern. Because it directly links changes in abundance over time to the demographic processes underpinning them, the model described provides a more mechanistic understanding of the dynamics of white shark aggregations and improves the applied relevance of the results for the conservation and management of the species.
... In juvenile and adult white sharks, Carcharodon carcharias (Linnaeus 1758), shelforiented movements and occasional oceanic migrations are well-documented globally [4][5][6]. Similarly, vertical movements of the species have been relatively well studied in the Pacific and Indian Ocean e.g., [5,7,8], and to a lesser extent in the Atlantic [9][10][11][12]. Reported dive and horizontal patterns show a wide range of inter-individual, geographic and temporal variation in both ocean-and shelf-phases and are temporally inconsistent, complicating the development and verification of hypotheses about their ecological role. ...
... In contrast, archival data of adult white sharks in the Pacific revealed clear spatial patterning of diel vertical migration (DVM) behaviour [28,29]. Although most authors have attributed observed diving patterns to prey searching and navigation e.g., [10,26], drivers of vertical movement patterns in white sharks remain speculative across their circumglobal range. ...
... During continental-shelf phases, sharks spent most of their time between the surface and depths of 20-50 m. This corroborates previous research, suggesting that these depths are preferred by all life stages of the species across its range [4,6,7,10,11,21,[24][25][26][43][44][45][46]. Habitat choice is largely the result of matching abiotic preferences, e.g., temperature, with ecological factors, such as prey availability, predation risk and competition. ...
Knowledge of the 3-dimensional space use of large marine predators is central to our understanding of ecosystem dynamics and for the development of management recommendations. Horizontal movements of white sharks, Carcharodon carcharias, in eastern Australian and New Zealand waters have been relatively well studied, yet vertical habitat use is less well understood. We dual-tagged 27 immature white sharks with Pop-Up Satellite Archival Transmitting (PSAT) and acoustic tags in New South Wales coastal shelf waters. In addition, 19 of these individuals were also fitted with Smart Position or Temperature Transmitting (SPOT) tags. PSATs of 12 sharks provided useable data; four tags were recovered, providing highly detailed archival data recorded at 3-s intervals. Horizontal movements ranged from southern Queensland to southern Tasmania and New Zealand. Sharks made extensive use of the water column (0–632 m) and experienced a broad range of temperatures (7.8–28.9 °C). Archival records revealed pronounced diel-patterns in distinct fine-scale oscillatory behaviour, with sharks occupying relatively constant depths during the day and exhibiting pronounced yo-yo diving behaviour (vertical zig-zag swimming through the water column) during the night. Our findings provide valuable new insights into the 3-dimensional space use of Eastern Australasian (EA) white sharks and contribute to the growing body on the general ecology of immature white sharks.
... White sharks (Carcharodon carcharias, Linnaeus 1758) are a large, circumglobally distributed, apex predator that play an important regulatory role in many marine habitats from the continental shelf to pelagic seas, and in surface waters down to depths of 1280 m [1][2][3][4][5]. In Australia, white sharks are broadly distributed in southern waters, primarily ranging from North West Cape, Western Australia to central Queensland [6][7][8]. ...
... Corroborating previous research of subadult and adult white sharks, tracked individuals in this study also spent most of the time in offshore and pelagic waters [4,7,37,39]. W1 recorded the greatest longitudinal point of 155° E, with W2 and W3 recording a maximum of 154° E. ...
... Seasonal movement has also been described in white shark populations in the north Atlantic [4], and northeast Pacific [39]. Individuals >300 cm were reported displaying a less defined pattern of seasonal movement in offshore and pelagic habitats [4]. ...
In eastern Australia, white sharks (Carcharodon carcharias) are targeted in shark control programs, yet the movement of subadults and adults of the eastern Australasian population is poorly understood. To investigate horizontal and vertical movement and habitat use in this region, MiniPAT pop-up satellite archival tags were deployed on three larger white sharks (340–388 cm total length) between May 2021 and January 2022. All sharks moved away from the coast after re- lease and displayed a preference for offshore habitats. The upper < 50 m of the water column and temperatures between 14–19 °C were favoured, with a diel pattern of vertical habitat use evident as deeper depths were occupied during the day and shallower depths at night. Horizontal movement consisted of north–south seasonality interspersed with periods of residency. Very little information is available for adult white sharks in eastern Australia and studies like this provide key baseline information for their life history. Importantly, the latitudinal range achieved by white sharks illu- minate the necessity for multijurisdictional management to effectively mitigate human-shark inter- actions whilst supporting conservation efforts of the species.
... In the western North Atlantic, juvenile white sharks (<3 m TL) are primarily coastal and migrate seasonally. They spend winter along the southeast U.S. coast and spring/summer between Cape Hatteras and Cape Cod (Curtis et al., 2014;Skomal et al., 2017). Sub-adult and adult distributions are similar to those of juveniles during summer months, but are more variable during fall, winter, and spring, with some traveling beyond the continental shelf (Skomal et al., 2017). ...
... They spend winter along the southeast U.S. coast and spring/summer between Cape Hatteras and Cape Cod (Curtis et al., 2014;Skomal et al., 2017). Sub-adult and adult distributions are similar to those of juveniles during summer months, but are more variable during fall, winter, and spring, with some traveling beyond the continental shelf (Skomal et al., 2017). ...
... Detections of white sharks at Gray's Reef indicate this sanctuary is a seasonal coastal habitat for multiple life stages and both sexes of this species. Timing of these detections match their known seasonal distribution in the western Atlantic, occurring along the southeast U.S. coast during winter and spring (Curtis et al., 2014;Skomal et al., 2017). Although almost half of tagged subadult/adult white sharks move beyond the continental shelf in the winter and spring (Skomal et al., 2017), 17 sub-adults/adults visited Gray's Reef, a coastal habitat, during those seasons (Figure 3.33). ...
This study analyzed nearly ten years of acoustic telemetry monitoring at Gray’s Reef National Marine Sanctuary, to understand its role in fish movements along the U.S. Atlantic coast. Designated in 1981, Gray’s Reef lies 19 miles off the coast of Georgia where water depths are ~60-70 feet and the habitat is comprised of a mosaic of ledges, flat live-bottom, and unconsolidated sediments. Biotic communities there are seasonally influenced by warm waters from the south and cooler temperate waters from the north. The unique geographic location and complex habitat provided by Gray’s Reef attracts many transient fish species, however a quantitative understanding of the timing and frequency of their presence is lacking. Here, we identify all transient species that were detected by telemetry receivers at the sanctuary from 2008 to 2017, summarize the timing and seasonality of their visits, and discuss their connectivity to the broader coastal Atlantic ecosystem.
... Contemporary research using multiple tag technologies to obtain longer-term datasets has yielded key insights into how aquatic animals interact with their environment (e.g., Vaudo et al., 2017;Braun et al., 2019;Cochran et al., 2019;Hoffmayer et al., 2021), potential drivers of vertical and horizontal movement (e.g., Coffey et al., 2017;Gaube et al., 2018;Lee et al., 2021), and how space use changes through ontogeny (e.g., Skomal et al., 2017;Ajemian et al., 2020), while also providing critical information for the implementation of effective management and conservation strategies (e.g., Acuña-Marrero et al., 2017;White et al., 2017;Bangley et al., 2020). In recent years, studies using pop-up satellite-linked archival tags (PSATs) on sharks have revealed long-term movement and migration routes as well as habitat use patterns (e.g., Weng et al., 2007a,b;Pade et al., 2009;Comfort and Weng, 2015). ...
... Studies from various regions around the world show that most white sharks exhibit migratory and residency behaviors (Bruce et al., 2006;Duffy et al., 2012;Skomal et al., 2017;Lee et al., 2021) and in many instances these movement phases are predictable (Weng et al., 2007a;Jorgensen et al., 2010;Duffy et al., 2012). Drivers of these movements have been suggested to be abiotic factors including temperature or currents as well as biotic factors such as mating, pupping, prey availability, or predation risk Domeier and Nasby-Lucas, 2013;Hoyos-Padilla et al., 2016;Skomal et al., 2017;Jorgensen et al., 2019). ...
... Studies from various regions around the world show that most white sharks exhibit migratory and residency behaviors (Bruce et al., 2006;Duffy et al., 2012;Skomal et al., 2017;Lee et al., 2021) and in many instances these movement phases are predictable (Weng et al., 2007a;Jorgensen et al., 2010;Duffy et al., 2012). Drivers of these movements have been suggested to be abiotic factors including temperature or currents as well as biotic factors such as mating, pupping, prey availability, or predation risk Domeier and Nasby-Lucas, 2013;Hoyos-Padilla et al., 2016;Skomal et al., 2017;Jorgensen et al., 2019). White sharks from multiple ocean basins have been shown to spend considerable time in coastal over-shelf waters with regular offshore, pelagic phases (Bonfil et al., 2005;Jorgensen et al., 2010;Domeier, 2012;Duffy et al., 2012;Bradford et al., 2020). ...
Understanding how mobile, marine predators use three-dimensional space over time is central to inform management and conservation actions. Combining tracking technologies can yield powerful datasets over multiple spatio-temporal scales to provide critical information for these purposes. For the white shark (Carcharodon carcharias), detailed movement and migration information over ontogeny, including inter- and intra-annual variation in timing of movement phases, is largely unknown in the western North Atlantic (WNA), a relatively understudied area for this species. To address this need, we tracked 48 large juvenile to adult white sharks between 2012 and 2020, using a combination of satellite-linked and acoustic telemetry. Overall, WNA white sharks showed repeatable and predictable patterns in horizontal movements, although there was variation in these movements related to sex and size. While most sharks undertook an annual migratory cycle with the majority of time spent over the continental shelf, some individuals, particularly adult females, made extensive forays into the open ocean as far east as beyond the Mid-Atlantic Ridge. Moreover, increased off-shelf use occurred with body size even though migration and residency phases were conserved. Summer residency areas included coastal Massachusetts and portions of Atlantic Canada, with individuals showing fidelity to specific regions over multiple years. An autumn/winter migration occurred with sharks moving rapidly south to overwintering residency areas in the southeastern United States Atlantic and Gulf of Mexico, where they remained until the following spring/summer. While broad residency and migration periods were consistent, migratory timing varied among years and among individuals within years. White sharks monitored with pop-up satellite-linked archival tags made extensive use of the water column (0–872 m) and experienced a broad range of temperatures (−0.9 – 30.5°C), with evidence for differential vertical use based on migration and residency phases. Overall, results show dynamic inter- and intra-annual three-dimensional patterns of movements conserved within discrete phases. These results demonstrate the value of using multiple tag types to track long-term movements of large mobile species. Our findings expand knowledge of the movements and migration of the WNA white shark population and comprise critically important information to inform sound management strategies for the species.
... This knowledge gap is a potential barrier to conservation as understanding a species spatial ecology, including habitat preferences and migratory behaviours, are essential to implement effective management and conversation strategies . Historically, mapping demersal elasmobranch occurrence has been largely based on bottom-trawl data (Martin et al. 2012;Skomal et al. 2017;ICES 2023). Because tows are often quite widely spaced these surveys provide broad spatial patterns, but fish abundances are averaged along the tow length which can complicate interpretation of preferred habitats in heterogeneous environments. ...
... Recent advances in technology have seen increasing application of telemetry to elasmobranch studies, for example, biologging tags such as pop-up satellite-linked archival tags (PSATs) (Skomal et al. 2017), acoustic transmitters and 'smart' position or temperature transmitting (SPOT) tags (Franks et al. 2021). Such methods have greatly increased our understanding of the movements of individual sharks (e.g., Hammerschlag, Gallagher, and Lazarre 2011;Schaber et al. 2022;Renshaw et al. 2023; Thorburn et al. 2023), skates (e.g., Kneebone et al. 2020;Lavender et al. 2022) and rays (e.g., Brewster et al. 2021). ...
To implement effective management and conservation strategies, an understanding of the spatial ecology, habitat preferences and movement of demersal elasmobranchs is required. This study combines a photographic survey obtained from an autonomous underwater vehicle (AUV) with existing bathymetric data to help understand elasmobranch ecology within the Firth of Lorn, western Scotland. This area is within the Loch Sunart to Sound of Jura Marine Protected Area (MPA) and designated for the protection of the critically endangered flapper skate (Dipturus intermedius). Two areas of seabed were surveyed using an AUV in water depths of 110-165 m southwest of the Isle of Kerrera. Eight surveys were conducted in total, four in each area. Each area was surveyed twice over 2 days in October 2020 and twice in 2 days in May June 2021. One day used bait on the seabed (October) whilst all the others had no bait. For each survey, the AUV travelled 17 km at a height of 2 m above the seabed in a lawnmower pattern providing 0.5 km 2 photographic coverage for ~2 h per survey. Five elasmobranch species, two scyliorhinids (Scyliohinus canicula and Galeus melastomus) and three rajiformes (D. intermedius, Raja clavata and Leucoraja naevus), were identified from a total of 43 k seabed photographs. In total 42 individual animals and 7 egg cases were observed. Although the AUV had short survey times and small study areas the results are encouraging for AUVs being a useful tool in understanding elasmobranch ecology.
... The white shark Carcharodon carcharias is a prime example of a large-bodied shark that exhibits ontogenetic shifts in its distribution and which faces conservation threats (Rigby et al. 2022). Specifically, juvenile white sharks use coastal habitats more frequently than adults (Kerr et al. 2006, Carlisle et al. 2012, Skomal et al. 2017. These coastal areas are considered to be white shark 'nurseries' if they meet all of these criteria: exhibit a high density of young-of-year (YOY) individuals relative to other areas, relatively high site fidelity of those YOY individuals, and persistence of use across years (Heupel et al. 2007). ...
... Future research using UAVs could perform targeted behavioral observations, rather than density surveys as performed in this study, to better understand such drivers and the variable influence of these factors on different shark size classes. Part of the challenge of explaining shark density using these modeling ap proaches derives almost certainly from the fact that white sharks exhibit complex interannual patterns with inshore-offshore dynamics that vary ontogenically (Kerr et al. 2006, Carlisle et al. 2012, Jorgensen et al. 2012, Skomal et al. 2017. A more extended time series of UAV observations might better document these types of patterns and lead to more holistic explanations of variation in local shark density. ...
Ontogenetic habitat shifts are a common feature of many marine species, including sharks, which face conservation threats when their distributions overlap with human resource extraction and habitat modification. White sharks Carcharodon carcharias , for example, exhibit a distinctly coastal phase as juveniles, with a limited distribution compared to the basin-scale range of adults. Using an unoccupied aerial vehicle (UAV), we studied a coastal aggregation site within a Southern California Bight nursery area to determine how fine-scale temporal and oceanographic factors affect white sharks at different developmental stages. White shark density, as measured via UAV, was highly variable across time of day and day of year, with modest variation across years. Typically, more sharks were observed in the late afternoon hours. Sharks, especially those <3 m total length, were observed more often during periods of colder seafloor temperatures, potentially reflecting avoidance of these colder, deeper waters by more cold-intolerant smaller white sharks. Alternate models incorporating sea surface temperature showed a very small but significant association between surface temperatures and <3 m total length white sharks for the months we surveyed, but no such association for larger sharks. There were no or only modest effects of visibility, swell height, chl a levels, sea state, and tidal height on UAV-observed shark density. Understanding how temporal patterns and oceanographic predictors of density change over time as well as how shark ontogeny interacts with these factors can help us to better understand how this species uses coastal habitats and predict when they may be more likely to share marine space with humans.
... Francis (1996) summarized the available information on white sharks from multiple populations and concluded that most females mature within the size range 450-500 cm TL. A more recent report on WNA white sharks (Skomal et al. 2017) used similar length ranges for life stages, but these ranges were obtained from a study of the eastern Australia population (Bruce & Bradford 2012) due to a lack of information for the WNA population. More recently, Franks et al. (2021) provided information on size by life stage in the WNA by classifying male and fe male white sharks into juvenile, subadult, maturing (for females only), and mature life stages. ...
... Its usefulness can range from comparing the L 50 -to-maximum length ratio to knowing the fraction of the mature population for age-structured models. In species of conservation interest whose capture is difficult or impossible, life history analyses from observations of free-swimming animals are problematic (Castro 2012, Skomal et al. 2017. Such uncertainty in estimating the size of free-swimming individuals inevitably affects the judgments of life stages, potentially impacting management decisions based on population parameters. ...
Length at life stages of the white shark Carcharodon carcharias is not well known for most of the 9 populations of this species, including in the western North Atlantic (WNA). We analyzed length and maturity data by sex for 87 white sharks with sizes ranging 138-501 cm total length (TL), captured, studied, and released by OCEARCH during 2012-2022, off the US and Canadian Atlantic coasts. A binary logistic regression was used to estimate the length-at-maturity ( L 50 ) for the WNA white shark with a Bayesian statistical framework using a Markov chain Monte Carlo method for numerical integration. Different trials using noninformative and informative priors were tested. The posterior probability distribution for L 50 , steepness of the model (φ), and 95% credible intervals (CI) of the logistic model for females were L 50 = 411.3 cm TL (CI: 390.8-432.6 cm TL) and φ = 10.5 (CI: 5.7-17.8) and for males were L 50 = 334.9 cm TL (CI: 321.2-348.2 cm TL) and φ = 7.5 (CI: 4.2-12.4). These L 50 values are somewhat smaller than previously reported sizes-at-maturity for both sexes of this species. An ordinal logistic regression allowed us to determine the probability of being in the various life stages (young-of-the-year, juvenile, and adult) at a particular size. Estimating the length at any life-history stage of white sharks along with age estimates is useful for determining the reproductive value of the population and ultimately for estimating the relative contribution (elasticity) of vital rates to population growth.
... These included 219 sharks tagged on the Canaveral Shoals including blacknose (n = 57), finetooth (55), scalloped hammerhead (39), sharpnose (38), and lemon sharks (30), plus 348 sharks from twelve species tagged by researchers over a wide area from south Florida and the Bahamas to Nova Scotia, Canada (Table 3). Blacktip shark was the most commonly detected species (n = 114), and all species recorded in the Canaveral Array were also collected on longlines with the exception of white sharks (48) and common thresher shark (1). Acoustic telemetry better documented the presence of larger species relative to longline catches. ...
... Changes in the shark assemblage across seasons were pronounced and somewhat anticipated. Long distance migrations, while only now being resolved in detail for many coastal sharks thanks to improved tagging technology (see [46][47][48][49][50]), have been broadly recognized for decades in the US Atlantic and many other regions of the world. Although not presented in detail here, a majority of blacknose, finetooth, sharpnose, and lemon sharks acoustically tagged at Cape Canaveral undertook northward spring migrations before returning to east Florida in fall [27,41], and over 200 sharks tagged by other researchers from South Florida and Bahamas to Canada migrated through the project area. ...
Offshore sand shoals are a coveted sand source for coastal restoration projects and as sites for wind energy development. Shoals often support unique fish assemblages but their habitat value to sharks is largely unknown due to the high mobility of most species in the open ocean. This study pairs multi-year longline and acoustic telemetry surveys to reveal depth-related and seasonal patterns in a shark community associated with the largest sand shoal complex in east Florida, USA. Monthly longline sampling from 2012–2017 yielded 2,595 sharks from 16 species with Atlantic sharpnose (Rhizoprionodon terraenovae), blacknose (Carcharhinus acronotus), and blacktip (C. limbatus) sharks being the most abundant species. A contemporaneous acoustic telemetry array detected 567 sharks from 16 species (14 in common with longlines) tagged locally and by researchers elsewhere along the US East Coast and Bahamas. PERMANOVA modeling of both datasets indicate that the shark species assemblage differed more across seasons than water depth although both factors were important. Moreover, the shark assemblage detected at an active sand dredge site was similar to that at nearby undisturbed sites. Water temperature, water clarity, and distance from shore were habitat factors that most strongly correlated to community composition. Both sampling approaches documented similar single-species and community trends but longlines underestimated the shark nursery value of the region while telemetry-based community assessments are inherently biased by the number of species under active study. Overall, this study confirms that sharks can be an important component of sand shoal fish communities but suggests that deeper water immediately adjacent to shoals (as opposed to shallow shoal ridges) is more valuable to some species. Potential impacts to these nearby habitats should be considered when planning for sand extraction and offshore wind infrastructure.
... Nowadays, the cetacean apex predator is the killer whale (Orcinus orca; Delphinidae, Odontoceti), which thanks to its large size and coordinated hunting strategies can feed upon sperm whales as well as large baleen whales (mysticetes) like common minke whales (Balaenoptera acutorostrata), calves of humpback whales (Megaptera novaeangliae), and grey whales (Eschrichtius robustus) (Pitman et al. 2001(Pitman et al. , 2015Barrett-Lennard et al. 2011;Ford 2018). In modern oceans, the killer whale shares the top position of the trophic chains with the great white shark (Carcharodon carcharias), whose predatory activity on diminutive marine mammals is widely known (Compagno 1984;Heithaus 2001;Brown et al. 2010;Skomal et al. 2017;Moro et al. 2020). ...
... According to our estimates, Zygophyseter varolai was able to generate the same bite force as a great white shark individual well beyond sexual maturity (Kohler et al. 1996;Wroe et al. 2008). Extant Carcharodon carcharias is known as a highly generalist predator that mainly feeds upon diminutive and fat-rich marine mammals, such as fur seals and small toothed whales (Compagno 1984;Heithaus 2001;Brown et al. 2010;Skomal et al. 2017;Moro et al. 2020). Several field studies and laboratory analyses have demonstrated that extant white sharks prey upon marine mammals Berta and Lanzetti (2020), with the addition of the grip-and-shear feeding (illustration of Zygophyseter varolai modified from Bianucci and Landini 2006). in adulthood, when they reach a body length of 300-400 cm (Long and Jones 1996;Estrada et al. 2006). ...
Differing from the extant physeteroids, macroraptorial sperm whales are currently regarded as apex predators of the Miocene seas based on several morphofunctional observations. Here, we estimate the bite force of Zygophyseter varolai, a macroraptorial physeteroid from lower upper Miocene strata of the Pietra leccese formation (Apulia, Italy) using the finite element analysis (FEA). To explore multiple bite scenarios, we set four different load cases on a 3D model of the cranium obtained via digital photogram-metry, considering the temporalis and masseter muscles as jaw adductors. Our FEA simulations indicate that Z. varolai exerted an anterior bite force of more than 4000 N and a posterior bite force of more than 10000 N. These values are similar to those estimated for other marine predators known for their powerful bite. This suggests that Z. varolai might have fed upon medium-sized marine vertebrates like other odontocetes. Considering the significant difference observed between the anterior and posterior bite forces, Z. varolai likely fed via 'grip-and-shear' feeding, snapping the food items with an anterior bite and then cutting them with a powerful posterior bite. Other macroraptorial sperm whales such as the roughly coeval Acrophyseter from Peru likely employed the same feeding technique. ARTICLE HISTORY
... PTT 200368/222133 that migrated to the GOM), with a decrease in residency behavior when they moved offshore. Direct movements are often associated with dispersal and are consistent with previous tracks of great hammerheads and other large migratory sharks (Lea et al., 2015;Skomal et al., 2017;Guttridge et al., 2022). ...
In light of global declines of upper-level marine predators, such as the great hammerhead, ( Sphyrna mokarran) a thorough understanding of their behavioral ecology is needed for designing effective management strategies to preserve their key role in maintaining ecosystem functioning, stability, and resilience. Within the northwestern Atlantic, great hammerheads display regional connectivity between the U.S. East Coast and the western edge of The Bahamas, but despite the suggested importance of the Bahamian shark sanctuary towards regional population recovery strategies, relatively few data exist from other areas of The Bahamas. This study used fisheries-independent drumline captures, satellite telemetry, and bulk stable isotope analysis to advance our understanding of the residency, space use, and trophic role of great hammerheads in Andros, the largest island in The Bahamas. We examined movement behaviors and thermal range within the Bahamian Exclusive Economic Zone, and constructed Bayesian mixing models based on carbon, nitrogen, and sulfur isotope ratios to estimate the importance of prey species in the diet of great hammerheads. Our data revealed year-round residency of Andros-caught great hammerheads in Bahamian waters with site-fidelity to and high use of habitats along the reef-drop off and flats of Andros. Great hammerheads predominantly fed on barracuda and small-bodied elasmobranchs in Andros connecting food webs from the pelagic zone to the shoreline. This study expands our knowledge of the ecology of great hammerheads in the northwestern Atlantic and shows that, despite their highly-mobile nature, some individuals reside in the Bahamas year round. These findings suggest the Bahamian shark sanctuary could be more than just a seasonal refuge for this species as previously proposed, and merit further research to assess the conservation value of the sanctuary towards regional rebuilding goals for greathammerheads.
... However, if †O. megalodon was capable of at least cruising as fast as the slowest lamnid, Carcharodon carcharias (Sayama et al., 2024; see above), it is possible that †O. megalodon could have exhibited a migrating behavior like the extant C. carcharias (e.g., Skomal et al., 2017, and references therein), which has an average cruising speed (3.5 km h -1 ; see above) comparable to Rhincodon and Cetorhinus. ...
... Estos resúmenes, en forma de histogramas de tiempo en temperatura (time-at-temperature, TAT por sus siglas en inglés), pueden ser usados como proxy del comportamiento de buceo cuando existe información del gradiente de la temperatura en la columna de agua (Joyce et al., 2016), como es el caso del Golfo de México (e. g., Rivas et al., 2005, Sheinbaum et al., 2007. Los histogramas TAT han sido ampliamente utilizados para analizar la distribución en los estratos térmicos de la columna de agua en varias especies de vertebrados marinos, como tiburones (e. g., Tyminski et al., 2015;Skomal et al., 2017) y tortugas (e. g., Dodge et al., 2014;Wildermann et al., 2019). En contraste, su uso en cetáceos ha sido muy limitado, aunque fue validado como un buen descriptor del comportamiento de buceo en cinco especies de odontocetos, incluyendo al calderón tropical (Joyce et al., 2016). ...
El comportamiento de buceo de los calderones (Globicephala spp.) ha sido estudiado en diferentes regiones del océano Atlántico, sin embargo, en esta tesis se presentan los primeros hallazgos sobre el comportamiento de buceo del calderón tropical (G. macrorhynchus) en el Golfo de México. En abril de 2018 se colocaron marcas satelitales LIMPET-SPOT (Wildlife Computers, WA) en siete calderones (dos machos adultos, MA, y cinco hembras adultas/machos subadultos, HA/MS) en aguas del sur de Veracruz. Estas marcas, además de la posición, transmiten registros periódicos de la proporción de tiempo que los animales pasan en diferentes intervalos de temperatura de la columna de agua, resumidos en histogramas de frecuencia de tiempo en temperatura (TAT). Se registraron un total de 180 histogramas TAT en un período de transmisión de 87 d. Los intervalos de temperatura se transformaron a estratos de profundidad con el método Gravest Empirical Mode utilizando datos de tres boyas perfiladoras ARGO. Se identificaron dos estados conductuales: inmersiones someras de no forrajeo (< 50 m) e inmersiones de forrajeo ( 50 m), que a su vez se dividieron en inmersiones poco profundas [50 - 290 m) y profundas ( 290 m). Se utilizó un enfoque bayesiano para evaluar posibles diferencias en la proporción de tiempo usado en estos estados tomando en cuenta tres horarios (matutino, vespertino y nocturno), y los clases de sexo (MA y HA/MS). En general, los calderones pasaron 60% del tiempo en inmersiones de no forrajeo (intervalo de credibilidad del 95%, 95%ICr: 55 – 61%), y 30% (95%ICr: 28 – 33%) en inmersiones poco profundas durante el forrajeo. La proporción de tiempo que pasaron en los estratos de profundidad presentó una distribución unimodal durante la noche y bimodal en el día (horarios matutino y vespertino), coincidente con la migración vertical diurna de sus presas principales (calamares). Los MA permanecieron más tiempo en inmersiones profundas (19%, 95%ICr: 17 – 22%) que los HA/MS (9%, 95%ICr: 7 – 11%), sugiriendo segregación del hábitat de forrajeo relacionado con el tamaño de los individuos.
... Positions were derived for coastal shark species, several of which typically associate with offshore pelagic environments (the white shark and common thresher shark, [23,45]). While positioning errors were comparable to other species , the total number of derived positions was comparatively low (435 unique positions across seven species), suggesting that effective monitoring of highly migratory sharks will require increased tagging efforts (including transmitters with faster transmission rates) and array expansion. ...
Rapid global expansion of offshore wind farms, tidal, and wave technologies signifies a new era of renewable energy development. While a promising means to combat the impacts of climate change, such developments necessitate fine-scale monitoring of biological communities to determine impacts associated with construction, operation, and eventual decommission. Here, we evaluate the performance of a gridded, Innovasea Systems, Inc. fine-scale acoustic telemetry positioning system (FSPS, n = 20 acoustic receivers) for tracking behaviors of diverse, temperate fish assemblages in relation to a subsea cable route supporting the Ørsted offshore wind development in coastal New York. We examined array performance through positioning error derived from receiver reference transmitters and tracked animals (n = 260) comprising 17 species of teleost and elasmobranch. We evaluated the effects of environmental variables (temperature, tilt, noise, and depth), transmitter power, individual movement rates, and receiver loss on horizontal positioning error (HPE) and route mean squared error (RMSE). Across a 16-month deployment period, many positions were derived for Atlantic sturgeon (n = 2,612), black sea bass (n = 9,175), clearnose skate (n = 10,306), summer flounder (n = 13,304), and little skate (n = 15,186), suggesting that these species may serve as sentinel candidates for assessing behavioral changes following construction, operation, and decommission. We found that receivers placed at the boundary of the grid exhibited higher HPE and RMSE, however these errors did not significantly change despite large receiver losses (25%). Generalized Linear Models revealed that temperature, noise, tilt, and depth were often significant predictors of HPE and RMSE, however, a substantial amount of variance was not explained by the models (~ 70%). Average movement rates ranged from 1.1 m s⁻¹ (common thresher shark) to 0.03 m s⁻¹ (little skate and summer flounder) but had minimal effects on positioning error. Finally, we observed that higher transmitter powers (158 dB) may lead to higher and more variable HPE values. Overall, these findings provide new insight into the drivers of FSPS array performance and illustrate their broad utility for monitoring fish behavior associated with offshore marine developments.
... Telemetry studies reveal that immature white sharks undertake seasonal north-south migrations, spending increased time in southern Queensland and northern New South Wales from September, before moving to southern New South Wales and Victorian waters in March (Spaet et al., 2020b). Similar patterns of seasonal movement have been reported in the North Atlantic (Skomal et al., 2017;Franks et al., 2021), South Africa (Towner et al., 2013), and the north-east Pacific (Weng et al., 2007). Although highly migratory, immature white sharks spend more time in so-called 'nursery' areas between Lake Macquarie (33.3°S) and South West Rocks (30.8°S), returning in consecutive years (Bruce et al., 2019). ...
White sharks (Carcharodon carcharias) play a crucial ecological role, shaping ecosystems through direct predation and risk effects. On the east coast of Australia, immature white sharks are broadly distributed, inhabiting a wide range of habitats and ecosystems from temperate Tasmania to tropical North Queensland. Using stable isotopes and fatty acids of muscle and plasma, we examined the diet and habitat use of 136 immature white sharks (152–388 cm total length) captured on SMART drumlines on the East Australian coast. This facilitated the temporal assessment of white shark trophic ecology from a few weeks to approximately a year. Biochemistry of muscle samples showed that white sharks predominantly feed on low trophic level prey from coastal environments. A seasonal shift in diet was evident, with the increasing proportions of essential fatty acids in muscle tissues during spring and summer suggesting a greater consumption of high-nutrition preys during those months compared to autumn and winter. By combining stable isotope and fatty acid analysis, we gain a comprehensive understanding of immature white shark diet in eastern Australia. Our results confirm that white sharks are generalist predators that exhibit seasonal shifts in their diet. Their high use of coastal habitats reinforces the importance of these areas for foraging, which is crucial for growth and development during this critical life stage.
... White sharks Carcharodon carcharias provide an interesting model species to test the influence of internal and external factors on predator movement ecology. They are endothermic top predators and tagging studies indicate they range across a vast area of subtropical and temperate oceanic environments globally but aggregate with high fidelity around distinct foraging areas often near pinniped colonies (Bruce & Bradford, 2015;Chapple et al., 2011;Huveneers et al., 2018;Klimley & Ainley, 1996;Skomal et al., 2017;Winton et al., 2023). Several factors influence coastal residency periods, movements, and behaviors of white sharks during these aggregations, particularly the presence of a predictable high-calorie prey source at pinniped colonies (Huveneers et al., 2018;Jorgensen et al., 2012;Klimley, Le Boeuf, Cantara, Richert, Davis, Van Sommeran, & Kelly, 2001;Kock et al., 2022;Towner et al., 2013). ...
An animal's movement is influenced by a plethora of internal and external factors, leading to individual‐ and habitat‐specific movement characteristics. This plasticity is thought to allow individuals to exploit diverse environments efficiently. We tested whether the movement characteristics of white sharks Carcharodon carcharias differ across ontogeny and among habitats along the coast of Central California. In doing so, we elucidate how changes in internal state (physiological changes coinciding with body size) and external environments (differing seascapes and/or diel phases) shape the movement of this globally distributed predator. Twenty‐one white sharks, from small juveniles to large adults, were equipped with motion‐sensitive biologging tags at four contrasting seascapes: two islands, a headland, and an inshore cove. From multisensor biologging data, 20 metrics characterizing movement (i.e., depth use, vertical velocities, activity, turning rates, and bursting events) were derived and subjected to multivariate analyses. Movement characteristics were most different across seascapes, followed by ontogeny and diel phase. Juvenile sharks, which were only encountered at the cove, displayed the most distinct movement characteristics. Sharks at this seascape remained close to the shore traveling over smaller areas, shallower depth ranges, and with lower levels of tail beat frequencies, when corrected for size, than sub‐adult and adult sharks tagged elsewhere. Distinct tortuous daytime versus linear nighttime horizontal movements were recorded from sharks at island seascapes but not from those at the headland or inshore cove. At the offshore islands, the linear nighttime swimming patterns coincided with repeated dives to and from deeper water. The availability of prey and access to deeper water are likely drivers of the differences in movement characteristics described, with varying demographics of pinniped prey found at the subadult and adult aggregation areas and juvenile sharks being piscivorous and their habitat neither adjacent to pinniped haul out areas nor deeper water. This study demonstrates plasticity in the movements of a top predator, which adapts its routine to suit the habitat it forages within.
... The great white shark (WS), Carcharodon carcharias (Linnaeus, 1758) (Lamniformes: Lamnidae), is widely distributed in tropical and temperate regions of all oceans with temperatures ranging from the 5°C of Alaska to 27°C observed in tropical areas, such as Durban (Martin, 2003;Compagno et al., 2005). Recently, it was observed that the WS can reach a depth of 1128 m with temperature variations between 1.6 and 30°C (Skomal et al., 2017). The use of satellite telemetry on WSs off South Africa and the West Coast of the United States (Bonfil et al., 2005;Weng et al., 2007) showed that they can cross ocean basins and use pelagic habitats for months. ...
Described in the present report are documented attempts to tag and sample the white shark, Carcharodon carcharias (Linnaeus, 1758), along Italian coasts in the Mediterranean Sea, which took place near the Lampedusa Island in the lower Tyrrhenian Channel of Sicily, off the coast of Rimini in the Adriatic Sea, and of Civitavecchia in the central Tyrrhenian Sea. The project, activated in 2015, was aimed at tagging and sampling specimens of the white shark in order to collect data useful to implement conservation strategies in the Mediterranean Sea. Despite four tagging attempts made in 2017, 2018, 2021, and 2022 with 288 total hours of baiting activity and the use of 1030 kg of chum, no white sharks or any other shark species were sighted.
Sažetak: POKUŠAJI LOCIRANJA I UZORKOVANJA VELIKE BIJELE PSINE, CARCHARODON CARCHARIAS (LAMNIFORMES: LAMNIDAE), UZ TALIJANSKU OBALU U SREDOZEMNOM MORU. U radu su dokumentirani pokušaji označavanja i uzorkovanja velike bijele psine Carcharodon carcharias (Linnaeus, 1758) uz talijansku obalu u Sredozemnom moru. Istraživanje je obavljeno na području oko otoka Lampeduze, u sicilijanskom kanalu u južnom Tirenskom moru, ispred Riminija u Jadranskom moru te kod Civitavecchije u centralnom Tirenskom moru. Projekt, koji je započeo 2015. godine, bio je usmjeren na označavanje i uzorkovanje primjeraka velike bijele psine s ciljem prikupljanja podataka važnih za implementaciju mjera za očuvanje populacije ove vrste u Sredozemnom moru. Unatoč četiri pokušaja označavanja obavljena 2017., 2018., 2021. i 2022. godine, u ukupnom trajanju od 288 sati primamljivanja uz pomoć mamca te 1030 kg mamca, ni jedan primjerak velike bijele psine, ni drugih vrsta morskih pasa, nije primijećen.
... The great white shark (WS), Carcharodon carcharias (Linnaeus, 1758) (Lamniformes: Lamnidae), is widely distributed in tropical and temperate regions of all oceans with temperatures ranging from the 5°C of Alaska to 27°C observed in tropical areas, such as Durban (Martin, 2003;Compagno et al., 2005). Recently, it was observed that the WS can reach a depth of 1128 m with temperature variations between 1.6 and 30°C (Skomal et al., 2017). The use of satellite telemetry on WSs off South Africa and the West Coast of the United States (Bonfil et al., 2005;Weng et al., 2007) showed that they can cross ocean basins and use pelagic habitats for months. ...
Described in the present report are documented attempts to tag and sample the white shark, Carcharodon carcharias (Linnaeus, 1758), along Italian coasts in the Mediterranean Sea, which took place near the Lampedusa Island in the lower Tyrrhenian Channel of Sicily, off the coast of Rimini in the Adriatic Sea, and of Civitavecchia in the central Tyrrhenian Sea. The project, activated in 2015, was aimed at tagging and sampling specimens of the white shark in order to collect data useful to implement conservation strategies in the Mediterranean Sea. Despite four tagging attempts made in 2017, 2018, 2021, and 2022 with 288 total hours of baiting activity and the use of 1030 kg of chum, no white sharks or any other shark species were sighted.
... Previous research has shown that White Sharks undergo regular long-distance movements [56,[74][75][76][77]. Further, individuals exhibit site fidelity at various stages of their travels, particularly juvenile sharks, which regularly visit important nearshore areas. ...
Simple Summary: Conflicts between humans and sharks have often been dealt with by catching and killing sharks. However, there is now a growing demand for methods that protect water users from shark bites while minimizing harm to all species. Shark-Management-Alert-in-Real-Time (SMART) drumlines, a new non-lethal shark mitigation method, alert responders when an animal takes the bait, giving them the opportunity to quickly respond. In a study conducted in New South Wales, Australia, 36 White Sharks (Carcharodon carcharias) were caught using SMART drumlines and tagged with satellite-linked radio transmitters (SLRTs) and acoustic tags before being released to examine the short-term post-release movements and longer-term fate of White Sharks after capture, tagging, and release. During the first three days after release, the sharks moved away from the shore and stayed mostly offshore. Although sharks gradually moved closer to the shore 10 days after release, 77% of the sharks remained more than 1.9 km away from the coast and an average of 5 km away from where they were tagged. The sharks were acoustically detected for an average of 591 days after release, with detections ranging from 45 to 1075 days, highlighting longer-term survival. Although five out of the 36 sharks were not detected by the acoustic receivers, the SLRTs indicated that these sharks were alive and well, with detections ranging from 43 to 639 days after release. These findings demonstrate the effectiveness of SMART drumlines as a non-lethal method to mitigate bites by White Sharks.
Abstract: Human-shark conflict has been managed through catch-and-kill policies in most parts of the world. More recently, there has been a greater demand for shark bite mitigation measures to improve protection for water users whilst minimizing harm to non-target and target species, particularly White Sharks (Carcharodon carcharias), given their status as a Threatened, Endangered, or Protected (TEP) species. A new non-lethal shark bite mitigation method, known as the Shark-Management-Alert-in-Real-Time (SMART) drumline, alerts responders when an animal takes the bait and thereby provides an opportunity for rapid response to the catch and potentially to relocate, tag, and release sharks. Thirty-six White Sharks were caught on SMART drumlines in New South Wales, Australia, and tagged with dorsal fin-mounted satellite-linked radio transmitters (SLRTs) and acoustic tags before release. Thirty-one sharks were located within 10 days, 22 of which provided high-quality locations (classes 1 to 3) suitable for analysis. Twenty-seven percent and 59% of these sharks were first detected within 10 and 50 h of release, respectively. For the first three days post-release, sharks moved and mostly remained offshore (>3.5 km from the coast), irrespective of shark sex and length. Thereafter, tagged sharks progressively moved inshore; however, 77% remained more than 1.9 km off the coast and an average of 5 km away from the tagging location, 10 days post-release. Sharks were acoustically detected for an average of 591 days post-release (ranging from 45 to 1075 days). Although five of the 36 sharks were not detected on acoustic receivers, SLRT detections for these five sharks ranged between 43 and 639 days post-release, indicating zero mortality associated with capture. These results highlight the suitability of SMART drumlines as a potential non-lethal shark bite mitigation tool for TEP species such as White Sharks, as they initially move away from the capture site, and thereby this bather protection tool diminishes the immediate risk of shark interactions at that site.
... m and females around 4.5-4.8 m (Bruce and Bradford, 2012;Curtis et al., 2014;Skomal et al., 2017;Weng et al., 2007) at approximately ages of 26 and 36 years respectively (Natanson and Skomal, 2015). White sharks are apex predators (trophic level 4.5+) (Estrada et al., 2006) whose feeding habits include pinnipeds, cetaceans, and fishes such as elasmobranchs, ground fishes, and tunas (Arnold, 1972;Carey et al., 1982;Casey and Pratt Jr, 1985;Curtis et al., 2014;Turnbull and Dion, 2012). ...
... Individual white sharks are highly mobile and regularly exhibit transient movements interspersed with periods of residency at specific aggregation sites and/or localized regions (Skomal et al. 2017;Duffy et al. 2012;Jorgensen et al. 2010;Franks et al. 2021;Kock et al. 2022). Prey availability is a key driver for movement and occurrence of predators, including white sharks Hoyos-Padilla et al. 2016;Kock et al. 2013). ...
... These reveal the geographic and vertical movements of individuals and the association between them. Typically, studies categorize three most common vertical movements: foraging, predator avoidance and bio-energetic swimming behaviour (e.g. by following specific water currents) (Skomal et al., 2017;Strøm et al., 2018;Wilson and Block, 2009). However, directed migrations also require orientation and navigation abilities that are likely represented in vertical movements, but still poorly understood. ...
... White sharks Carcharodon carcharias provide an interesting model species to test the influence of internal and external factors on predator movement ecology. They are endothermic top predators and tagging studies indicate they range across a vast area of subtropical and temperate oceanic environments globally but aggregate with high fidelity around distinct foraging areas often near pinniped colonies (Bruce & Bradford, 2015;Chapple et al., 2011;Huveneers et al., 2018;Klimley & Ainley, 1996;Skomal et al., 2017;Winton et al., 2023). Several factors influence coastal residency periods, movements, and behaviors of white sharks during these aggregations, particularly the presence of a predictable high-calorie prey source at pinniped colonies (Huveneers et al., 2018;Jorgensen et al., 2012;Klimley, Le Boeuf, Cantara, Richert, Davis, Van Sommeran, & Kelly, 2001;Kock et al., 2022;Towner et al., 2013). ...
An animal’s movement is influenced by a plethora of internal and external factors, leading to individual- and habitat-specific movement characteristics. This plasticity is thought to allow individuals to exploit diverse environments efficiently. We tested if the movement characteristics of white sharks Carcharodon carcharias differ across ontogeny and among habitats along the coast of Central California. In doing so, we elucidate how changes in internal state (physiological changes coinciding with body size) and external environments (differing seascapes and/or diel phases) shape the movement of this globally distributed predator. White sharks, from small juveniles to large adults, were equipped with motion-sensitive biologging tags at four contrasting seascapes: two islands, a headland, and an inshore cove. From multi-sensor biologging data, 20 metrics characterising movement were derived and subjected to multivariate analyses. Movement characteristics were most different across seascapes, followed by ontogeny and diel phase. Juvenile sharks, that were only encountered at the cove, displayed the most distinct movement characteristics. Sharks at this seascape remained close to the shore and were comparatively less active than sub-adult and adult sharks tagged elsewhere. Distinct night-time movements and dive patterns were recorded from sharks at an island seascape but not from those at the headland or inshore cove. The availability of prey and access to deeper water are likely drivers, with greater numbers of Northern elephant seals Mirounga angustirostris at the island seascapes and harbour seals Phoca vitulina at the headland seascape, while the offshore island group is also closer to the continental shelf edge. Juvenile sharks at the inshore cove are piscivorous and their habitat was not adjacent to pinniped haul out areas nor deeper water. This study demonstrates plasticity in the movements of a top predator, that adapts its routine to suit the habitat it forages within.
... Movimientos horizontales, migraciones y segregación sexual Las migraciones son un fenómeno enormemente extendido en el reino animal, en muchos casos motivados por factores ecológicos y biogeográficos como son fines tróficos, reproductivos o sociales (Alerstam et al., 2003;Bowler and Benton, 2005;Milner-Gulland et al., 2011;. Estos pueden darse a diferentes escalas, cubriendo incluso importantes desplazamientos o movimientos transoceánicos en algunas especies de escualos como es el caso del tiburón blanco Bruce et al., 2006;Weng et al., 2007;Camhi and Pikitch, 2008;Hoyos-Padilla et al., 2016;Skomal et al., 2017;Spaet et al., 2020), el tiburón peregrino (Gore et al., 2008;Braun et al., 2018;Dewar et al., 2018), la tintorera (Camhi and Pikitch, 2008;Queiroz et al., 2010Queiroz et al., , 2012Queiroz et al., , 2017Campana et al., 2011;Vandeperre et al., 2014a;Kohler and Turner, 2019;Vedor et al., 2021a) o el tiburón ballena (Wilson et al., 2006;Brunnschweiler et al., 2009;Schmidt et al., 2009;Hueter et al., 2013;Diamant et al., 2018), con impresionantes desplazamientos. Otras especies de predadores marinos, como los atunes (Block et al., 1998Brill et al., 1999;Walli et al., 2009), tortugas marinas , cetáceos Nowacek et al., 2016;Reisinger et al., 2018), pinnípedos Carter et al., 2016;Reisinger et al., 2018) y aves marinas Horton et al., 2014;Weimerskirch et al., 2016;Reisinger et al., 2018) presentan también migraciones de larga distancia. ...
In the present work, key aspects of the biology and ecology of the shortfin mako were studied. Feeding habits, analysed in two ocean basins, indicated that pelagic fish and cephalopods were the main prey items. In the South Pacific Ocean, a marked sexual segregation was found, with females being more common in the SE region; this was also the area with a higher abundance of juveniles and of late-stage pregnant females. In the North Atlantic Ocean, large-scale horizontal movements (including trans-Atlantic migrations) were identified and diel vertical behaviour patterns described. Importantly, individuals that performed wider movements away from the tagging location were less at risk from surface longline fishing. Using tagging and recapture data that spanned a ten-year period, survival, dispersal, and fishing mortality rates for both mako and blue sharks were estimated. The presence of plastics and hooks was also observed for both species, in two studied ocean basins. Finally, bycatch rates for other internationally protected shark species that are commonly caught using surface longlines was estimated based on direct observations, which were several times higher than the official reported data. The results presented here are especially relevant for improving the management measures focused on pelagic sharks.
... Indeed, they could efficiently regulate their body temperature, allowing them to dwell in cold waters (Pimiento et al., 2016). In addition, they may have frequented deep waters like their modern analogue, the great white shark (Pimiento et al., 2016), which can dive as deep as 1000 m (Skomal et al., 2017). Therefore, their habitat may have had different salinity ranges than modern sharks, and additional biological factors could have influenced their Li isotopic signatures. ...
The vertebrate fossil record documents a plethora of transitions between aquatic and terrestrial environments but their causes are still debated. Quantifying the salinity of living environments is therefore crucial for precising the sequence of ecological transitions. Here, we measured lithium stable isotope composition of mineralized tissues (δ7Limt) of extant and extinct vertebrates from various aquatic environments: seawater, freshwater/terrestrial, and “transitional environments” (i.e. brackish waters, or seasonal access to freshwater and seawater). We report statistically higher δ7Limt values for seawater vertebrates than freshwater ones, taxonomic groups considered separately. Moreover, vertebrates living in transitional environments have intermediate δ7Limt values. Therefore, we show that δ7Limt values of both extant and extinct vertebrates can discriminate their aquatic habitat.
... White sharks are known to opportunistically target turtles while seeking more desirable prey, such as other elasmobranchs and teleosts, but more in-depth information on these interactions is limited because turtles typically constitute only a small portion of white sharks' diet (Fergusson et al. 2000). White shark movement is frequently monitored in the Paci c and Indian Oceans due to their seasonal aggregations near pinniped colonies that facilitate observational studies (Skomal et al. 2017). In northern California in the 1990s, two stranded leatherback turtles had wounds attributed to predation by white sharks, with both turtles missing large portions of their carapace and hind limbs; however, it was unclear whether the sharks were directly responsible for the turtles' deaths or if the wounds occurred postmortem (Long 1996). ...
Sharks are the primary predator of large immature and mature sea turtles, yet the shark species responsible for both lethal and non-lethal injuries are rarely identified because attacks are infrequently observed. Forensic analysis of bite wounds can be used to accurately assess size and potential shark species, especially when combined with species-specific feeding behavior, geographic distribution, and habitat preference. The objective of this study was to use forensic analysis of bite damage on sea turtles to infer shark size and species. Photographs from thirteen cases of documented shark scavenging ( N = 3) and predation ( N = 10) attempts on sea turtles were retrospectively analyzed, including nesting, free-ranging, and/or dead stranded loggerhead ( Caretta caretta ), green ( Chelonia mydas ), Kemp’s ridley ( Lepidochelys kempii ), and leatherback ( Dermochelys coriacea ) sea turtles in Florida and Alabama, USA from 2010–2020. Mean interdental distance (IDD) and bite circumference (BC) of wound marks on sea turtles strongly suggest that the bite marks were generated by white sharks ( Carcharodon carcharias ) in three cases, tiger sharks ( Galeocerdo cuvier ) in three cases, and bull shark(s) ( Carcharhinus leucas ) in one case. For three cases with less distinct wound patterns, two likely shark species were identified, and thereafter narrowed down to a single species based on bite mark characteristics. Due to indistinct IDD and BC ranges of bite wound patterns, a single shark species was not identified in three cases. Forensic analysis enables more accurate evaluations of which shark species predate and scavenge sea turtles, and is a useful technique for studying the behavioral interactions of sharks and turtles more closely.
... Observing the behaviour of highly mobile marine predators is challenging as they spend most or all of their time at sea, often far from land or underwater, and can cover large distances (Fedak et al., 2002;Luschi et al., 2003;Skomal et al., 2017). Animalborne sensors allow for the collection of fine-scale data from which the movements of marine predators can be reconstructed (Wilmers et al., 2015). ...
Understanding how marine predators find patchily distributed prey resources in a dynamic environment is key to identifying important ecological areas for ecosystem-level conservation management. However, the mechanisms underpinning important foraging areas often result from complex interactions between static and dynamic covariates (e.g. topography and currents). Modelling habitat associations with hydrodynamic processes is rarely useful when attempting to identify and characterise foraging areas across an individual’s foraging range. Investigating the influence of static habitat features on predator behaviour can provide a more tractable baseline understanding of habitat associations, upon which additional complexity can be added. Seabed gradient covariates (e.g. slope and aspect) are often used, yet such metrics are computed at singular user-defined resolutions, and provide limited ecological insight when used in isolation. Instead, categorising the seabed into geomorphological features may provide better characterisation of seabed structure. Here we explore the utility of a pattern recognition algorithm to delineate whole geomorphological features (“geomorphons”) on the seabed (e.g. valleys, ridges, footslopes) from bathymetry data, and examine the influence of geomorphology on marine predator habitat use. We demonstrate the potential application of this approach in a case study, examining the influence of geomorphons on the at-sea behaviour of a highly mobile predator inhabiting shelf seas: the grey seal (Halichoerus grypus). We analyse GPS tracking data from three seals tagged in the southern North Sea, an area with heterogeneous geomorphology. We use hidden Markov models (HMMs) to infer foraging and travelling behaviour and model the effect of different feature types on the probability of switching between states. All three seals showed an increased probability of transitioning from travelling to foraging when encountering slopes, footslopes and hollows, and foraging activity was concentrated at slopes on the fringes of the Dogger Bank. We hypothesise that such features may host prey aggregations, and/or lead to increased prey capture success. The results suggest the importance of such areas for grey seals in the southern North Sea, a region undergoing rapid and widespread anthropogenic habitat change. This method could be incorporated into future species distribution models to improve estimates of predator distribution, informing conservation management and marine spatial planning.
... Mature sharks may also need to travel wider and further to find suitable mates. The seasonal occurrence of white sharks is pronounced at all major aggregation sites worldwide (Klimley et al., 2001;Martin et al., 2005;Anderson et al., 2011;Dicken and Booth, 2013;Kock et al., 2013;Bruce and Bradford, 2015;Skomal et al., 2017). In our study, the season also influenced the behavioural state of white sharks, with juvenile females and subadult males more likely to be in a resident state during the austral winter months. ...
Human activities in the oceans increase the extinction risk of marine megafauna. Interventions require an understanding of movement patterns and the spatiotemporal overlap with threats. We analysed the movement patterns of 33 white sharks (Carcharodon carcharias) satellite-tagged in South Africa between 2012 and 2014 to investigate the influence of size, sex and season on movement patterns and the spatial and temporal overlap with longline and gillnet fisheries and marine protected areas (MPAs). We used a hidden Markov model to identify ‘resident’ and ‘transient’ movement states and investigate the effect of covariates on the transition probabilities between states. A model with sex, total length and season had the most support. Tagged sharks were more likely to be in a resident state near the coast and a transient state away from the coast, while the probability of finding a shark in the transient state increased with size. White sharks moved across vast areas of the southwest Indian Ocean, emphasising the need for a regional management plan. White sharks overlapped with longline and gillnet fisheries within 25% of South Africa’s Exclusive Economic Zone and spent 15% of their time exposed to these fisheries during the study period. The demersal shark longline fishery had the highest relative spatial and temporal overlap, followed by the pelagic longline fishery and the KwaZulu-Natal (KZN) shark nets and drumlines. However, the KZN shark nets and drumlines reported the highest white shark catches, emphasising the need to combine shark movement and fishing effort with reliable catch records to assess risks to shark populations accurately. White shark exposure to shark nets and drumlines, by movement state, sex and maturity status, corresponded with the catch composition of the fishery, providing support for a meaningful exposure risk estimate. White sharks spent significantly more time in MPAs than expected by chance, likely due to increased prey abundance or less disturbance, suggesting that MPAs can benefit large, mobile marine megafauna. Conservation of white sharks in Southern Africa can be improved by implementing non-lethal solutions to beach safety, increasing the observer coverage in fisheries, and continued monitoring of movement patterns and existing and emerging threats.
... Individuals from multiple reef-associated shark species reliably arrive at and prey upon fish spawning aggregations elsewhere in tropical marine environments (Mourier et al., 2016;Olsen & LaPlace, 1979;Pickard et al., 2016;Rhodes et al., 2019). Further, the repeated return of highly migratory sharks to prey aggregations has been documented globally (Guttridge et al., 2017;Hacohen-Domené et al., 2015;Jorgensen et al., 2010;Schilds et al., 2019;Skomal et al., 2017), suggesting a potential link between memory and successful foraging events. Within the study site and across consecutive years, individual great hammerheads, identified by external tags or unique fin morphologies, have been observed feeding on tarpon or recaptured at known tarpon prespawning aggregation sites (G. A. Casselberry, unpublished data; K. Grubb, B. Spano, and N. Wheeler, personal communication). ...
Interspecific interactions can play an essential role in shaping wildlife populations and communities. To date, assessments of interspecific interactions, and more specifically predator–prey dynamics, in aquatic systems over broad spatial and temporal scales (i.e., hundreds of kilometers and multiple years) are rare due to constraints on our abilities to measure effectively at those scales. We applied new methods to identify space‐use overlap and potential predation risk to Atlantic tarpon (Megalops atlanticus) and permit (Trachinotus falcatus) from two known predators, great hammerhead (Sphyrna mokarran) and bull (Carcharhinus leucas) sharks, over a 3‐year period using acoustic telemetry in the coastal region of the Florida Keys (USA). By examining spatiotemporal overlap, as well as the timing and order of arrival at specific locations compared to random chance, we show that potential predation risk from great hammerhead and bull sharks to Atlantic tarpon and permit are heterogeneous across the Florida Keys. Additionally, we find that predator encounter rates with these game fishes are elevated at specific locations and times, including a prespawning aggregation site in the case of Atlantic tarpon. Further, using machine learning algorithms, we identify environmental variability in overlap between predators and their potential prey, including location, habitat, time of year, lunar cycle, depth, and water temperature. These predator–prey landscapes provide insights into fundamental ecosystem function and biological conservation, especially in the context of emerging fishery‐related depredation issues in coastal marine ecosystems.
... Most-probable tracks were then estimated using the tag manufacturer's software that utilizes a hidden Markov model (Pedersen et al., 2011; WC-GPE3, Wildlife Computers), and considers transmitted light level, temperature and depth data alongside sea surface temperature (SST; NOAA OI SST V2 High Resolution) and bathymetric constraints (ETOPO1-Bedrock). This method calculates a posterior probability distribution that estimates two maximum likelihood position estimates per day (Skomal et al., 2017). The diffusion parameter was set to 3 ms −1 (Block et al., 2011) to govern the allowable distance moved per day. ...
Over the last two decades, satellite tagging of adult and sub-adult white sharks Carcharodon carcharias off the west coast of North America has revealed a predictable onshore-offshore migratory cycle. Our current understanding of the vertical movements exhibited by white sharks while in their coastal foraging phase in the California Current, however, remains limited. Here, we used recovered datasets from 31 archival satellite tags to quantify vertical habitat use. Tags were deployed on individuals between 2000 and 2018 and recorded depth and temperature data at continuous 1–120 s intervals before being recovered up to a year after deployments. Four satellite-tagged individuals were concurrently tagged with acoustic tags, providing precise location data when detected by acoustic receivers that allowed us to explore how reported vertical habitat use varied spatially. While in the coastal shelf waters, white sharks moved at a mean depth ± SD of 14.3 ± 4.0 m and occupied significantly deeper depths during the day than the night. High individual, temporal and spatial variation was evident in vertical movements, while consistent diel and lunar effects emphasized the importance of light-level driving vertical behavior around hunting sites. The vertical movement behaviors reported here provide knowledge of how white sharks may directly and indirectly interact with their mammalian prey in a dynamic three-dimensional system during their capital foraging phase. Temporal patterns in vertical behavior, for instance, indicated that surface waters during early morning hours are the riskiest place for prey. Combining these novel findings with higher-resolution biologging techniques in future studies will allow us to further contextualize fine-scale vertical movement behaviors of white sharks and examine the specific foraging events that could not yet be isolated in the tagging data.
... In New South Wales, Australia, white sharks are caught, relocated ∼1 km offshore, and released through a non-lethal mitigation approach using Shark-Management-Alert-in-Real-Time (SMART) drumlines (Tate et al., 2021a), yet their behavioral responses to capture, and hence the implications of this strategy for both sharks and people, are unknown. Although white sharks' broad scale movements have been the subject of several studies (Jorgensen et al., 2010;Skomal et al., 2017;Spaet et al., 2020a,b;Lee et al., 2021), knowledge of their fine scale behavior remains restricted to a few specific contexts (e.g., foraging near seal colonies; Jewell et al., 2019;Semmens et al., 2019;Watanabe et al., 2019a,b). A more detailed understanding of both their post-capture responses and natural behavior across ecological contexts is thus critical to their management and conservation. ...
Multisensor biologging provides a powerful tool for ecological research, enabling fine-scale observation of animals to directly link physiology and movement to behavior across ecological contexts. However, applied research into behavioral disturbance and recovery following human interventions (e.g., capture and translocation) has mostly relied on coarse location-based tracking or unidimensional approaches (e.g., dive profiles and activity/energetic metrics) that may not resolve behaviors and recovery processes. Biologging can improve insights into both disturbed and natural behavior, which is critical for management and conservation initiatives, although challenges remain in objectively identifying distinct behavioral modes from complex multisensor datasets. Using white sharks (Carcharodon carcharias) released from a non-lethal catch-and-release shark bite mitigation program, we explored how combining multisensor biologging (video, depth, accelerometers, gyroscopes, and magnetometers), track reconstruction and behavioral state modeling using hidden Markov models (HMMs) can improve our understanding of behavioral processes and recovery. Biologging tags were deployed on eight white sharks, recording their continuous behaviors, movements, and environmental context (habitat, interactions with other organisms/objects) for periods of 10–87 h post-release. Dive profiles and tailbeat analysis (as a standard, activity-based method for assessing recovery) indicated an immediate “disturbed” period of offshore movement, displaying rapid tailbeats and an average tailbeat-derived recovery period of 9.7 h, with evidence of smaller individuals having longer recoveries. However, further integrating magnetometer-derived headings, track reconstruction and HMM modeling revealed a cryptic shift to diurnal clockwise-counterclockwise circling behavior, which we argue represents compelling new evidence for hypothesized unihemispheric sleep amongst elasmobranchs. By simultaneously providing critical information toward conservation-focused shark management and understudied aspects of shark behavior, our study highlights how integrating multisensor information through HMMs can improve our understanding of both post-release and natural behavior, especially in species that are difficult to observe directly.
... Adult white sharks (Carcharodon carcharias) are distributed mostly in offshore pelagic waters, including oceanic islands (Klimley et al., 1992;Domeier and Nasby-Lucas, 2007;Jorgensen et al., 2010;Francis et al., 2015;Boldrocchi et al., 2017;Skomal et al., 2017;Moro et al., 2020), while juveniles occupy coastal areas as nurseries (Bruce and Bradford, 2012;Harasti et al., 2017;Curtis et al., 2018;Bruce et al., 2019). In the northeast Pacific, newborn, young of the year, and juvenile white shark occupy coastal areas until they become sub-adults and can migrate between spatially separate nurseries (Klimley et al., 1992;Dewar et al., 2004;Weng et al., 2007Weng et al., , 2012Lowe et al., 2012;Oñate-González et al., 2017;White et al., 2019). ...
Knowledge about top predators’ trophic ecology is crucial for defining their role in ecosystems, understanding habitat preferences, characterizing life stage-specific feeding habits, and evaluating their interaction with fisheries. In the northeastern Pacific, white sharks (Carcharodon carcharias) occupy coastal habitats during the early life stages, including Bahía Sebastián Vizcaíno (BSV) in Mexico, which is a known nursery area. Although BSV presumably provides high prey abundance, the trophic ecology of immature white sharks is poorly understood. Carbon and nitrogen bulk stable isotope analyses (SIA) were used to explore the trophic relationship of early life stages with their potential prey and to infer dietary overlap with sympatric sharks, while SIA of amino acids were used to estimate trophic position. Muscle samples from young white sharks and inshore demersal prey commonly found in their stomach contents were sampled. Demersal prey and literature-derived isotope ratios for pelagic and offshore species were incorporated into mixing models with a Bayesian framework to estimate their contribution to white shark tissues. Nearshore demersal prey had the highest contribution for all life stages (between 35 and 47%), consistent with previous reports based on gut content analysis. The contribution of pelagic (between 26 and 37%) and offshore (between 14 and 32%) prey was smaller and suggests potential periodic changes in foraging grounds and the presence of a maternal-derived isotopic signature. A high contribution of demersal prey indicates a high level of interaction with local fisheries that target those species and catch white sharks incidentally and is consistent with immature shark movement patterns. Isotope ratios of two sympatric sharks, smooth hammerhead Sphyrna zygaena and copper sharks Carcharhinus brachyurus, were used to estimate the overlap in isotopic niche space. Immature white sharks had the smallest isotopic niche, while the highest was for copper sharks. Overlap was greatest between white sharks and hammerheads (∼45%), while overlap with copper sharks was limited (<20%), suggesting less potential for competition. Trophic position estimates were similar to those previously reported for the species. These results highlight the importance of coastal demersal prey heavily targeted by local fisheries for the diet of young white sharks and support the importance of BSV as a nursery habitat.
... However, it is not yet known whether this is due to seasonal changes in temperature, changing foraging opportunities or mating site selection. White shark migrations include transoceanic, as well as long-distance coastal migrations (Bonfil et al., 2005;Skomal et al., 2017). Those tracked in this study were primarily tagged off Massachusetts, a known foraging ground, south of the New York Bight nursery area (Curtis et al., 2018). ...
Data from the Integrated Tracking of Aquatic Animals in the Gulf of Mexico (iTAG) network, and sister networks, were used to evaluate fish movements in the Florida Keys—an extensive reef fish ecosystem just north of Cuba connecting the Atlantic Ocean and Gulf of Mexico. We analysed ~2 million detections for 23 species, ranging from reef fish such as Nassau grouper (Epinephelus striatus, Serranidae) to migratory apex predators such as white sharks (Carcharodon carcharias, Lamnidae). To facilitate comparisons across species, we used an eco-evolutionary movement strategy framework that identified measurable movement traits and their proximate and ultimate drivers. Detectability was species-specific and quantified with a detection potential index. Life stages detected in the study area varied by species and residency varied with life stage. Four annual movement types were identified as follows: high site-fidelity residents, range residents, seasonal migrants and general migrants. The endangered smalltooth sawfish (Pristis pectinata, Pristidae), a seasonal migrant, exhibited the greatest within-ecosystem connectivity. Site attachment, stopover and deep-water migration behaviours differed between individuals, species and annual movement types. All apex predators were migratory. General migrants were significantly larger than fish in the other movement types, a life-history and movement trait combination that is common but not exclusive, as many small pelagics also migrate. Most teleosts exhibited movements associated with spawning. As concerns grow over habitat and biodiversity loss, multispecies movescapes, such as presented here, are expected to play an increasingly important role in informing ecosystem-based and non-extractive fisheries management strategies.
... White sharks (Carcharodon carcharias) are a circumglobally distributed marine top predator currently listed as Vulnerable on the IUCN Red List of Threatened Species (IUCN, 2019). Electronic tagging studies indicate migratory behavior on the scale of ocean basins but high site fidelity in which individuals aggregate repeatedly in predictable coastal locations (Bruce et al., 2006;Domeier and Nasby-Lucas, 2008;Jorgensen et al., 2010;Skomal et al., 2017;Weng et al., 2007). Genetic evidence suggests natal philopatry (Jorgensen et al., 2010) resulting in discrete population structure, with clearly defined population segments such as South Africa (Pardini et al., 2000), Australia-New Zealand (Blower et al., 2012), northeast Pacific (Jorgensen et al., 2010) northwest Pacific (Tanaka et al., 2011), Mediterranean (Gubili et al., 2010) and northwest Atlantic (O'Leary et al., 2015). ...
Determining population trends is critical for evaluating management actions and prioritizing species protections. In this study, we used empirical data to produce an estimate of the population trend for sub-adult and adult white sharks in central California. We used the unique dorsal fin morphology to build a mark-recapture data set in a modified Jolly-Seber model (POPAN formulation) to estimate annual abundance and then investigate population growth rates using parametric bootstrapping methods for sub-adult and adult sharks (males and females). For all demographic groups combined, we found equivocal evidence for a positive regional population growth (λ = 1.07 (95% CI = 0.91 to 1.23)). However, sex- and size-specific population growth rate estimates provided some evidence of population increases for reproductively mature males (λ = 1.06 (95% CI = 0.99 to 1.13)) and females (λ = 1.06 (95% CI = 0.95 to 1.17)). For sub-adult male and female white sharks, point estimates of λ were positive but uncertainty prevents strong inference (λ = 1.07 (95% CI = 0.85 to 1.29)) and (λ = 1.08 (95% CI = 0.88 to 1.28)), respectively. Our findings of a potential increase in reproductive-aged white sharks in central California may be a result of regional fluxes in density or attributed in part to current protection efforts and subsequent increase in abundance of pinnipeds as well as reduced gill-net fisheries mortality of juveniles. A trend estimate for the entire northeastern Pacific will require obtaining similar data across known aggregation areas along the west coast of North America.
Context. Our understanding of population- and ecosystem-level processes commonly considers conspecific individuals to be ecologically equivalent. However, individuals of the same species may use resources differently, supporting the prevalence of individual specialisation or ‘apparent specialisation’. Individuals within a geographically defined population may also exhibit complex subpopulation movements, whereby individuals show philopatry to specific regions that further drives individual variation. Aims. White sharks (Carcharodon carcharias) are top predators in temperate to tropical ecosystems. In Australia, two discrete subpopulations of white sharks (an east and a southwest subpopulation) have been proposed based on genetics and limited movement across Bass Strait. We aimed to characterise the extent of ontogenetic divergence in resource–habitat behaviour of white sharks from both regions. Methods. We used high-resolution retrospective stable isotope profiles (δ15Nand δ13C) of 74 white shark vertebral centra to examine ontogenetic trophic–habitat signatures for individuals sampled from both regions. Key results. Our results demonstrate isotopic separation between juvenile–subadult sharks sampled east (−13.7 ± 0.72 δ13C; 14.2 ± 0.8 δ15N, n = 47) and southwest (−14.4 ± 0.6 δ13C; 12.5 ± 1.2 δ15N, n = 27) of Bass Strait, but with strong oscillatory trends across both regions, likely related to seasonal movements. Relative individual niche width revealed apparent specialised behaviour of juvenile–subadult sharks within both regions. Conclusions. Retrospective ontogenetic isotopic profiles of vertebrae from Australian white sharks provide evidence to support an ecological two-population model for juvenile and subadult life stages. Implications. Given many marine top predators are undergoing systematic population declines, understanding individual variation in diet and movement in the context of population structure and true or apparent specialisation is central to elucidating their ecological roles.
The porbeagle shark Lamna nasus , a top predator in the North Atlantic, is vulnerable to anthropogenic stressors due to its life history characteristics. Understanding its biology, abundance and spatial ecology is crucial for underpinning effective conservation and management strategies. We collected satellite tag data from 10 porbeagle sharks caught off the north coast of Ireland to study migration behaviour and space use. Data from pop-up satellite archival tags and platform terminal telemetry tags collected between July 2010 and February 2014 (for deployments up to ~9 mo) showed long-distance (1479-25707 km), seasonal migrations, with autumnal movements along the shelf-break to regions around Portugal, the Bay of Biscay and the Azores via the Mid-Atlantic ridge. Migrations to waters off Norway and the Faroe/Shetland Islands were also evident prior to these autumnal southward migrations. In spring, some sharks returned northwards, and there was evidence of site fidelity for shelf waters around the northern Irish coast and western Scotland and the Celtic Sea in summer. Porbeagles exhibited seasonal changes in vertical space use as they traversed various habitats during migration, with deeper occupancy of the water column in winter than in summer. There was a distinct day-night pattern in porbeagle depth distribution during their off-shelf residency in winter, consistent with diel vertical migrations between deep waters in daytime and the surface layers at night. Nocturnal depth distribution was closely associated with the lunar cycle, with deeper residency/diving occurring during periods of full moon. Porbeagles occupied and traversed both the open ocean and coastal areas of high fishing activity, highlighting the challenge of managing this stock because of large-scale migratory behaviour.
The occurrence of white sharks, Carcharodon carcharias, in Ecuadorian waters has been based on informal reports and questionable circumstantial evidence. We reviewed unique video evidence from a commercial tuna purse seiner and confirmed the first record for this apex predator within Ecuadorian waters and one of the few available for the Tropical Eastern Pacific. It is hypothesized that the oceanography resulting from the 2021 La Niña ENSO event may be related to this unusual sighting. We propose a vagrant status for the Galapagos Islands until further evidence can confirm residency.
Tectonic changes in the Southern Ocean likely triggered global cooling across the Eocene, yet the evidence for when the Drake Passage opened remains ambiguous. This climatic-tectonic change likely impacted marine ecosystems, including sharks that inhabited high-latitude regions. The fossil record could provide insights into sharks' response to global cooling over the Eocene, but paleoecological studies are few. The Middle-to-Late Eocene units on Seymour Island provide a rich, diverse fossil record, including that of sharks. We analyzed the oxygen isotope composition of phosphate from shark tooth bioapatite (δ 18 Op) and compared to results of co-occurring bivalves and predictions from an isotope-enabled global climate model output to investigate habitat use and environmental conditions. Bulk δ 18 Op values (mean 22.0 ± 1.3) exceeds that in simulated seasonal and regional values. Pelagic and benthic taxa exhibit similar values across units but are offset relative to bivalve and modeled δ 18 Op values. Some taxa suggest movements into warmer water (e.g., Otodus) or deeper, colder waters (e.g., Pristiophorus). Taxa like Raja and Squalus display no shift, tracking seasonal signals in Seymour Island. The lack of difference in δ 18 Op values between pelagic and benthic sharks in the Late Eocene likely indicates that sharks ventured as far as the Drake Passage. Our findings demonstrate that sharks usually track preferred conditions in their tooth bioapatite instead of acting as passive tracers that record environmental signals in a single location.
Climate change influences marine environmental conditions and is projected to increase future environmental variability. In the North Atlantic, such changes will affect the behavior and spatiotemporal distributions of large pelagic fish species (i.e., tunas, billfishes, and sharks). Generally, studies on these species have focused on specific climate-induced changes in abiotic factors separately (e.g., water temperature) and on the projection of shifts in species abundance and distribution based on these changes. In this review, we consider the latest research on spatiotemporal effects of climate-induced environmental changes to HMS’ life history, ecology, physiology, distribution, and habitat selection, and describe how the complex interplay between climate-induced changes in biotic and abiotic factors, including fishing, drives changes in species productivity and distribution in the Northwest Atlantic. This information is used to provide a baseline for investigating implications for management of pelagic longline fisheries and to identify knowledge gaps in this region. Warmer, less oxygenated waters may result in higher post-release mortality in bycatch species. Changes in climate variability will likely continue to alter the dynamics of oceanographic processes regulating species behavior and distribution, as well as fishery dynamics, creating challenges for fishery management. Stock assessments need to account for climate-induced changes in species abundance through the integration of species-specific responses to climate variability. Climate-induced changes will likely result in misalignment between current spatial and temporal management measures and the spatiotemporal distribution of these species. Finally, changes in species interactions with fisheries will require focused research to develop best practices for adaptive fisheries management and species recovery.
Satellite telemetry as a tool in marine ecological research continues to adapt and grow and has become increasingly popular in recent years to study shark species on a global scale. A review of satellite tag application to shark research was published in 2010, provided insight to the advancements in satellite shark tagging, as well as highlighting areas for improvement. In the years since, satellite technology has continued to advance, creating smaller, longer lasting, and more innovative tags, capable of expanding the field. Here we review satellite shark tagging studies to identify early successes and areas for rethinking moving forward. Triple the amount of shark satellite tagging studies have been conducted during the decade from 2010 to 2020 than ever before, tracking double the number of species previously tagged. Satellite telemetry has offered increased capacity to unravel ecological questions including predator and prey interactions, migration patterns, habitat use, in addition to monitoring species for global assessments. However, <17% of the total reviewed studies directly produced results with management or conservation outcomes. Telemetry studies with defined goals and objectives produced the most relevant findings for shark conservation, most often in tandem with secondary metrics such as fishing overlap or management regimes. To leverage the power of telemetry for the benefit of shark species, it remains imperative to continue improvements to tag function and maximize the outputs of tagging efforts including increasing data sharing capacity and standardization across the field, as well as spatial and species coverage. Ultimately, this review offers a status report of shark satellite tagging and the ways in which the field can continue to progress.
A list of diadromous and marine fishes occurring in the Saint-Pierre and Miquelon archipelago and its EEZ has been compiled from various available data sources: collections, local and international databases, and literature. This belated work was needed as the only existing checklist dates back to the 19th century and FishBase, as of early 2022, provided a list of only 14 species, and 81 in the French taxonomic register TAXREF. The list assembled here covers 122 species, of which 111 are marine fishes, assigned to 103 genera and 66 families. This list is not comprehensive, but it constitutes a first reference, to be updated with new information.
Despite its consequences for ecological processes and population dynamics, intra-specific variability is frequently overlooked in animal movement studies. Consequently, the necessary resolution to reveal drivers of individual movement decisions is often lost as animal movement data are aggregated to infer average or population patterns. Thus, an empirical understanding of why a given movement pattern occurs remains patchy for many taxa, especially in marine systems. Nonetheless, movement is often rationalized as being driven by basic life history requirements, such as acquiring energy (feeding), reproduction, predator-avoidance, and remaining in suitable environmental conditions. However, these life history requirements are central to every individual within a species and thus do not sufficiently account for the high intra-specific variability in movement behavior and hence fail to fully explain the occurrence of multiple movement strategies within a species. Animal movement appears highly context dependent as, for example, within the same location, the behavior of both resident and migratory individuals is driven by life history requirements, such as feeding or reproduction , however different movement strategies are utilized to fulfill them. A systematic taxa-wide approach that, instead of averaging population patterns, incorporates and utilizes intra-specific variability to enable predictions as to which movement patterns can be expected under a certain context, is needed. Here, we use intra-specific variability in elasmobranchs as a case study to introduce a stepwise approach for studying animal movement drivers that is based on a context-dependence framework. We examine relevant literature to illustrate how this context-focused approach can aid in reliably identifying drivers of a specific movement pattern. Ultimately, incorporating behavioral variability in the study of movement drivers can assist in making predictions about behavioral responses to environmental change, overcoming tagging biases, and establishing more efficient conservation measures.
Assessing progress for the endangered white shark (Carcharodon carcharias) relative to Canadian conservation objectives requires understanding distribution patterns. From the largest tagging data set in the Northwest Atlantic (2010–2020; 272 deployments), we determined the proportion of the population detected in Canadian waters, characterized patterns in occupancy, and explored the behavioural characteristics of animals while in Canadian waters versus elsewhere in their range. The component of the population detected in Canadian waters annually was highly variable, yet proportionately small. Juveniles and subadults were 4.7 and 3.4 times more likely, respectively, to move northward than adults. From June to November, all pop-up satellite archival tagged white sharks remained primarily in coastal locations within the 200 m bathymetric contour and exhibited shallow diving behaviour within the top 100 m of the water column. However, individuals in Canadian waters experienced a more restricted temperature range and used proportionately less of the water column. Accounting for behavioural effects on distribution when predicting habitat use from environmental associations will become critical to evaluate the population-level impact of recovery actions implemented under Canadian legislation.
Greater amberjack (Seriola dumerili) is an important fishery resource with a circumglobal distribution from tropical to temperate waters. Here, we investigated the spawning migration and habitat utilization of S. dumerili in the East China Sea (ECS). Archival tags were attached to 22 adult fish to examine their horizontal and vertical movements and estimate the spawning ground. S. dumerili were captured and released in the coastal waters of eastern Taiwan on November of 2016 and 2017. Information from seven pop‐up satellite archival tags and seven depth–temperature recorders was recovered. Almost all of the fish stayed in the Taiwanese exclusive economic zone. Most individuals moved from released site to the southern edge of the ECS and showed behavior associated with the topographic features in winter (November to December). These phenomena may be related to foraging and be driven by oceanographic features such as the seasonal monsoon and the Kuroshio. The fish then migrated to the south offshore area of Taiwan in January and February. During their southward migration, the fish experienced a slowly elevated water temperature regime (SETR), which is one of the environmental factors that induce final oocyte maturation. In the spawning season (February to April), tagged females exhibited continuous diel vertical movements (DVMs) after experiencing the SETR. These continuous DVMs were observed over a wide geographic range from north to south in the Kuroshio off eastern Taiwan. Our study demonstrated that the putative spawning ground of S. dumerili must extend further in a north–south direction than predicted in a previous study.
Even species within the same assemblage have varied responses to climate change, and there is a poor understanding for why some taxa are more sensitive to climate than others. In addition, multiple mechanisms can drive species’ responses, and responses may be specific to certain life stages or times of year. To test how marine species respond to climate variability, we analyzed 73 diverse taxa off the southeast U.S. coast in 26 years of scientific trawl survey data and determined how changes in distribution and biomass relate to temperature. We found that winter temperatures were particularly useful for explaining interannual variation in species’ distribution and biomass, though the direction and magnitude of the response varied among species from strongly negative, to little response, to strongly positive. Across species, the response to winter temperature varied greatly, with much of this variation being explained by thermal preference. A separate analysis of annual commercial fisheries landings revealed that winter temperatures may also impact several important fisheries in the southeast U.S. Based on the life stages of the species surveyed, winter temperature appears to act through overwinter mortality of juveniles or as a cue for migration timing. We predict that this assemblage will be responsive to projected increases in temperature, and that winter temperature may be broadly important for species relationships with climate on a global scale. This article is protected by copyright. All rights reserved.
Spatial segregation of animals by class (i.e. maturity or sex) within a population due to differential rates of temporary emigration (TE) from study sites can be an important life history feature to consider in population assessment and management. However, such rates are poorly known; new quantitative approaches to address these knowledge gaps are needed. We present a novel application of multi-event models that takes advantage of two sources of detections to differentiate temporary emigration from apparent absence to quantify class segregation within a study population of double-marked (photo-identified and tagged with coded acoustic transmitters) white sharks (Carcharodon carcharias) in central California. We use this model to test if sex-specific patterns in TE result in disparate apparent capture probabilities (po) between male and female white sharks, which can affect the observed sex ratio. The best-supported model showed a contrasting pattern of Pr(TE) from coastal aggregation sites between sexes (for males Pr(TE) =0.015 (95% CI=0.00, 0.31) and Pr(TE) =0.57 (0.40, 0.72) for females), but not maturity classes. Additionally, by accounting for Pr(TE) and imperfect detection, we were able to estimate class-specific values of true capture probability (p*) for tagged and untagged sharks. The best-supported model identified differences between maturity classes but no difference between sexes or tagging impacts (tagged mature sharks p*=0.55 (0.46-0.63) and sub-adult sharks p*= 0.36 (0.25, 0.50); and untagged mature sharks p*=0.50 (0.39-0.61) and sub-adults p*=0.18 (0.10, 0.31). Estimated sex-based differences in po were linked to sex-specific differences in Pr(TE) but not in p*; once the Pr(TE) is accounted for, the p* between sexes was not different. These results indicate that the observed sex ratio is not a consequence of unequal detectability and sex-specific values of Pr(TE) are important drivers of the observed male-dominated sex ratio. Our modeling approach reveals complex class-specific patterns in Pr(TE) and p* in a mark-recapture data set, and highlights challenges for the population modeling and conservation of white sharks in central California. The model we develop here can be used to estimate rates of temporary emigration and class segregation when two detection methods are used. This article is protected by copyright. All rights reserved.
Comprehension of ecological processes in marine animals requires information regarding dynamic vertical habitat use. While many pelagic predators primarily associate with epipelagic waters, some species routinely dive beyond the deep scattering layer. Actuation for exploiting these aphotic habitats remains largely unknown. Recent telemetry data from oceanic whitetip sharks (Carcharhinus longimanus) in the Atlantic show a strong association with warm waters (>20°C) less than 200 m. Yet, individuals regularly exhibit excursions into the meso- and bathypelagic zone. In order to examine deep-diving behavior in oceanic whitetip sharks, we physically recovered 16 pop-up satellite archival tags and analyzed the high-resolution depth and temperature data. Diving behavior was evaluated in the context of plausible functional behavior hypotheses including interactive behaviors, energy conservation, thermoregulation, navigation, and foraging. Mesopelagic excursions (n = 610) occurred throughout the entire migratory circuit in all individuals, with no indication of site specificity. Six depth-versus-time descent and ascent profiles were identified. Descent profile shapes showed little association with examined environmental variables. Contrastingly, ascent profile shapes were related to environmental factors and appear to represent unique behavioral responses to abiotic conditions present at the dive apex. However, environmental conditions may not be the sole factors influencing ascents, as ascent mode may be linked to intentional behaviors. While dive functionality remains unconfirmed, our study suggests that mesopelagic excursions relate to active foraging behavior or navigation. Dive timing, prey constituents, and dive shape support foraging as the most viable hypothesis for mesopelagic excursions, indicating that the oceanic whitetip shark may regularly survey extreme environments (deep depths, low temperatures) as a foraging strategy. At the apex of these deep-water excursions, sharks exhibit a variable behavioral response, perhaps, indicating the presence or absence of prey.
The white shark, Carcharodon carcharias, is both one of the largest apex predators in the world and among the most heavily protected marine fish. Population genetic diversity is in part shaped by recent demographic history and can thus provide information complementary to more traditional population assessments, which are difficult to obtain for white sharks and have at times been controversial. Here, we use the mitochondrial control region and 14 nuclear-encoded microsatellite loci to assess white shark genetic diversity in 2 regions: the Northwest Atlantic (NWA, N = 35) and southern Africa (SA, N = 131). We find that these 2 regions harbor genetically distinct white shark populations (Φ ST = 0.10, P < 0.00001; microsatellite F ST = 0.1057, P < 0.021). M-ratios were low and indicative of a genetic bottleneck in the NWA (M-ratio = 0.71, P < 0.004) but not SA (M-ratio = 0.85, P = 0.39). This is consistent with other evidence showing a steep population decline occurring in the mid to late 20th century in the NWA, whereas the SA population appears to have been relatively stable. Estimates of effective population size ranged from 22.6 to 66.3 (NWA) and 188 to 1998.3 (SA) and evidence of inbreeding was found (primarily in NWA). Overall, our findings indicate that white population dynamics within NWA and SA are determined more by intrinsic reproduction than immigration and there is genetic evidence of a population decline in the NWA, further justifying the strong domestic protective measures that have been taken for this species in this region. Our study also highlights how assessment of genetic diversity can complement other sources of information to better understand the status of threatened marine fish populations.
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Age and growth estimates for the white shark (Carcharodon carcharias) in the western North Atlantic Ocean (WNA) were derived from band pair counts on the vertebral centra of 81 specimens collected between 1963 and 2010. We used two previously published criteria to interpret band pairs and assessed the validity of each method using Δ¹⁴C levels from a recent bomb radiocarbon validation study and existing Δ¹⁴C reference chronologies in the WNA. Although both criteria produced age estimates consistent, to varying degrees, with different reference chronologies, only one was considered valid when life history information was used to select the appropriate reference chronology and minimum/maximum ages based on bomb carbon values were taken into consideration. These age estimates, validated up to 44 years, were used to develop a growth curve for the species, which was best described using the Schnute general model (sexes combined). These results indicate that white sharks grow more slowly and live longer than previously thought.
Spatially-explicit habitat models can impart a scientific basis for delineating critical habitats that relate species' distributions to physical and biological conditions, even in marine environments with vague and dynamic boundaries. We developed a habitat model of the relationship between the winter distribution of North Atlantic right whales Eubalaena glacialis, one of the most endangered large whales in the world, and environmental characteristics in its only identified calving ground, the waters off Florida and Georgia. Our objective was to provide a scientific basis for revising critical habitat boundaries in the southeastern USA (SEUS) and to predict potential habitat in the mid-Atlantic region north of the study area through a better understanding of the relationship of observed right whale distribution to environmental conditions. A long-term data set of right whale sightings from aerial surveys within the SEUS (conducted seasonally, December through March, from 1992/1993 to 2000/2001) was used in a generalized additive model to eval u -ate right whale distribution in relation to sea surface temperature, bathymetry, wind data, and several spatial variables. Model results indicated that sea surface temperature and water depth were significant predictors of calving right whale spatial distribution. The habitat relationships were unimodal, with peak sighting rates occurring at water temperatures of 13 to 15 oC and water depths of 10 to 20 m. Model results indicated areas of potentially important calving habitat outside currently defined critical habitat. Our semi-monthly predicted distributions, based on model results, provide managers with a range of scientifically based choices for revising critical habitat boundaries to achieve the desired level of protection. Predictions extrapolated through the mid-Atlantic suggested appropriate habitat features north of the study site, although analysis of data from more recent surveys in this region would be required to validate model results.
The coastal migratory stock of Striped Bass Morone saxatilis has supported fisheries off the Massachusetts (MA) coast for centuries. However, despite this historical importance, limited information is available regarding Striped Bass seasonal movement patterns or migratory pathways within MA coastal waters and beyond. Using passive acoustic telemetry, we evaluated the seasonal residency, coastal migration, and stock composition of 159 adult Striped Bass (65–110 cm TL) by using a network of fixed acoustic receivers deployed from 2008 to 2012 in MA coastal waters and along the U.S. East Coast as part of the Atlantic Cooperative Telemetry (ACT) Network. Seasonal monitoring of tagged individuals indicated that adult Striped Bass were present in MA coastal waters north of Cape Cod annually during May–November, moving into and out of the region via the Cape Cod Canal and along the east side of Cape Cod. Of the 159 tagged individuals, 125 (79%) were detected outside of MA coastal waters by the ACT Network and were observed to make seasonal migrations along the coast to overwintering areas of the mid‐Atlantic and major spawning areas (Chesapeake Bay, Delaware River, and Hudson River). Numerous tagged individuals exhibited interannual fidelity to summer foraging habitat in MA coastal waters, returning to the region for up to 2 years after tagging. Detection of tagged individuals in known spawning areas revealed that Striped Bass from each major stock were present within MA coastal waters during the summer months, with the Chesapeake Bay stock appearing to be the largest contributor to the population from 2008 to 2010. Collectively, these observations suggest that the seasonal population of adult Striped Bass in MA coastal waters has a diversity of origins, demonstrating the importance of the health of each spawning component to the MA seasonal fishery.
Received October 11, 2013; accepted January 23, 2014
Despite recent advances in field research on white sharks (Carcharodon carcharias) in several regions around the world, opportunistic capture and sighting records remain the primary source of information on this species in the northwest Atlantic Ocean (NWA). Previous studies using limited datasets have suggested a precipitous decline in the abundance of white sharks from this region, but considerable uncertainty in these studies warrants additional investigation. This study builds upon previously published data combined with recent unpublished records and presents a synthesis of 649 confirmed white shark records from the NWA compiled over a 210-year period (1800-2010), resulting in the largest white shark dataset yet compiled from this region. These comprehensive records were used to update our understanding of their seasonal distribution, relative abundance trends, habitat use, and fisheries interactions. All life stages were present in continental shelf waters year-round, but median latitude of white shark occurrence varied seasonally. White sharks primarily occurred between Massachusetts and New Jersey during summer and off Florida during winter, with broad distribution along the coast during spring and fall. The majority of fishing gear interactions occurred with rod and reel, longline, and gillnet gears. Historic abundance trends from multiple sources support a significant decline in white shark abundance in the 1970s and 1980s, but there have been apparent increases in abundance since the 1990s when a variety of conservation measures were implemented. Though the white shark's inherent vulnerability to exploitation warrants continued protections, our results suggest a more optimistic outlook for the recovery of this iconic predator in the Atlantic.
With a current estimate of ~1,000 million tons, mesopelagic fishes likely dominate the world total fishes biomass. However, recent acoustic observations show that mesopelagic fishes biomass could be significantly larger than the current estimate. Here we combine modelling and a sensitivity analysis of the acoustic observations from the Malaspina 2010 Circumnavigation Expedition to show that the previous estimate needs to be revised to at least one order of magnitude higher. We show that there is a close relationship between the open ocean fishes biomass and primary production, and that the energy transfer efficiency from phytoplankton to mesopelagic fishes in the open ocean is higher than what is typically assumed. Our results indicate that the role of mesopelagic fishes in oceanic ecosystems and global ocean biogeochemical cycles needs to be revised as they may be respiring ~10% of the primary production in deep waters.
Conservation and management efforts for white sharks (Carcharodon carcharias) remain hampered by a lack of basic demographic information including age and growth rates. Sharks are typically aged by counting growth bands sequentially deposited in their vertebrae, but the assumption of annual deposition of these band pairs requires testing. We compared radiocarbon (Δ(14)C) values in vertebrae from four female and four male white sharks from the northwestern Atlantic Ocean (NWA) with reference chronologies documenting the marine uptake of (14)C produced by atmospheric testing of thermonuclear devices to generate the first radiocarbon age estimates for adult white sharks. Age estimates were up to 40 years old for the largest female (fork length [FL]: 526 cm) and 73 years old for the largest male (FL: 493 cm). Our results dramatically extend the maximum age and longevity of white sharks compared to earlier studies, hint at possible sexual dimorphism in growth rates, and raise concerns that white shark populations are considerably more sensitive to human-induced mortality than previously thought.
Background
Satellite tagging programs have provided detailed information about the migratory patterns of northeastern Pacific white sharks, revealing a seasonal migration between a vast offshore region and coastal aggregation sites. Although adult males undergo annual round-trip migrations, photo-identification programs have noted that sexually mature females may only visit coastal aggregation sites once every 2 years, a behavior that is presumably linked to an estimated 18-month gestation period. The whereabouts of females during their full 2-year migration were previously unknown, because of the limited battery capacity of satellite pop-up tags.
Results
Through the use of satellite-linked radio-telemetry tags with multi-year tracking capability, we describe the 2-year migratory pattern for four mature female white sharks tagged at Guadalupe Island, Mexico. The 2-year migration comprised four phases: 1) an Offshore Gestation Phase (which had an average duration of 15.5 months; 2) a Pupping Phase, which occurred along the Mexican coast between the months of April and August; 3) a Pre-Aggregation Phase (when the females were in transition between the Pupping Phase and Guadalupe Island; and 4) the Guadalupe Island Aggregation Phase, which began when the mature females arrived at Guadalupe Island between late September and early October.
Conclusions
Long-term satellite tracking of mature female white sharks highlighted the connectivity between a single presumed mating site at Guadalupe Island, and two widely separated pupping sites along the Mexican coast. The Offshore Gestation Phase provided evidence that the females remained offshore for up to 16 months during their 2-year migration cycle. The Pupping Phase along the Mexican coast coincided with the seasonal presence of young-of-the-year white sharks along the coast of North America, and with a presumed gestation period of 18 months, this placed mating between October and January, during the period when white sharks are known to be at Guadalupe Island. Tracking data during the time sharks were offshore showed that mature males and females are spatially segregated, except for their concurrent seasonal presence at Guadalupe Island. These discoveries provide important new details about the complete life history of northeastern Pacific white sharks while identifying crucial regions in which young-of-the-year, juveniles and adult females are most vulnerable.
The white shark, a top predator inhabiting the world’s oceans, is an endangered species. However, knowledge of its life-history traits and population structure is still limited. We hypothesised that life-history traits would vary among populations because the species’ various habitats are diverse and change through time. Age was estimated by counting growth bands in the centra of white sharks caught in Japan. The von Bertalanffy growth parameters were estimated at L∞ = 455 cm TL, k = 0.196 year–1 and t0 = –1.92 years for males and L∞ = 607 cm TL, k = 0.159 year–1 and t0 = –1.80 years for females. The growth rate to maturity was higher than that known for individuals from California and South Africa. Male sharks matured at 310 cm TL at 4 years of age and females began to mature at ~450 cm TL and 7 years. The D-loop-region sequences of mitochondrial DNA extracted from Japanese white sharks and GenBank datasets from sharks of California, Australia, New Zealand and South Africa indicate that Japanese white sharks form a monophyletic clade separate from the populations of other regions. The results suggest that unique life-history traits of Japanese white sharks may be caused by genetic differences.
In some respects, these sharks behave more like whales and dolphins than other fish.
Animal movements and the acquisition and allocation of resources provide mechanisms for individual behavioural traits to propagate through population, community and ecosystem levels of biological organization. Recent developments in analytical geochemistry have provided ecologists with new opportunities to examine movements and trophic dynamics and their subsequent influence on the structure and functioning of animal communities. We refer to this approach as ecogeochemistry—the application of geochemical techniques to fundamental questions in population and community ecology. We used meta-
analyses of published data to construct δ2H, δ13C, δ15N, δ18O and Δ14C isoscapes throughout the world’s oceans. These maps reveal substantial spatial variability stable isotope values on regional and ocean-
basin scales. We summarize distributions of dissolved metals commonly assayed in the calcified tissues of marine animals. Finally, we review stable isotope analysis (SIA ) of amino acids and fatty acids. These analyses overcome many of the problems that prevent bulk SIA from providing sufficient geographic or trophic resolution in marine applications. We expect that ecologists will increasingly use ecogeochemistry approaches to estimate animal movements and trace nutrient pathways in ocean food webs. These studies will, in turn, help provide the scientific underpinning for ecosystem-based management strategies in marine environments.
Commercial longline fisheries were monitored for white sharks throughout the year, but this species was captured only from January to April. All were captured in continental shelf waters from 37 to 222 km off the west coast of Florida when sea surface temperatures ranged from 18.7° to 21.6°C. Depths at capture locations ranged from 20 to 164 m. -from Authors
Pop-up satellite archival tags (PSATs) were used to study the migration patterns and habitat preference of 56 white sharks tagged off Guadalupe Island, Mexico, between 2000 and 2008. Nine tags were recovered, providing 1021 d of high resolution (2 min) archival data. Two individual sharks were tagged in consecutive years, providing 2 yr of tracking data for each individual. White sharks were found to make long-range, seasonal migrations from Guadalupe Island to an offshore pelagic habitat, sometimes traveling as far west as the Hawaiian Islands. The pelagic region inhabited by Guadalupe Island white sharks corresponds with that reported for sharks tagged off central California; thus we have termed it the Shared Offshore Foraging Area (SOFA). Sharks spent at least 5 mo off Guadalupe Island before beginning their migration around 15 February on average (earliest 21 December, latest 5 May). They traveled through a migration corridor in an average time of 16 d at an average speed of 3.2 km h(-1) and remained in the SOFA for an average duration of 140 d. Males and females began their offshore migrations around the same time and traveled to the same area, but males were found to return to Guadalupe Island on average around 22 July (earliest 15 July, latest 30 July), while females remained in the SOFA into early autumn. Diving profiles of sharks in the SOFA strongly suggest feeding behavior; however, the targeted prey species are unknown at this time.
Understanding of juvenile life stages of large pelagic predators such as the white shark Carcharodon carcharias remains limited. We tracked 6 juvenile white sharks (147 to 250 cm total length) in the eastern Pacific using pop-up satellite archival tags for a total of 534 d, demonstrating that the nursery region of white sharks includes waters of southern California, USA, and Baja California, Mexico. Young-of-the-year sharks remained south of Point Conception whereas one 3 yr old shark moved north to Point Reyes. All juvenile white sharks displayed a diel change in behavior, with deeper mean positions during dawn, day and dusk (26 +/- 15 m) than during night (6 +/- 3 m). Sharks occasionally displayed deeper nocturnal movements during full moon nights. On average, vertical excursions were deeper and cooler for 3 yr olds (226 +/- 81 m; 9.2 +/- 0.9 degrees C) than young-of-the-year animals (100 +/- 59 m; 11.2 +/- 1.4 degrees C). Juvenile white sharks are captured as bycatch in both US and Mexican waters, suggesting that management of fishing mortality should be of increased concern.
Basic population parameters and behaviours of great white sharks, Carcharodon carcharias, were studied during four expeditions to Spencer Gulf, South Australia. In all, 58 white sharks were observed, ranging in length from about 2.2 to 5.5 m TL (X= 3.7 m TL ± 0.7 s.d.); of these sharks, 32 were subsequently tagged. Many sharks were observed repeatedly, the most frequently resighted individual being seen on 22 days over a 197-day period spanning two expeditions. Sharks in the study area were segregated by sex but not by size. Females were most abundant at 'inshore' islands, whereas males occurred mainly at 'offshore' islands. Further, there were no marked differences in abundance between summer and winter.
Nine ultrasonic trackings, lasting a maximum of 27.5 h, revealed three general horizontal movement patterns: downstream circling, island patrolling, and inter-island cruising. Average rate of movement was 3.2 km h⁻¹ (n = 145 time intervals of 15 min each). Sharks generally remained near the surface or along the bottom (about 20 m), spending relatively little time in midwater. Daytime swimming depths were significantly shallower than those at night.
Ages of white sharks, Carcharodon carcharias, from the east coast of South Africa were estimated by counting growth rings (GRs) in vertebral centra and relating them to length and mass. The vertebrae of 61 females (128-297 cm precaudal length (PCL)) and 53 males (142-373 cm PCL) were examined. Mass range was 42-442 kg for females (n=60) and 46-882 kg for males (n=53). X-radiography was used to enhance the visibility of the GRs in whole centra. Counts were made directly from the x-radiographs by one reader and from scanned x-radiographs by two readers. Count precision for each method and reader was determined by using the average percentage error (APE) index which ranged from 5.3 to 6.1%. One shark injected with oxytetracycline (OTC) was recaptured after 942 days at liberty. The shark was tagged at 140 cm and 46 kg and grew 69 cm and 104 kg. The OTC was visible in the vertebra and there was evidence of annual growth ring deposition. This could, however, not be confirmed with centrum analyses of the entire sample. The number of GRs counted varied in the following manner. The female and male with the lowest number of GRs, had 0 GR (131 cm PCL) and 1 GR (142 cm PCL), respectively. The female and male with the highest number of GRs, had 8 GRs (282 cm PCL) and 13 GRs (373 cm PCL), respectively. The smallest mature male had 8 GRs (293 cm PCL); there were no mature females. Von Bertalanffy parameters for the combined sexes were L(∞)=544 cm PCL, k=0.065/yr, t0=-4.4 yr. Growth calculated from predicted lengths decreased from 26 cm for sharks with 1 GR to 12 cm for sharks with 13 GRs, Gompertz parameters were w0=54 kg, G=3.94, g=0.094/yr. Growth calculated from predicted mass increased from 23 kg (1 GR) to 94 kg (13 GRs). Back-calculated lengths and mass were lower than observed values and Lee's phenomenon was evident in both back-calculated lengths and mass but not consistently.
We tracked 10 leatherback turtles by satellite from 2 Florida Atlantic Coast nesting beaches for a period ranging from 38 days to more than 454 days. Movement and foraging areas were often coastal, which contrasts with other satellite telemetry studies where leatherbacks are more pelagic. Using kernel home-range estimation we identified the primary internesting residence areas as well as Atlantic foraging areas. The primary internesting habitat was centered east-southeast of Cape Canaveral, Florida, from 2 to 60 km offshore and extending 215 km along the coast. Atlantic foraging areas were located primarily on the continental shelf from 30 degrees to 50 degrees N, and in an offshore area centered at 42 degrees N, 65 degrees W, as well as off Africa in the Mauritania upwelling. Seasonally, the location of these foraging areas changed, occurring on the North American continental shelf from March through November and off the shelf from December through February. One of the tracked turtles may have been killed with 17 other leatherbacks by coastal shrimp fishing located near the Georgia-Florida border. We illustrate how using remotely sensed data could be used to prevent such mortalities.
The US. Marine Mammal Protection Act requires that the abundance of marine mammals in U.S. waters be assessed. Because this requirement had not been met for a large portion of the North Atlantic Ocean (U.S. waters south of Maryland), a ship-based, line-transect survey was conducted with a 68 m research ship between Maryland (38.00degreesN) and central Florida (28.00degreesN) from the 10-m isobath to the boundary of the U.S. Exclusive Economic Zone. The study area (573,000 km(2)) was surveyed between 8 July and 17 August 1998. Minimum abundance estimates were based on 4163 km of effort and 217 sightings of at least 13 cetacean species and other taxonomic categories. The most commonly sighted species (number of groups) were bottlenose dolphins, Tursiops truncatus (38); sperm whales, Physeter macrocephalus (29); Atlantic spotted dolphins, Stenella frontalis (28); and Risso's dolphins, Grampus griseus (22). The most abundant species (abundance; coefficient of variation) were Atlantic spotted dolphins (14,438; 0.63); bottlenose dolphins (13,085; 0.40); pantropical spotted dolphins, S. attenuata (12,747; 0.56); striped dolphins, S. coeruleoalba (10,225; 0.91); and Risso's dolphins (9533; 0.50). The abundance estimate for the Clymene dolphin, S. clymene (6086; 0.93), is the first for the U.S. Atlantic Ocean. Sperm whales were the most abundant large whale (1181; 0.51). Abundances for other species or taxonomic categories ranged from 20 to 5109. There were an estimated 77,139 (0.23) cetaceans in the study area. Bottlenose dolphins and Atlantic spotted dolphins were encountered primarily in continental shelf (<200 m) and continental slope waters (200-2000 m). All other species were generally sighted in oceanic waters (>200 m). The distribution of some species varied north to south. Striped dolphins, Clymene dolphins, and sperm whales were sighted primarily in the northern part of the study area; whereas pantropical spotted dolphins were sighted primarily in the southern portion.
Based on 239 observations of 22 known-individual white sharks from 1987 to 2000, we report a temporal, sex-specific occurrence pattern among adult white sharks at the South Farallon Islands (SFI), California: individual males may occur every year, whereas individual females show a biennial occurrence pattern, being recorded every other year at most. This sex-specific occurrence pattern implies a 2-year reproductive cycle, resulting in a lower reproductive potential than previously thought, which has important implications for the conservation of this species. These results also suggest that female white sharks may travel significant distances in the North Pacific Ocean during a biennial reproductive cycle to give birth, whereas copulation may occur closer to northern California, allowing males to return annually to SFI.
Describes the bathymetry, hydrography, primary productivity, nutrients, zooplankton, benthos, fish fauna, and fish biomass and yield. Discussion centres on production in different trophic levels of NW Atlantic shelf ecosystems, and on possible explanations for production differences. Use of the shelf as a source of petrogenic hydrocarbons and for waste disposal has heightened concern over the health of these waters. Over 1968-75, total fin fish biomass of the shelf was reduced by several million metric tons of mid-sized predators, representing >50% of the fish biomass, and resulting in perturbation of the structure of the ecosystem. During the later 1970s demersal stocks showed signs of recovery, but herring Clupea harengus and mackerel Scomber scombrus biomass remained low. Since 1980, mackerel biomass has increased significantly. -P.J.Jarvis
Aim
To determine the genetic structure of the white shark population around the South African coastline and, by including data from animals sampled elsewhere in the world, to provide new insights into white shark evolution at the global scale.
Methods
Mitochondrial and microsatellite analyses were performed on 302 free‐ranging white sharks collected from five sites along the South African coastline. This was augmented with 58 GenBank sequences originating from five distinct global populations. Genetic diversity, local population sub‐structuring analyses and global phylogeographical patterns were determined.
Results
Four mt DNA haplotypes restricted to South Africa were recovered. One common haplotype was shared by 89% of all the individuals and was 13 bp different from the second most common haplotype shared by 10% of the remaining sharks. No local geographical sub‐structuring was evident for either mt DNA or nuclear DNA . Both data sets show a remarkably low level of genetic diversity (mt DNA : h = 0.205, π = 0.0027; nDNA : N a = 7.6, H o = 0.675). At the global scale, three distinct geographical clades were detected which could not be connected with 95% confidence in the haplotype network.
Main conclusions
Results indicate that the observed South African mt DNA biogeographical pattern and diversity levels may be a consequence of a severe bottleneck or a recent colonization event from one or two sources. Globally, the population of white sharks can be differentiated into three mt DNA clades confined to (1) the Mediterranean and Indo‐Pacific Oceans (Australia and California), (2) the North West Atlantic (Florida) and Indian Ocean (South Africa), and (3) a single divergent haplotype restricted to South Africa. The pattern is most likely the result of a combination of site philopatry, isolation by distance, infrequent long‐distance dispersal, isolated founder events and the closure of the Isthmus of Panama.
To date, movement patterns of juvenile sand tigers (Carcharias taurus) along the east coast of the USA have been loosely defined. Given the magnitude of the purported decline in the sand tiger population in the western North Atlantic (WNA), characterization of the species' movement patterns throughout this broad area is essential for the effective management and recovery of this population. Using passive acoustic telemetry, pop-up satellite archival transmitting tags, and conventional fishery-dependent tag/recapture data, seasonal movements of juvenile sand tigers (ages 0-2 years; < 125 cm fork length) were monitored between Maine and Florida along the US east coast from 2007 to 2013. Collectively, tag data indicated that juvenile sand tigers undergo extensive seasonal coastal migrations moving between summer (June-October) habitat (Maine to Delaware Bay) and winter (December-April) habitat (Cape Hatteras to central Florida) during the spring (April-June) and fall/early winter (October-December). Juvenile sand tigers occurred in a wide range of temperatures (9.8-26.9 A degrees C) throughout the year, but spent the majority of their time in water from 12 to 20 A degrees C. Given the extensive movements and continuous utilization of relatively shallow (< 80 m) nearshore waters exhibited by these relatively small individuals throughout their first years of life, it is imperative that precautions be taken to limit negative effects of anthropogenic interactions on this species (i.e., fisheries bycatch, coastal degradation) in an effort to rebuild and sustain the WNA population.
Georges Bank, a shallow submarine plateau located off the New England coast, has supported valuable commercial fisheries for several centuries. The region is characterized by high levels of primary productivity and, historically, high levels of fish production, Within the last four decades Georges Bank has been subjected to major perturbations that have profoundly altered levels of catch, abundance, and species composition. The arrival of distant water Beets during the early 1960s resulted in dramatic increases in effective fishing effort and the subsequent commercial collapse of several fish populations. Total fish biomass is estimated to have declined by >50% on Georges Bank during the period of operation of the distant water Beets, The implementation of extended jurisdiction (the 200-mile [370.4-km] limit) in 1977 was followed by modernization and increased capacity of the domestic Beet, resulting in a second perturbation to the system that resulted in further declines in groundfish populations to historically low levels, A subsequent increase in the abundance of species of low commercial value was documented, with an apparent replacement of gadid and Bounder species by small elasmobranchs (including dogfish sharks and skates), Examination of feeding guild structure suggests that this switch in species dominance may have been Linked to a competitive release, The small elasmobranchs, notably dogfish sharks, also prey on species of commercial importance (primarily small pelagics, including herring and mackerel), The cumulative impacts on the groundfish populations as a result of intense exploitation and predation pressure may have been further exacerbated by effects of fishing gear on the physical structure of the habitat. Implications for the development of an ecosystem-based management approach are described.
Sexual segregation occurs when members of a species separate such that the sexes live apart, either singly or in single‐sex groups. It can be broadly categorised into two types: habitat segregation and social segregation. Sexual segregation is a behavioural phenomenon that is widespread in the animal kingdom yet the underlying causes remain poorly understood. Sexual segregation has been widely studied among terrestrial mammals such as ungulates, but it has been less well documented in the marine environment. This chapter clarifies terms and concepts which have emerged from the investigation of sexual segregation in terrestrial ecology and examines how a similar methodological approach may be complicated by differences of marine species. Here we discuss the behavioural patterns of sexual segregation among marine fish, reptile, bird and mammal species. Five hypotheses have been forwarded to account for sexual segregation, largely emerging from investigation of sexual segregation in terrestrial ungulates: the predation risk, forage selection, activity budget, thermal niche–fecundity and social factors hypotheses. These mechanisms are reviewed following careful assessment of their applicability to marine vertebrate species and case studies of marine vertebrates which support each mechanism recounted. Rigorous testing of all hypotheses is lacking from both the terrestrial and marine vertebrate literature and those analyses which have been attempted are often confounded by factors such as sexual body‐size dimorphism. In this context, we indicate the value of studying model species which are monomorphic with respect to body size and discuss possible underlying causes for sexual segregation in this species. We also discuss why it is important to understand sexual segregation, for example, by illustrating how differential exploitation of the sexes by humans can lead to population decline.
The movements and behavior of 22 juvenile White Sharks, Carcharodon carcharias [1.75–2.6 m total length (TL)], were monitored in eastern Australia using satellite tracking and pop-up archival tags, providing a total of 1,941 d of data. Broad-scale movements were primarily coastal, were highly directional with high angular concentration values r (mean r = 0.81; SD = 0.16), and ranged over 2,000 km of the Australian coastline from eastern Tasmania to southern Queensland. One 2.1-m male also traveled 3,600 km across the Tasman Sea to New Zealand, through Cook Strait, and east onto the Chatham Rise. Directional movement was interspersed with periods of temporary residency denoted by significantly lower r values (mean r = 0.22; SD = 0.17) and a highly restricted geographic footprint. Residency sites were limited in number, and season of occupancy suggesting that juvenile White Sharks have a relatively small number of interconnected preferred habitat areas in eastern Australia. The consistent occupancy of two residency sites over multiple years, the Corner Inlet- Ninety Mile Beach region off eastern Victoria and the Port Stephens region of New South Wales, defined these as seasonal nursery areas. On-shelf shark activity was primarily shoreward of the 120-m depth contour in nursery areas. Sharks moving between nursery areas showed a propensity to travel over a corridor spanning bottom depths of 60–120 m, with 55% of all ARGOS positions located over this zone. This depth zone includes relic coastline structures in eastern Australia, which may offer cues for navigation or enhanced foraging opportunities by providing focal areas for prey species. However, sharks also made occasional dives to 300–500 m when traveling and when off-shore. The maximum depth recorded by a 1.9-m female was 984 m. Sharks showed considerable plasticity in swimming behavior, recording most patterns previously identied in juvenile, subadult, and adult stages of this species. The similarity in the dominant temperature range experienced by juvenile White Sharks between our data and other studies suggests a propensity to occupy waters of 18–20ºC. Nursery areas in eastern Australia are coincident in time and space with aggregations of various fin fish species that provide suitable prey and coincided with areas of seasonal upwelling and subsequent nutrient enrichment. The smaller sizes of juveniles recorded from the Corner Inlet region of eastern Victoria suggests that pups may initially recruit to this nursery area prior to establishing a seasonal migratory pathway along the east coast to the Port Stephens nursery area of central New South Wales. The potential exists for juvenile White Sharks to be taken as bycatch in nearshore, shelf, and slope fishing activities in the vicinity of these nursery areas. Forays seaward of the shelf break, offshore diving behavior, and open-ocean travel may also expose juvenile White Sharks to incidental capture in offshore pelagic fisheries previously considered not to pose such a threat.
Juvenile White Sharks (JWS) in Australian waters appear to occupy different coastal habitats during their early years. Two juvenile nursery areas are known in southeastern Australia, each with different resident periods. Juveniles are seasonally resident in the Port Stephens region of central New South Wales from mid-August to early January. Sharks commonly occur at the second known nursery area in coastal waters of eastern Bass Strait, 900 km south, from January to April. Movements between the two nursery areas occur in the nonresident periods. At the Port Stephens site, sharks are highly visible in the nearshore surf zone where interactions with recreational fishers and beach users are frequently reported. To examine potential interactions in these coastal zones, habitat use within and between the nursery areas is being studied with a range of electronic tags. Twenty-five JWS have been tagged in the Port Stephens region, seven of these with a pop-up archival transmitting (PAT) tag. Because six of the PAT tags were washed ashore and returned, the full archive data set was recovered. We used a novel mean first difference analysis, guided by supplemental location data from satellite and acoustic tags where available, to define behavioral modes and provide an indication of habitat use when sharks were resident at and when traveling between the Port Stephens and the Bass Strait nursery areas. These analyses identified a suite of behaviors for sharks ranging from shallow-water bottom-orientated swimming behavior consistent with surf-zone habitat use, diel behavior in deeper waters, continental slope (400–600 m), and open- ocean excursions with dives to nearly 1000 m. The transition phase between residency and traveling periods was characterized by multiple behavior modes indicative of short forays between the surf zone and shelf edge. Classification of the behavioral modes allows estimates of time when human interactions may occur, even without fine-scale position data.