Bradley M. Wetherbee currently works at the Department of Biological Sciences, University of Rhode Island. Bradley does research in Marine Biology and Ecology. Their current project is 'Movements of pelagic sharks.'
Skills and Expertise
Research Items (82)
Transboundary marine species have an increased risk of overexploitation as management regimes and enforcement can vary among states. The complex geopolitical layout of exclusive economic zones (EEZs) in the Western Indian Ocean (WIO) introduces the potential for migratory species to cross multiple boundaries, consequently a lack of scientific data could complicate regional management. In the current study, we highlight both the relative lack of spatial data available in the WIO, and the prevalence of transboundary movements in species that have previously been studied in the region. Five tiger sharks Galeocerdo cuvier were tracked with near real‐time positioning (SPOT) satellite tags to determine individual shark movements relative to EEZs within the WIO. Concurrently, a literature search was performed to identify all satellite telemetry studies conducted to date in the WIO for marine megafaunal species, and the results compared to global satellite telemetry effort. Finally, the satellite tracks of all marine species monitored in the WIO were extracted and digitized to examine the scale of transboundary movements that occur in the region. Tiger sharks exhibited both coastal and oceanic movements, with one individual crossing a total of eight EEZs. Satellite telemetry effort in the WIO has not matched the global increase, with only 4.7% of global studies occurring in the region. Species in the WIO remained within the EEZ in which they were tagged in only three studies, while all other species demonstrated some level of transboundary movement. This study demonstrates the lack of spatial data available for informed regional management in an area where transboundary movements by marine megafauna are highly prevalent. Without more dedicated funding and research, the rich biodiversity of the WIO is at risk of overexploitation from the diverse threats present within the various political regions.
Pelagic sharks are vulnerable to overfishing because of their low reproductive rates, generally low growth rates, and high catch rates in tuna and billfish fisheries worldwide. Pelagic sharks often migrate long distances, but they may also occur close to shore, making it difficult to classify their behaviour on the continuum from oceanic nomad to coastal resident. This has important implications for fishery management, which must be targeted at an appropriate spatial scale. Conventional tagging indicates that shortfin mako sharks move widely around the southwest Pacific Ocean, but there is little information on their habitat use or mobility in the region. This study deployed electronic tags on 14 mostly juvenile New Zealand mako sharks to investigate their habitat use, and the spatial and temporal scale of their movements. Movement behaviour was classified as Resident or Travel, with the former focused in New Zealand coastal waters, and the latter in oceanic waters around New Zealand and along oceanic ridges running north towards the tropical islands of Fiji, Vanuatu and New Caledonia. Sharks regularly switched between Resident and Travel behavioural states, but their residency periods sometimes lasted for several months. Sharks spent most of their time in the New Zealand Exclusive Economic Zone (median 77%, five sharks > 90%), presumably because of the high coastal productivity and access to abundant prey. These results challenge the conventional view that mako sharks are nomadic wanderers, and suggest that fishing mortality should be managed at a local as well as a regional scale.
Spatial ecology of Carcharias taurus in the northwestern Mid-Atlantic coastal ocean D. E. Haulsee*, M. W. Breece, L. M. Brown, B. M. Wetherbee, D. A. Fox, M. J. Oliver *Email: email@example.com ABSTRACT: Sand Tiger sharks Carcharias taurus are a highly migratory coastal species with declining populations worldwide. This species exhibits many behaviors that make coastal sharks difficult to manage, including aggregatory behavior, sexual segregation, and large-scale migrations through shallow coastal waters with many opportunities for human interactions. Sand Tigers from the Western North Atlantic subpopulation are known to seasonally inhabit Delaware Bay and surrounding coastal waters. This region has been recommended as a Habitat Area of Particular Concern for the Western North Atlantic Sand Tiger population and increased understanding of their movements and habitat requirements will facilitate management efforts. We developed models to predict Sand Tiger occupancy using spatially dynamic environmental predictors. Our models predicted Sand Tiger (all sharks combined, adult males, adult females, and juveniles) occurrences in two study regions, the Delaware Bay, and the western Mid-Atlantic coastal ocean. Sea surface temperature, day of year, water depth, and remote sensing reflectance at 555 nm were the most important environmental predictors of occurrence, and correctly predicted 80-89% of Sand Tiger acoustic telemetry records in the two study regions. Our models predicted differences in the timing and location of occurrences among juvenile and adult Sand Tigers, as well as areas where these life history stages overlap in the Mid-Atlantic coastal ocean. Our hope is that a daily forecast of Sand Tiger occurrence from our modeling efforts, could be useful for conservation and management efforts in this important region, as well as for studying the spatial and behavioral ecology of this important top-predator.
Concurrently, assessing the effectiveness of marine protected areas and evaluating the degree of risk from humans to key species provide valuable information that can be integrated into conservation management planning. Tiger sharks (Galeocerdo cuvier) are a wide‐ranging ecologically important species subject to various threats. The aim of this study was to identify “hotspots” of tiger shark habitat use in relation to protected areas and potential risks from fishing. Southwest Indian Ocean, east coast of South Africa and Mozambique. Satellite tags were fitted to 26 tiger sharks. A subset of 19 sharks with an average period at liberty of 197 (SD = 110) days were analysed using hotspot analysis to identify areas of core habitat use. The spatial and temporal overlap of significant hotspots with current and planned marine protected areas as well as risks from fishing and culling was then calculated. There was a 5.97% spatial overlap between tiger shark hotspots and marine protected areas, which would increase significantly (p < .05) to 24.36% with the expansion of planned protected areas in South Africa and could be as high as 41.43% if Mozambique similarly expanded neighbouring protected area boundaries. Tiger sharks remained largely coastal, but only showed a spatial overlap of 5.12% with shark culling nets in South Africa. Only three sharks undertook open ocean migrations during which they were more likely to interact with longline fisheries in the region. This study demonstrates how spatial information can be used to assess the overlap between marine protected areas and the core habitats of top marine predators and highlights how congruent transnational conservation management can improve the effectiveness of protected areas. Core habitat use of marine apex predators may also be indicative of productive habitats, and therefore, predators such as tiger sharks could act as surrogate species for identifying key habitats to prioritize for conservation planning.
Grouper spawning aggregations along deep reefs of the US Virgin Islands represent a large potential prey source for predators including sharks. To examine the relationship between grouper spawning aggregations and sharks, we tagged three species of groupers and three species of sharks with acoustic transmitters and monitored their movements over several years using an array of receivers deployed at spawning sites and at non-spawning locations along the southern shelf edge of St. Thomas, US Virgin Islands. Each species of shark demonstrated different behavioral patterns. Temporal and spatial patterns of movement of lemon sharks (Negaprion brevirostris) were closely associated with spawning events, but little connection between spawning aggregations and behavior of the other two species of sharks (Carcharhinus perezi , Galeocerdo cuvier). Our findings illustrate variable interactions that may occur between different species of sharks and grouper spawning aggregations and that prey availability may influence the spatial and temporal patterns of activity of co-occurring species of sharks in different ways.
Project - Hawaii Sharks
Vertical distribution, diet, and reproduction of the velvet dogfish (Zameus squamulosus) in waters off Hawaii
The velvet dogfish (Zame-us squamulosus) is a wide-ranging species of shark that is captured as bycatch in bottom and pelagic long-line fisheries in the Atlantic, Pacific, and Indian oceans from near the surface to depths as great as 2000 m. Here we provide information on the vertical distribution, diet, and reproduction of the velvet dogfish based on examination of 21 specimens captured in Hawaiian longline fisheries. Only females (576-839 mm in total length [TL]) were captured in waters off Hawaii and this finding may indicate sexual segregation for this species. All individuals were captured in epipelagic and pelagic oceanic waters at estimated target hook depths between 24 and 400 m. Stomach and intestinal contents consisted of squid, fish, and shrimp. Females were immature at 576-729 mm TL and mature at 715-839 mm TL. Mature females contained 6-10 uterine eggs and 4-8 embryos. On the basis of results from a pregnant female (715 mm TL), the size of ovarian ova, and the width of the uteri of slightly larger individuals, female maturity was estimated to occur at 715-730 mm TL. No reproductive seasonality was detected; however, our sample size was small. Reproductive data from published records for size of near-term embryos and smallest free-swimming specimens with umbilical scars indicate that size at birth is 245-270 mm TL.
The extent of increasing anthropogenic impacts on large marine vertebrates partly depends on the animals' movement patterns. Effective conservation requires identification of the key drivers of movement including intrinsic properties and extrinsic constraints associated with the dynamic nature of the environments the animals inhabit. However, the relative importance of intrinsic versus extrinsic factors remains elusive. We analyze a global dataset of ∼2.8 million locations from >2,600 tracked individuals across 50 marine vertebrates evolutionarily separated by millions of years and using different locomotion modes (fly, swim, walk/paddle). Strikingly, movement patterns show a remarkable convergence, being strongly conserved across species and independent of body length and mass, despite these traits ranging over 10 orders of magnitude among the species studied. This represents a fundamental difference between marine and terrestrial vertebrates not previously identified, likely linked to the reduced costs of locomotion in water. Movement patterns were primarily explained by the interaction between species-specific traits and the habitat(s) they move through, resulting in complex movement patterns when moving close to coasts compared with more predictable patterns when moving in open oceans. This distinct difference may be associated with greater complexity within coastal microhabitats, highlighting a critical role of preferred habitat in shaping marine vertebrate global movements. Efforts to develop understanding of the characteristics of vertebrate movement should consider the habitat(s) through which they move to identify how movement patterns will alter with forecasted severe ocean changes, such as reduced Arctic sea ice cover, sea level rise, and declining oxygen content.
The ability to predict animal movement based on environmental change is essential for understanding the dynamic nature of their spatial ecology, and in turn the effectiveness of conservation strategies. We used a large marine predator that displays partial migration (the tiger shark Galeocerdo cuvier) as a model to test the role of oceanic conditions in predicting the space-use of different size classes. By using generalized additive mixed models (GAMMs), we revealed that environmental variables (sea surface temperature, primary productivity, thermal fronts, and bathymetry) had much greater predictive power for the movements of large, migratory tiger sharks than for small, resident individuals. We also found that coverage of tiger shark movements within “shark sanctuaries” (protected areas specifically for sharks) in the northwest Atlantic could be increased from 12 to 52% through inclusion of Bermuda’s waters. However, as large tiger sharks are migratory, over 80% of potential longline fisheries interactions would still occur outside the boundaries of even the expanded protected areas. This emphasises that management of highly migratory species needs to be dynamic and account for changing interactions with fisheries over time, which in a changing climate may rely on predicting movements based on oceanic conditions to be effective.
- Sep 2017
The white marlin, Kajikia albida, is a highly migratory, prized sport fish of conservation concern. Improved understanding of white marlin ecology, including habitat use, will inform management measures. To improve white marlin movement knowledge in a region with limited information, we tagged 18 individuals off the eastern Yucatan Peninsula, Mexico with pop-up satellite archival transmitters. Tracks lasting 9–328 d, yielded data across 1277 d, and covered distances of 891–10 579 km. Horizontal movements varied greatly with ten individuals remaining in the Gulf of Mexico/northwestern Caribbean and eight individuals entering the western North Atlantic. Although white marlin experienced a temperature range of 10.0–33.6 C, the majority of time was spent in waters >24 C. Marlin displayed diel diving patterns with deeper dives occurring more frequently during the daytime. As water columns warmed, dive duration, maximum daily depth, and dive depth all increased. As a result, 18% of the time was spent at depths >100 m in the warmest water columns compared with <1% in the coldest water columns. Although the thermal characteristics of the water column greatly influence white marlin diving behaviour, the generally shallow distributions provide a way of separating white marlin from important fishery species.
Overfishing is a primary cause of population declines for many shark species of conservation concern. However, means of obtaining information on fishery interactions and mortality, necessary for the development of successful conservation strategies, are often fisheries-dependent and of questionable quality for many species of commercially exploited pelagic sharks. We used satellite telemetry as a fisheries-independent tool to document fisheries interactions, and quantify fishing mortality of the highly migratory shortfin mako shark (Isurus oxyrinchus) in the western North Atlantic Ocean. Forty satellite-tagged shortfin mako sharks tracked over 3 years entered the Exclusive Economic Zones of 19 countries and were harvested in fisheries of five countries, with 30% of tagged sharks harvested. Our tagging-derived estimates of instantaneous fishing mortality rates (F = 0.19–0.56) were 10-fold higher than previous estimates from fisheries dependent data (approx. 0.015–0.024), suggesting data used in stock assessments may considerably underestimate fishing mortality. Additionally, our estimates of F were greater than those associated with maximum sustainable yield, suggesting a state of overfishing. This information has direct application to evaluations of stock status and for effective management of populations, and thus satellite tagging studies have potential to provide more accurate estimates of fishing mortality and survival than traditional fisheries-dependent methodology.
Background Blue sharks (Prionace glauca) are among the most abundant and widely distributed of oceanic elasmobranchs. Millions are taken annually in pelagic longline fisheries and comprise the highest component of auctioned fin weight in the international shark fin trade. Though studies of blue sharks outnumber those of other large pelagic sharks, the species’ complicated and sexually segregated life history still confound current understanding of Atlantic movement patterns. Lack of detailed information regarding movement and vertical behavior continues to limit management efforts that require such data for stock assessment and sustainable catch modeling. Therefore, this study aims to describe behavioral and ecological patterns distinct to aggregating and migrating blue sharks, and compare the findings to existing Atlantic movement models. Results Data collected from 23 blue sharks instrumented with pop-up satellite archival tags were used in statistical predictive regression models to investigate habitat use during a localized aggregation in the northwest Atlantic, while undergoing seasonal migrations, and with respect to environmental variables. Deployment durations ranged from 4 to 273 days, with sharks inhabiting both productive coastal waters and the open ocean, and exhibiting long-distance seasonal movements exceeding 3700 km. While aggregating on the continental shelf of the northwest Atlantic, blue sharks displayed consistent depth use independent of sex and life stage, and exhibited varied response to environmental (temperature and chlorophyll a) factors. As sharks dispersed from the aggregation site, depth use was influenced by bathymetry, latitude, demography, and presence in the Gulf Stream. Mature females were not observed at the New England tagging site, however, two mature females with recent mating wounds were captured and tagged opportunistically in The Bahamas, one of which migrated to the Mid-Atlantic Ridge. Conclusions Vertical behaviors displayed by blue sharks varied greatly among locales; depth use off the continental shelf was significantly greater, and individuals exhibited a greater frequency of deep-diving behavior, compared to periods of aggregation on the continental shelf. Sexual segregation was evident, suggesting mature and immature males, and immature females may be subjected to high levels of anthropogenic exploitation in this region during periods of aggregation. Analysis of the spatio-temporal tracks revealed that nine individuals traveled beyond the United States EEZ, including a mature female captured in The Bahamas that migrated to the Mid-Atlantic Ridge. These results reflect and augment existing Atlantic migration models, and highlight the complex, synergistic nature of factors affecting blue shark ecology and the need for a cooperative management approach in the North Atlantic. Electronic supplementary material The online version of this article (doi:10.1186/s40462-017-0107-z) contains supplementary material, which is available to authorized users.
A new record of Megachasma pelagios is here reported for the tropical western North Atlantic Ocean from Puerto Rico. On December 10, 2016, a tourist reported an unusual stranded shark on Mojacasabe Beach, Cabo Rojo, on the southwestern coast of Puerto Rico. Visual examination of the carcass and mitochondrial DNA analysis from a dorsal fin sample revealed it to be a 457 cm female megamouth shark. This record represents the first record of M. pelagios for the tropical western North Atlantic Ocean within the Caribbean Sea of southwest Puerto Rico and only the second record of M. pelagios from the North Atlantic.
The popularity of recreational shark fishing appears to be on the rise in recent years, with current policies often failing to address the direct targeting of protected species in this sector. Examination of catch trends from the past decade revealed that more than 66 million sharks were caught by recreational anglers along the U.S. eastern coast alone, including more than 1.2 million prohibited species. Using Sand Tigers Carcharias taurus captured by volunteer anglers as a case study to evaluate post-release mortality, 33 individuals were fitted with external acoustic tags and passively tracked using an array of acoustic receivers. Although rates of internal hooking and gear retention were high (57% and 60%), short-term post-release mortality was relatively low (6%) and was heavily influenced by hook location and retention. Given the dramatic increase in the range and extent of recreational fishing targeting prohibited species, even relatively low mortality rates may still pose a significant threat to recovery.
A new species of lanternshark, Etmopterus lailae (Squaliformes: Etmopteridae), is described from the Northwestern Ha-waiian Islands, in the central North Pacific Ocean. The new species resembles other members of the " Etmopterus lucifer " clade in having linear rows of dermal denticles, and most closely resembles E. lucifer from Japan. The new species occurs along insular slopes around seamounts at depths between 314–384 m. It can be distinguished from other members of the E. lucifer clade by a combination of characteristics, including a longer anterior flank marking branch, arrangement of der-mal denticles on the ventral snout surface and body, flank and caudal markings, and meristic counts including number of spiral valve turns, and precaudal vertebrate. A key to species of the Etmopterus lucifer-clade is included.
Southern stingrays (Hypanus americanus) represent a multimillion dollar ecotourism operation in Grand Cayman, interacting with over a million visitors annually. Over 30 years of stingray provisioning by tour operators has provided a predictable aggregation at the Stingray City Sandbar (SCS). Despite potentially negative effects of provisioning and concerns about declining stingray numbers at SCS, there has never been a formal assessment of the aggregation. In the present study we analysed tagging data from 2002 to 2015 and established structured censuses monitoring the aggregation. The consistently female-dominated aggregation declined between 2008 and 2012, from >100 to <60 stingrays, but has increased since 2012, stabilising at ~90 stingrays. Female site fidelity was high, with ~20% of females resident for ≥10 years, compared with only 3 years for most males. Stingrays were also found to have growth rates similar to those in captivity. The results of the present study suggest the SCS aggregation is highly dependent on individuals arriving from the island-wide stingray population, susceptible to perturbation, and that successful management of activities at SCS will benefit from regular monitoring of the stingray aggregation. We chronicle the historical status of this well-known and economically valuable marine resource and provide suggestions applicable towards sustainable human–marine wildlife interactions for similar resources.
- Dec 2016
As upper level predators, sharks serve an important role in marine ecosystems, but are often at risk from fisheries. Successful management of these species will require detailed information about their movements and distributions. 2.Using satellite telemetry, we investigated the long-term horizontal movements and seasonal distributions of shortfin mako sharks Isurus oxyrinchus in the western North Atlantic Ocean. 3.Twenty-six sharks (14 USA, 12 Mexico) were tracked for durations of 78–527 days. Ten sharks were tracked for >1 year. Sharks displayed region-specific movements, with little distributional overlap between the Gulf of Mexico and Caribbean Sea, and the western North Atlantic. Sharks tagged off the USA ranged over a larger area, including shelf and pelagic habitats. Their core distribution was largely over the continental shelf and fluctuated seasonally, ranging from South Carolina, USA, in the winter to Nova Scotia, Canada, in the autumn, and appeared to follow seasonal productivity peaks while favouring warmer waters. Sharks tagged off Mexico displayed more restricted movements, largely confined to shelf habitats, with core activity centred year-round on the eastern Campeche Bank, Mexico. 4.Sharks moved across the jurisdictional management boundaries of 17 nations, and the proportion of tracked sharks harvested (22%) was twice that obtained from previous fisheries-dependent, conventional tagging studies. 5.Sharks also displayed considerable variability in movements, with seven sharks tagged off the USA making long-distance, highly directional southern excursions into unproductive subtropical/tropical waters before returning north. 6.Policy implications. The large-scale and region-specific movements of shortfin mako sharks underscore the need for close cooperation amongst western North Atlantic nations and implementation of regionally- and seasonally-specific management strategies. The movement patterns also provide baseline information, which could be used in spatially explicit stock assessment models. Identification of high-use areas by shortfin mako sharks provides focal areas for quantifying interactions with fisheries. The high harvest rate observed in our fisheries-independent tracking study raises questions about the true rate of fisheries mortality experienced by shortfin mako sharks, calling for a cautionary interpretation of past stock assessments used to determine management policy for this highly migratory species of conservation concern. This article is protected by copyright. All rights reserved.
Knowledge of genetic connectivity dynamics in the world's large-bodied, highly migratory, apex predator sharks across their global ranges is limited. One such species, the tiger shark (Galeocerdo cuvier), occurs worldwide in warm-temperate and tropical waters, uses remarkably diverse habitats (nearshore to pelagic), and possesses a generalist diet that can structure marine ecosystems through top down processes. We investigated the phylogeography and global population structure of this exploited, phylogenetically enigmatic shark by using 10 nuclear microsatellites (n = 380) and sequences from the mitochondrial control region (CR, n = 340) and cytochrome oxidase I gene (n = 100). All three marker classes showed genetic differentiation between tiger sharks from the western Atlantic and Indo-Pacific ocean basins (microsatellite FST > 0.129; CR ?ST > 0.497), the presence of North vs. South western Atlantic differentiation, and isolation of tiger sharks sampled from Hawaii from other surveyed locations. Furthermore, mitochondrial DNA revealed high levels of intra ocean-basin matrilineal population structure, suggesting female philopatry and sex-biased gene flow. Coalescent- and genetic distance-based estimates of divergence from CR sequences were largely congruent (dcorr = 0.0015-0.0050), indicating a separation of Indo-Pacific and western Atlantic tiger sharks < 1 million years ago. Mitochondrial haplotype relationships suggested the western South Atlantic Ocean was likely a historical connection for inter-ocean basin linkages via dispersal around South Africa. Together, the results reveal unexpectedly high levels of population structure in a highly migratory, behaviorally generalist, cosmopolitan ocean predator, calling for management and conservation on smaller than anticipated spatial scales. This article is protected by copyright. All rights reserved.
Understanding of species interactions within mesophotic coral ecosystems (MCEs; ~ 30–150 m) lags well behind that for shallow coral reefs. MCEs are often sites of fish spawning aggregations (FSAs) for a variety of species, including many groupers. Such reproductive fish aggregations represent temporal concentrations of potential prey that may be drivers of habitat use by predatory species, including sharks. We investigated movements of three species of sharks within a MCE and in relation to FSAs located on the shelf edge south of St. Thomas, United States Virgin Islands. Movements of 17 tiger (Galeocerdo cuvier), seven lemon (Negaprion brevirostris), and six Caribbean reef (Carcharhinus perezi) sharks tagged with acoustic transmitters were monitored within the MCE using an array of acoustic receivers spanning an area of 1,060 km2 over a five year period. Receivers were concentrated around prominent grouper FSAs to monitor movements of sharks in relation to these temporally transient aggregations. Over 130,000 detections of telemetered sharks were recorded, with four sharks tracked in excess of 3 years. All three shark species were present within the MCE over long periods of time and detected frequently at FSAs, but patterns of MCE use and orientation towards FSAs varied both spatially and temporally among species. Lemon sharks moved over a large expanse of the MCE, but concentrated their activities around FSAs during grouper spawning and were present within the MCE significantly more during grouper spawning season. Caribbean reef sharks were present within a restricted portion of the MCE for prolonged periods of time, but were also absent for long periods. Tiger sharks were detected throughout the extent of the acoustic array, with the MCE representing only portion of their habitat use, although a high degree of individual variation was observed. Our findings indicate that although patterns of use varied, all three species of sharks repeatedly utilized the MCE and as upper trophic level predators they are likely involved in a range of interactions with other members of MCEs.
Vertical movements of shortfin mako sharks Isurus oxyrinchus in the western North Atlantic Ocean are strongly influenced by temperature Jeremy J. Vaudo*, Bradley M. Wetherbee, Anthony D. Wood, Kevin Weng, Lucy A. Howey-Jordan, Guy M. Harvey, Mahmood S. Shivji *Email: firstname.lastname@example.org ABSTRACT: Although shortfin mako sharks Isurus oxyrinchus are regularly encountered in pelagic fisheries, limited information is available on their vertical distribution and is primarily restricted to cooler areas of their distribution. We investigated the vertical movements of mako sharks across differing temperature regimes within the western North Atlantic by tagging 8 individuals with pop-up satellite archival tags off the northeastern United States and the Yucatan Peninsula, Mexico. Depth and temperature records across 587 d showed vertical movements strongly associated with ocean temperature. Temperatures <15° C created a lower depth limit to most diving behaviors, and shifts in depths used coincided with changes in the thermal properties of the vertical habitat. In the warmest water columns, sharks spent 36% of the daytime at depths >150 m compared to only 1% in the coldest water columns. The sharks showed diel diving behavior, with deeper dives occurring primarily during the daytime (maximum depth: 866 m). Overall, sharks experienced temperatures between 5.2 and 31.1°C. When the opportunity was available, sharks spent considerable time in waters ranging from 22 to 27° C, indicating underestimation of the previously reported upper limit of the mako sharks’ preferred temperature. The preference for higher temperatures does not support endothermy as an adaption for niche expansion in mako sharks. The strong influence of thermal habitat on movement behavior suggests potentially strong impacts of rising ocean temperatures on the ecology of this highly migratory top predator.
Long-distance movements of animals are an important driver of population spatial dynamics and determine the extent of overlap with area-focused human activities, such as fishing. Despite global concerns of declining shark populations, a major limitation in assessments of population trends or spatial management options is the lack of information on their long-term migratory behaviour. For a large marine predator, the tiger shark Galeocerdo cuvier, we show from individuals satellite-tracked for multiple years (up to 1101 days) that adult males undertake annually repeated, round-trip migrations of over 7,500 km in the northwest Atlantic. Notably, these migrations occurred between the highly disparate ecosystems of Caribbean coral reef regions in winter and high latitude oceanic areas in summer, with strong, repeated philopatry to specific overwintering insular habitat. Partial migration also occurred, with smaller, immature individuals displaying reduced migration propensity. Foraging may be a putative motivation for these oceanic migrations, with summer behaviour showing higher path tortuosity at the oceanic range extremes. The predictable migratory patterns and use of highly divergent ecosystems shown by male tiger sharks appear broadly similar to migrations seen in birds, reptiles and mammals, and highlight opportunities for dynamic spatial management and conservation measures of highly mobile sharks.
Quantifying habitat selection in marine organisms is challenging because it is difficult to obtain species location information with multiple corresponding habitat measurements. In the ocean, habitat conditions vary on many spatiotemporal scales, which have important consequences for habitat selection. While macroscale biotic and abiotic features influence seasonal movements (spatial scales of 100−1000 km), selectivity of conditions on mesoscales (1−100 km) reflects an animal’s response to the local environment. In this study, we examined habitat selectivity by pairing acoustic telemetry with environmental habitat parameters measured by an autonomous underwater vehicle (AUV), and demonstrate that migrating sand tiger sharks Carcharias taurus along the East Coast of the USA did not randomly use the coastal environment. Of the variables examined, we found evidence to suggest that sand tigers were selecting their habitat based on distance to shore, salinity, and colored dissolved organic matter (CDOM). Notably, temperature was not predictive of habitat use in our study. We posit that during their coastal migration, sand tigers select for specific mesoscale coastal habitats that may inform navigation or feeding behaviors. To our knowledge, this is the first empirical measure of mesoscale habitat selection by a coastal marine organism using an AUV. The applications of this method extend beyond the habitat selectivity of sand tigers, and will prove useful for future studies combining in situ observations of marine habitats and animal observations.
Globally, population declines for the sand tiger shark (Carcharias taurus) have resulted in calls for informed management of populations, including in the western North Atlantic, where they have been listed as a Species of Concern by NOAA Fisheries. However, information on movements and habitat use, critical for informed management of this sand tiger population, is limited. We investigated horizontal and vertical movements of sand tigers along the US east coast using pop-up archival satellite transmitters, supplemented by acoustic telemetry. Thirteen sand tiger sharks were tagged with satellite and acoustic transmitters in Delaware Bay in late August and early September 2008. Ten of these provided satellite data for horizontal tracks using a Kalman filter. Males left Delaware Bay in autumn and moved south along the continental shelf until reaching waters off North Carolina. Females moved east to waters near the edge of the continental slope. Average depth of males was positively correlated with shark size. All individuals spent at least 95% of their time in waters of 17–238C. Sand tiger sharks appear most susceptible to fisheries in November and December. Slight expansion of the boundaries and timing of an existing shark-directed bottom longline area closure would likely reduce by-catch of sand tiger sharks and enhance recovery of the stock.
[Extract] As many of the world's shark and ray populations continue to decline (Dulvy et al. 2014) there is a growing need for improved conservation and management. One of the key requirements enabling design of effective conservation and management actions is life history parameters (Simpfendorfer et al. 2011)as these provide basic information on the dynamics of populations (Cortes 2007). Life history parameters (e.g. age, growth and reproduction) are directly tied to the reproductive output of a species, and thus unequivocally linked to the capacity of a population to withstand exploitation and to recover from decline. Despite this importance, research on the life history of sharks and rays has declined in recent years as 'cooler' and non-lethal topics have become more commonplace. However, on-going research on life history is fundamental for positive action to address declines of shark populations and policies aimed at recovery of populations. To highlight research that has been and is being conducted on the life history of sharks and rays, we have compiled a 'Shark and ray life history' virtual issue of Marine and Freshwater Research (Table 1), which is freely available from the Journal's website for a limited time.
Sand tigers (Carcharias taurus) are large apex predators common in the coastal ocean along the Eastern US Coast. Although Delaware Bay and surrounding coastal waters are known summer hot-spots for Sand Tigers, our understanding of where this population travels throughout the year is less well known. Since 2007, we have implanted more than 300 VEMCO acoustic transmitters in Sand Tigers providing detections from Cape Canaveral, Florida to Long Island, New York by collaborators in the Atlantic Cooperative Telemetry (ACT) Network. During the summer of 2012, 20 Sand Tigers were implanted with VEMCO Mobile Transceivers (VMTs), which are capable of both transmitting and receiving coded acoustic pings. To date, two of the 20 sharks have been recaptured, and their VMTs recovered. VMTs recorded detections of 350 individuals (216 Sand Tigers), from 8 species telemetered by ACT Network researchers. This represents the species assemblages associated with Sand Tigers throughout the year. Detections of species by transceivers also created a network allowing us to piece together the locations of Sand Tigers throughout the year. This project is a unique look at the social network of an apex predator and is a useful model for studies quantifying the social structures of marine animals.
Sand Tigers (Carcharias taurus) are federally listed as a Species of Concern due to population declines and inherently low rebound potential. Essential fish habitat for Sand Tigers has been identified in several areas along the U.S. coast, however little information exists regarding their spatial and temporal usage. The relatively high abundance of Sand Tigers from June-October in the Delaware Bay and nearby coast suggests these areas are particularly important habitats. Passive acoustic telemetry was used to examine fine-scale movement patterns of 33 Sand Tigers (mean 201cm FL; range 146-246cm FL) along the Delaware coast during the summers of 2012-13. Activity space was relatively restricted, with 95% kernel utilization distributions (KUD) of 7.9-303.1km2. The majority (82%) of Sand Tigers core areas of use (50% KUD) were limited to a 12km2 section of coast (<1.5km from shore) between the mouth of the Delaware Bay and Cape Henlopen, Delaware. Furthermore, 67% of individuals tagged in 2012 returned to the same nearshore waters in 2013. The high degree of site attachment to this small coastal area coupled with threats from coastal development and shore fishing targeting Sand Tigers warrants this region’s designation as a habitat area of particular concern.
Tiger sharks (Galeocerdo cuvier) are a wide ranging, potentially keystone predator species that display a variety of horizontal movement patterns, making use of coastal and pelagic waters. Far less, however, is known about their vertical movements and use of the water column. We used pop-up satellite archival tags with two data sampling rates (high rate and standard rate tags) to investigate the vertical habitat use and diving behavior of tiger sharks tagged on the Puerto Rico–Virgin Islands platform and off Bermuda between 2008 and 2009. Useable data were received from nine of 14 sharks tagged, tracked over a total of 529 days. Sharks spent the majority of their time making yo-yo dives within the upper 50 m of the water column and considerable time within the upper 5 m of the water column. As a result, sharks typically occupied a narrow daily temperature range (~2°C). Dives to greater than 200 m were common, and all sharks made dives to at least 250 m, with one shark reaching a depth of 828 m. Despite some similarities among individuals, a great deal of intraspecific variability in vertical habit use was observed. Four distinct depth distributions that were not related to tagging location, horizontal movements, sex, or size were detected. In addition, similar depth distributions did not necessitate similar dive patterns among sharks. Recognition of intraspecific variability in habitat use of top predators can be crucial for effective management of these species and for understanding their influence on ecosystem dynamics.
Bottom longlines are commonly used to in commercial fisheries as well as research studies sample sharks and although much attention has been focused on longline configuration (e.g. baits, hook type/size, and soak time) little information is available on the potential injury of targeted species. Sand tiger sharks (Carcharias taurus) although considered by many to be of poor food value, are highly sought after by the aquarium trade and are often encountered as bycatch in commercial fisheries. Until recently, Delaware Bay served as the one of the primary collection sites for the global aquarium trade. Due to concerns over population declines and lack of information required for proper management, the collection of sand tigers from Delaware Bay was effectively halted. In 2007 we began using standard NOAA-NMFS longline gear to collect sand tigers in Delaware Bay. An examination of our catch records suggested that the sand tigers’ feeding mechanism leads to high incidence of deep hooking (“gut hooking”) which is thought to cause injury and may impact post-release survival. In 2012, in consultation with a charter captain, we examined the influence of blocker rigs on both encounter and deep hooking rates for 267 sand tigers landed during our survey. The use of blocker rigs resulted in a nine fold decrease in the incidence of deep hooking rates. Interestingly, males were twice as likely to be captured on the control hooks compared to females although this pattern was not documented in the blocker rigs. Our results suggest that future surveys may want to employ blocker rigs as a conservation tool for shark sampling especially in areas where sand tigers are likely to be encountered.
Southern stingrays, Dasyatis americana, have been provided supplemental food in ecotourism operations at Stingray City Sandbar (SCS), Grand Cayman since 1986, with this site becoming one of the world's most famous and heavily visited marine wildlife interaction venues. Given expansion of marine wildlife interactive tourism worldwide, there are questions about the effects of such activities on the focal species and their ecosystems. We used a combination of acoustic telemetry and tag-recapture efforts to test the hypothesis that human-sourced supplemental feeding has altered stingray activity patterns and habitat use at SCS relative to wild animals at control sites. Secondarily, we also qualitatively estimated the population size of stingrays supporting this major ecotourism venue. Tag-recapture data indicated that a population of at least 164 stingrays, over 80% female, utilized the small area at SCS for prolonged periods of time. Examination of comparative movements of mature female stingrays at SCS and control sites revealed strong differences between the two groups: The fed animals demonstrated a notable inversion of diel activity, being constantly active during the day with little movement at night compared to the nocturnally active wild stingrays; The fed stingrays utilized significantly (p
Introduction Although it is widely recognized that sharks and other elasmobranchs often play a role in the transfer of energy between upper trophic levels within marine ecosystems, our understanding of the dynamics of prey consumption and processing of food in elasmobranchs remains rudimentary. To fully comprehend energy flow through elasmobranchs in marine communities it is necessary not only to know what they eat, but also to characterize the rates at which they ingest, digest, and process energy and nutrients contained in prey that is consumed. As with other areas of elasmobranch biology, investigations on dynamics of feeding and processing food lag behind such studies on other marine fishes and vertebrates. By far the most common elasmobranch feeding studies simply describe stomach contents of a particular species in a particular location. Rate of consumption, feeding patterns, and the fate of food once ingested have been examined for very few species of elasmobranchs.
- Mar 2011
1. Animal search patterns reflect sensory perception ranges combined with memory and knowledge of the surrounding environment. 2. Random walks are used when the locations of resources are unknown, whereas directed walks should be optimal when the location of favourable habitats is known. However, directed walks have been quantified for very few species. 3. We re-analysed tracking data from three shark species to determine whether they were using directed walks, and if so, over which spatial scales. Fractal analysis was used to quantify how movement structure varied with spatial scale and determine whether the sharks were using patches. 4. Tiger sharks performed directed walks at large spatial scales (at least 6–8 km). Thresher sharks also showed directed movement (at scales of 400–1900 m), and adult threshers were able to orient at greater scales than juveniles, which may suggest that learning improves the ability to perform directed walks. Blacktip reef sharks had small home ranges, high site fidelity and showed no evidence of oriented movements at large scales. 5. There were inter- and intraspecific differences in path structure and patch size, although most individuals showed scale-dependent movements. Furthermore, some individuals of each species performed movements similar to a correlated random walk. 6. Sharks can perform directed walks over large spatial scales, with scales of movements reflecting site fidelity and home range size. Understanding when and where directed walks occur is crucial for developing more accurate population-level dispersal models.
- Sep 2010
- American Fisheries Society 141st Annual Meeting
Although found globally in most temperate and tropical marine waters Delaware Bay is relatively unique as one of few locations in North America where sand tigers are commonly encountered. There are growing concerns over the trends in sand tiger abundance leading to our focus on the role of Delaware Bay in this species’ successful management. We implanted long lived acoustic transmitters in sand tigers and have been monitoring their movements via both manual and passive telemetry. Telemetered sand tigers exhibited a high degree of philopatry with 62% returning to Delaware Bay after one year of liberty and 60% returning after two years. These findings emphasize the relatively unique role that Delaware Bay plays in the life history of sand tigers. Sand tigers were resident within Delaware Bay beginning in mid May and had departed by the end of October. Unlike other large estuarine systems where sand tigers are a more transitional component of the elasmobranch community, the vast majority of telemetered individuals were regularly detected in Delaware Bay during the summer months. When combined, our findings support the key role that Delaware Bay plays in ongoing conservation and recovery efforts for sand tigers.
The Cookiecutter Shark (Isistius brasiliensis) is an ecto-parasitic predator of numerous large pelagic fish and mammals. However, little is known of its foraging ecology due to its elusive foraging tactics in the pelagic environment. We used bite scar patterns on pelagic fishes landed at the Honolulu Fish Auction to assess some of the Cookiecutter Shark foraging habits. Swordfish (Xiphias gladius) had the greatest percentage of bites (87.9 ± 25.0% of individuals had healed scars) followed by Opah (Lampris guttatus, 33.0 ± 8.3% of individuals). Most fish with scars only had one Cookiecutter Shark bite per individual with the exception of Swordfish, which often had >5 bites per individual. Furthermore, Swordfish had a higher proportion of healed bite scars meaning they had been attacked while free-swimming. Seasonal changes in the probability of hooked fish being bitten by sharks were apparent for Swordfish, Bigeye Tuna and Opah. Based on bite scar diameter, larger Cookiecutter Sharks may preferentially attack Swordfish rather than the other species of pelagic fish. When taken in conjunction with diving behavior of pelagic fish, and fishing depths, the results add further support to the hypothesis that Cookiecutter Sharks perform diel vertical migrations. KeywordsCookiecutter Shark-Longline fishery-Opah-Predation-Swordfish
Sharks face a number of obstacles for surviving their first several years of life and many species occupy nursery areas. Although estimates of survival, particularly for young age classes, are essential for assessing, monitoring and effectively managing animal populations, there have been relatively few calculations of survival within shark populations and even fewer estimates based on direct methods for sharks on their nursery grounds. We used tag-recapture methods to estimate the population size and survival of juvenile lemon sharks (Negaprion brevirostris) on their nursery grounds at Atol das Rocas, a marine protected area in Brazil. Sharks were sampled from 1999 to 2003. Population size estimates ranged from 12 to 100 juvenile sharks and survival estimates ranged between 24-54% with a mean of 44.6% over the most robust sampling periods. The population of juvenile lemon sharks declined over the course of our study, whereas survival rates may have increased over the same time period. Even a modest level of fishing and removal of mature females in adjacent areas may dramatically affect small populations of sharks within a small and isolated nursery such as Atol das Rocas. The lower survival rates and population size at Atol das Rocas could be the result of differences in physical characteristics of this nursery in comparison to others used by lemon sharks in the northwestern Atlantic. Such comparatively lower populational parameters suggest that the population of young lemon sharks is fragile at the Atol das Rocas nursery.
The diet and daily ration of the shortfin mako (Isurus oxyrinchus) in the northwest Atlantic were re-examined to determine whether fluctuations in prey abundance and availability are reflected in these two biological variables. During the summers of 2001 and 2002, stomach content data were collected from fishing tournaments along the northeast coast of the United States. These data were quantified by using four diet indices and were compared to index calculations from historical diet data collected from 1972 through 1983. Bluefish (Pomatomus saltatrix) were the predominant prey in the 1972-83 and 2001-02 diets, accounting for 92.6% of the current diet by weight and 86.9% of the historical diet by volume. From the 2001-02 diet data, daily ration was estimated and it indicated that shortfin makos must consume roughly 4.6% of their body weight per day to fulfill energetic demands. The daily energetic requirement was broken down by using a calculated energy content for the current diet of 4909 KJ/kg. Based on the proportional energy of bluefish in the diet by weight, an average shortfin mako consumes roughly 500 kg of bluefish per year off the northeast coast of the United States. The results are discussed in relation to the potential effect of intense shortfin mako predation on bluefish abundance in the region.
Movement patterns and habitat use of juvenile lemon sharks Negaprion brevirostris were monitored at Atol das Rocas, Brazil, an atypical nursery area for this species, characterized by extreme tides and a lack of seagrass flats and mangroves. Twenty-three sharks carrying transmitters were monitored using an array of bottom-fixed automated receivers during 3 trips over a total of 60 d. Transmitters were recorded on receivers over 13 000 times, and the majority of sharks were detected more than 100 times. Newborn sharks (60 to 80 cm total length, TL) showed restricted but repeated movements between small tide pools on reef flats at low tide and a small, shallow, nearby tidal creek at high tide. Larger sharks (up to 106 cm TL) sampled 6 and 20 mo after the study in March 2000 frequented the tidal creek and several other locations at high tide and a variety of larger pools at low tide, and in general exhibited more extensive movements within the atoll than did newborn sharks. Sharks approaching 2 yr of age were generally observed in specific pools or shallow water locations within the atoll during high and low tides, but also expanded their movements to include more of the atoll. Throughout the study, young lemon sharks appeared to concentrate movements within shal- low-water low-tide refuges and separate high tidal areas. Movement patterns of sharks in Atol das Rocas differ from those at other well-studied lemon shark nursery locations, where individuals con- tinuously occupy shallow flats and mangrove habitats. Nevertheless, lemon sharks in general restrict their movements to shallow-water habitats regardless of the specific nursery area occupied. This behavior is most likely related to predator avoidance. This study provides an example of the inter- action between the physical environment and the biology of animals—in this case, the influence of the physical characteristics of a nursery area and the behavioral ecology of young lemon sharks.
Habitat of juvenile Caribbean reef sharks, Carcharhinus perezi (Carcharhinidae), was identified using fishing surveys and capture of immature specimens at two Brazilian insular sites in the southwestern Atlantic Ocean, Fernando de Noronha Archipelago and Atol das Rocas. Standardized sampling at Fernando de Noronha indicated that parturition occurred from February to April and that a wide depth-range (at least 5–30 m) along the insular shelf was used by immature sharks throughout the year. The catch-per-unit effort of C. perezi was significantly higher inside than outside a marine protected area at this location, suggesting that these sharks are more common in parts of the reef least disturbed by human activities. More limited sampling at Atol das Rocas suggested that juvenile C. perezi occurred at similar depths and utilized similar substrate as sharks at Fernando de Noronha. These findings suggest that successful conservation and management of this economically important, protected species will need to include conservation of habitat around insular reef systems.
Competition and predation are both important in structuring the distribution of marine organisms; however, little is known about how competition and predation influence the distribution of elasmobranch fishes. We used data collected from shark control programs conducted between 1967 and 1980, throughout the Hawaiian island chain, to examine the distribution and dietary over- lap of the 4 most abundant carcharhinid sharks. Tiger sharks Galeorcerdo cuvier and Galapagos sharks Carcharhinus galapagensis were caught at all islands, but were more abundant in the north- western Hawaiian Islands (NWHI) than in the main Hawaiian Islands (MHI). Gray reef sharks Carcharhinus amblyrhynchos and sandbar sharks Carcharhinus plumbeus showed an inverse rela- tionship in distribution, with sandbar sharks abundant in the MHI, but virtually absent throughout the NWHI, and gray reef sharks only sporadically found throughout the MHI, but abundant in the NWHI. Dietary overlap was high between gray reef and sandbar sharks, and between sandbar and Galapagos sharks. Tiger sharks had low dietary overlap with all other species, except for large Gala- pagos sharks. The data analyzed in our study support the hypothesis that interspecific competition influences the distribution of carcharhinid sharks throughout the Hawaiian Archipelago.
The sandbar shark, Carcharhinus plumbeus, is a wide-ranging coastal species in tropical and temperate regions, and it is the most common species of shark in Hawaii, as in many locations where it occurs. Information on the diet and feeding habits of this species in the Pacific Ocean are extremely limited. For this study we quantified the diet of sandbar sharks in Hawaii based on records collected during the Hawaii Cooperative Shark Research and Control Program from 1967 to 1969. During this program a total of 565 stomachs were examined, of which 265 contained food. Sharks ranged in size from 59 to 190cm total length. Teleosts were the most common prey group, but both cephalopods and crustaceans also occurred frequently. Ontogenetic changes in diet of sandbar sharks were apparent, with crustaceans forming a greater proportion of the diet of smaller sharks. Both cephalopods and elasmobranchs increased in importance with increasing shark size. Prey diversity also increased with size, with large, mobile, and reef prey species found more commonly in the diet of larger sharks. Mature male and female sharks appeared to segregate by depth, though major differences in the diet between the sexes were not apparent. However, there was some evidence of dietary differences between sharks caught in different depths and seasons. The results of this study suggest that sandbar sharks in Hawaii and throughout the world, are primarily piscivores, but also consume a variety of invertebrate prey, and that their diet varies with geographical location and stage of development.
- May 2006
Lemon sharks Negaprion brevirostris were sampled in the Atol das Rocas, a nursery area, on nine occasions from March 1999 to October 2003, during which 157 individuals were tagged and 35 were recaptured. The male : female sex ratio of captured individuals was 1 : 1Á12. Mean AE S.D. growth rates were 24Á7 AE 3Á4 cm year À1 in total length (L T), 20Á7 AE 3Á2 cm year À1 in fork length, and 19Á5 AE 2Á7 cm year À1 in precaudal length. There was no significant difference in growth rates between males and females. Mean AE S.D. increase in mass was 2565 AE 762 g year À1 . The von Bertalanffy growth parameters estimated by the Fabens method based on L T were: k ¼ 0Á077, L 1 ¼ 399Á9 cm and t 0 ¼ À2Á16. Despite the large variation of environmental conditions, parti-cularly of tidal range and currents, and the lack of protective mangrove cover in the nursery area at Atol das Rocas, juvenile lemon sharks grew relatively faster than at other nurseries. Such rapid growth could be a response to abundant food availability or high risk of predation by adults that enter the nursery area.
The Northwestern Hawaiian Islands (NWHI) host a variety of large vertebrate animals including seabirds, green sea turtles (Chelonia mydas), Hawaiian monk seals (Monanchus schauislandi), and large teleost fish such as trevally (Family Carangidae) and several species of sharks. The air-breathing vertebrates have been the subjects of relatively continuous and well-funded research programs over the past several decades, and many aspects of their biology in the NWHI have been documented fairly well. However, studies directed at understanding the biology and ecology of large teleost fishes and sharks in the NWHI have lagged substantially behind research conducted on birds, turtles and seals. In the summer of 2000, an array of autonomous acoustic receivers was deployed at French Frigate Shoals (FFS) in the NWHI as part of a project investigating the movement patterns of tiger sharks (Galeocerdo cuvier) within the atoll, particularly in relation to the high seasonal abundance of potential prey (birds, turtles, seals). Shortly after the establishment of the initial array of monitors in 2000, additional monitors were deployed in an effort to monitor the movements of Galapagos sharks (Carcharhinus galapagensis) at FFS, particularly at locations where monk seal pups had been preyed upon by these sharks. The scope of the monitoring study was further expanded to Midway Atoll during summer of 2001 to monitor movements of Galapagos sharks near seal haul-out beaches and to examine survivorship and behavior of giant trevally (Caranx ignobilis) captured and released in a commercial sport fishing operation conducted within the Midway National Wildlife Refuge. For each study, experimental animals were captured and surgically fitted with long-life, individually-coded acoustic transmitters. During nearly 4 years of acoustic monitoring at FFS and 2 years of monitoring at Midway, a total of over 45,000 detections of sharks and fish with transmitters were recorded on acoustic monitors. These data enable an assessment of long-term movement patterns of these large predators within the NWHI. Each species investigated demonstrated somewhat repeated and predictable behavioral patterns that provide a basis for improved understanding of determinants of behavior and for enhanced management of these animals and prey (birds, seals, turtles) with which they may interact.
The movement patterns and long-term site-fidelity of primarily juvenile Caribbean reef sharks, Carcharhinus perezi, were investigated using tag-recapture and automated telemetry at an insular nursery area, the Fernando de Noronha Archipelago, Brazil. Of the 143 externally tagged juvenile sharks (<110cm), 22 (15.3%) were recaptured between 0 and 5km from the site of tagging after 5–800days at liberty, suggesting some site-fidelity in young individuals of this species. Site-fidelity and movement patterns of ten juvenile sharks ranging from 78 to 110cm total length (TL) and one opportunistically captured adult female (224cm TL) were also investigated for periods of up to 2years with an array of automated telemetry receivers. Tagging and telemetry data from both inside and outside a marine protected area (MPA) show that shark abundance and activity is greatest along the part of the archipelago’s coastline least disturbed by human activity. Telemetry tracking also showed that juvenile reef sharks demonstrated a high degree of site-fidelity and occupied specific locations along the coast throughout the year, with some evidence of an increase in activity space with ontogeny. Sharks appeared to range more widely at night and there were no seasonal variations in habitat use. Our results suggest that MPAs may be a useful conservation tool to protect young C. perezi and potentially other reef-dwelling carcharhinid sharks during their early life history.
Movement patterns, site fidelity and growth were studied for giant trevally (Caranx ignobilis) inhabiting a marine reserve surrounding Coconut Island in Kaneohe Bay, off the Island of Oahu, Hawaii. Short-term movements of fish were determined by acoustic telemetry and long-term movements and growth were investigated with conventional tag and release methods. Giant trevally appear to move to the Coconut Island marine reserve from the adjacent bay floor upon attaining a size of approximately 20–25 cm fork length. After several years spent frequenting the reserve, giant trevally move out of the bay into deeper water. Tracked fish spent considerable time within the marine reserve moving along the reef slope, but frequently ventured outside of the reserve boundaries. The recapture rate for tagged fish was 11%, with an average time at liberty of 346 days. Nearly one-third of recaptured fish were caught at distances greater than 3 km from the tagging site with maximum values demonstrating long-term (more than 7 years) and long-distance (30 km) movements. The protective function of the Coconut Island marine reserve for giant trevally is limited because the reserve is utilized by only a portion of the population, and even these fish regularly move outside of the refuge.
We investigated short-term movements of neonate and juvenile sandbar sharks, Carcharhinus plumbeus, on their nursery grounds in Delaware Bay. The majority of sharks tracked limited their movements to water less than 5m deep, remained within 5km of the coastline, and occupied oblong activity spaces along the coast. In addition to site-attached coastal movements observed, several sharks moved entirely across Delaware Bay or spent considerable time in deeper portions of the central bay. Sharks tracked on the New Jersey side of the bay tended to spend more time in deeper water, farther from shore than sharks tracked on the Delaware side. Observation-area curves estimated that optimal tracking time for sandbar sharks in Delaware Bay was 41h. Indices of site attachment showed that movement patterns of tracked sandbar sharks varied from nomadic to home ranging. There was no significant difference in rate of movement for day/night, crepuscular periods, or between juveniles and neonates. In general, young sandbar sharks patrolled the coast and appeared to be site attached to some extent, but were capable of making longer excursions, including movement entirely across Delaware Bay.
The Hawaiian stingray, Dasyatis lata, is a common benthic elasmobranch in nearshore Hawaiian waters. Acoustic telemetry was used to track the movements of seven rays in Kaneohe Bay, Oahu, Hawaii. Rays were tracked continuously over 31-74 h periods. Geographical movements were analyzed to determine space utilization and rate of movement. Rays were found to utilize significantly larger activity spaces at night (0.83ǂ.70 km2) (mean-SD) than during the day (0.12ǂ.15 km2). Mean total activity space for rays tracked was 1.32ǂ.75 km2. Rates of movement were also significantly higher at night (0.34ǂ.30 km h-1) than during the day (0.15ǂ.22 km h-1). Average straight-line swimming speed was 0.64ǂ.16 km h-1, with a maximum observed swimming speed of 1.9 km h-1. Tidal stage had no effect on rate of movement. Comparison with previously published data on juvenile scalloped hammerhead sharks, Sphyrna lewini, in Kaneohe Bay revealed a high degree of overlap in habitat use and time of activity, suggesting possible ecological interactions between these two species.
Stomach content, capture method and capture location data were collected for 401 carangids captured during three annual 1-day fishing tournaments held at a coastal bay in Hawaii. Blue jack (Caranx melampygus), white jack (Caranx ignobilis) and island jack (Carangoides orthogrammus) were the most common species, accounting for 83.5, 8.5 and 5.2% of tournament catches, respectively. Geographical area fished consisted of a sheltered bay and the adjacent seaward coastal reef beyond. Area of capture and fishing method influenced species and size of fish captured. Small (<350 mm fork length) C. melampygus and C. ignobilis predominated in catches within the sheltered embayment indicating this may serve as a nursery area for these species. Conversely most C. orthogrammus and all large (>500 mm) C. melampygus were captured outside Kaneohe Bay. Trolling (towing a surface lure) accounted for 80% of C. melampygus, 76% of C. orthogrammus and 55% of C. ignobilis captured. Differential vulnerability to trolling may be related to interspecific differences in diet; captured C. melampygus had fed primarily on fish whereas C. orthogrammus had consumed both fish and benthic crustaceans, and C. ignobilis had eaten mainly benthic crustaceans. Differences in diet may indicate resource partitioning between these sympatric and closely related species. For C. melampygus there was a consistent relationship between prey size and predator size. When conducted under scientific scrutiny, fishing tournaments can provide synoptic data on diet and gear vulnerability that would otherwise be very difficult to obtain.
Sandbar shark (Carcharhinus plumbeus) populations on the US east coast have undergone several decades of decline due to fishing pressure. One strategy for rebuilding stocks is improved survival of young sharks through enhancement of nursery areas. A key element for understanding the dynamics of shark nursery areas is increased knowledge about essential habitat for young sharks that occupy these nurseries. This study was conducted to quantify habitat use and movement patterns of juvenile sandbar sharks in Delaware Bay, which is a major east coast nursery for this species. Twenty five sandbar sharks were tracked for 2.5 to 75 h using ultrasonic telemetry. Although the sharks moved throughout the lower portion of the bay, and several sharks crossed the entire bay, individuals predominantly remained close to shore and in shallow water. The majority of sharks tracked showed movements that were heavily influenced by tidal currents, and sharks tracked on the New Jersey side of the bay had larger activity spaces, occupied deeper water, and ranged farther from shore than sharks tracked on the Delaware side. Management measures such as area/time closures would provide protection for a large number of sharks in a relatively small portion of Delaware Bay and may be improved if behavior of sharks is taken into consideration. For example, area closures on the Delaware side of the bay are likely to protect more individuals per unit area than an equal area on the New Jersey side. Our study demonstrates the utility of telemetry studies for providing information that will allow more precisely focused and effectively implemented fisheries management practices.
- Jan 2001
- Electronic Tagging and Tracking in Marine Fisheries
Five different types of tags were used to monitor the horizontal and vertical movement patterns of tiger sharks and to document site fidelity. Sonic tracking experiments gave insight into the fine-scale movement patterns of the sharks for periods of up to 50 h whereas long-lived, acoustic pingers and automated, anchored data loggers (listening posts) provided data regarding the long-term periodicity and frequency of return of tiger sharks. These electronic recaptures were compared with the rate of traditional recaptures of sharks tagged with standard dart tags and recaptured with fishing gear. In the most recent phase of research, archiving tags capable of downloading stored data via sonic modem technology (CHAT tags) were implanted in sharks. The characteristics of data derived from these tags were compared with data acquired by active sonic tracking. A single pop-up satellite tag was provided to the shark tracking project by the manufacturer. This tag was attached with a saddle fitted around the anterior edge of the dorsal fin of a shark. Again, the active sonic tracking data were used to evaluate the veracity of the data acquired form the satellite tag. Data from these various sources are beginning to paint a consistent picture of tiger shark home range size and site fidelity in the Hawaiian archipelago.
Suitability of small (km2) marine reserves for protecting a commercially important endemic Hawaiian goatfish, Parupeneus porphyreus, was examined by quantifying goatfish habitat use, home range size and site fidelity in an existing marine reserve (Coconut Island in Kaneohe Bay, Hawaii). Five goatfish equipped with acoustic transmitters were tracked for up to 93h each over 3–14 days. Daytime habitat use patterns of two of these fish were continuously monitored for one month using a fixed hydrophone hardwired to an onshore computer. Acoustically tagged fish showed consistent diel patterns of behavior, refuging in holes in the reef by day and moving over extensive areas of sand and coral rubble habitat at night. Remote monitoring of daytime habitat use by two goatfish revealed that the same daytime refuge was used by both fish for at least one month (the battery life of the transmitters). Home ranges of all fish were within the boundaries of the Coconut Island reserve suggesting that even small areas containing suitable habitat can make effective reserves for this species. A relatively low abundance of reproductive size P. porphyreus at Coconut Island in comparison with deeper areas may indicate an ontogenetic shift to deeper habitat in this species.
Deep-sea sharks approach neutral buoyancy by means of a large liver that contains large amounts of low-density lipids, primarily squalene and diacyl glyceryl ether (DAGE). As an animal increases in size and matures sexually, many biochemical changes take place within the animal. It was hypothesized that maintenance of neutral buoyancy in deep-sea sharks involves fine-scale changes in the chemical composition of the liver oil as individual sharks grow and develop. To test this hypothesis, the lipid composition of liver oil for individuals of different size and sex of deep-sea sharks from the Chatham Rise, New Zealand was compared. The composition of liver oil varied within and among species. Several species contained large amounts of squalene and DAGE, whereas only traces of these lipids were present in other species. The amounts of squalene and DAGE in liver oil were inversely related, and squalene content tended to decrease as sharks increased in size. Species with high squalene levels (>80%) in liver oil were not abundant on the Chatham Rise, although levels of DAGE (a lipid of increasing commercial interest) were elevated in many species. Maintenance of neutral buoyancy in deep-sea sharks appears to involve changes in the composition of low-density liver lipids as the sharks increase in size and mature.
The distribution and abun- dance of deep-sea sharks on Chatham Rise, New Zealand, are described. Sharks were collected as bycatch in two deep-water trawl fisheries at a total of 390 stations, which ranged in depth from 740 to 1503 m. Sixteen species of shark were caught; Deania calcea, Centroscymnus crepidater, Etmopterus granulosus, and Centroscymnus owstoni accounted for the largest portion of the shark catch. Species that would provide the highest yield of commer- cially important liver lipids were not abundant in trawls. All sharks com- bined formed only 4.2% of overall bio- mass captured in trawls. Depth is a major determinant of the composition of the shark assemblage; both density of sharks (kg/km2) and species diversity were inversely proportional to depth. Distributional patterns of the shark community varied with location on Cha- tham Rise, and species composition of the shark catch varied with the spe- cies of teleost targeted in deep-water trawls. Sharks are common bycatch in deep water fisheries around the world, forming as much as 50% of the catch in deep-sea trawls in areas such as New Zealand and Austra- lia (Deprez et al., 1990; Clark and King1). Most sharks captured in the New Zealand and Australian deep- water fisheries are dead by the time they are brought to the surface and are discarded, but some sharks are retained for their liver oil. In Japan and Australia, several species of deep-sea shark in the family Squal- idae are targeted in fisheries and their liver oil is utilized. Although the short-term potential of fisheries directed towards deep-sea sharks
The first occurrence of the rare viper shark, Trigonognathus kabeyai, from the central Pacific Ocean is reported. Morphometries are compared between this specimen and the type specimens from Japan, and this specimen differs from the types in only a few measurements. The poor preservation of this specimen precluded examination of internal anatomy.
Externally and internally implanted sonic transmitters were used to track the movements of eight tiger sharks (Galeocerdo cuvier) ranging between 200 and 417 cm total length (TL), captured by hook-and-line on the south coast of Oahu, Hawaii, between 1993 and 1997. Attachment of the transmitters was facilitated by the fact that captured sharks exhibited tonic immobility when restrained and inverted at the side of the tagging vessel. Three common themes emerged from the horizontal movements of the tracked sharks: (1) offshore movements away from the island, (2) extended periods of directed, “straight-line” swimming, (3) orientation to the Penguin Banks – a shallow bank located ≃35 km from the release point. In shallow water (<300 m) the sharks swam predominantly close to the bottom, in open water (>300 m) they swam within the mixed layer at depths of ∼80 m. One shark dove briefly to 335 m. The average estimated swimming speed of sharks traversing open water was 0.29 body length (BL) s−1. Two sharks were recaptured after termination of the tracks; one of these sharks was recaptured twice, with a total time at liberty of 377 d. The data suggest that Hawaiian tiger sharks move within large home ranges and that they can efficiently navigate between distant parts of their range, even when this requires crossing open ocean waters.
Distribution, reproduction, and diet of the gray reef shark Carcharhinus amblyrhynchos were investigated using data collected during shark control programs in the main Hawaiian Islands (MHI) and during research fishing in the Northwestern Hawaiian Islands (NWHI). A total of 472 sharks were caught between 1967 and 1980. These sharks have a restricted distribution in the MHI; they were collected only in the vicinity of Niihau and Molokini islands, but were one of the most abundant sharks throughout the NWHI. Catch rate was higher for males than for females in standard longline fishing at all locations and during all seasons. Most sharks were caught at depths between 20 and 60 m, and depth distribution of the sexes was similar, although females were more common at shallower depths. Males ranged in size from 79 to 185 cm total length (TL), and matured at between 120 and 140 cm TL. Females ranged in size between 63 and 190 cm TL and matured at about 125 cm TL. Litter size ranged from 3 to 6, with an average of 4.1 pups. Size at birth was estimated to be just over 60 cm TL. Most sharks (85%) consumed teleosts, but some fed on cephalopods (29.5%), and crustaceans (4.9%). For sharks in the largest size classes, the frequency of occurrence of teleosts declined, whereas that of cephalopods increased.
Distribution, population structure and reproduction are described for the southern lantern shark Etmopterus granulosus at the Chatham Rise, New Zealand. Depth of capture for E. granulosus ranged from 744 to 1420 m, with highest catch rates between 800–1200 m. More than twice as many females as males were captured, and the majority of sharks caught were mature, indicating that there may be segregation according to sex and size class. Only 10 of 492 female sharks captured contained ova in uteri, and none contained embryos. The absence of pregnant females suggests that they move to another area or depth prior to pupping. Size of sharks captured ranged from 20·0 to 78·8 cm total length. Females began to mature at 62 cm total length, and males at 52 cm. There was no evidence of a seasonal reproductive cycle. Ovulation appeared to occur when ova reached a diameter of 40–45 mm. The average number of ova in mature females was 12·7. This information is crucial for assessing the impact of fisheries on E. granulosus populations.
Stomach content data from 281 tiger sharks caught during shark control programs in Hawaii between 1967 and 1969, and during 1976 were analyzed to examine feeding habits and ontogenetic shifts in diet. As sharks increased in size, prey diversity and frequency of occurrence of large prey items increased. The percent occurrence of teleosts and cephalopods in stomachs decreased as sharks increased in length, while occurrence of elasmobranchs, turtles, land mammals, crustaceans, and undigestible items increased. Comparisons between the diets of tiger sharks from Hawaii and other locations indicate that ontogenetic shifts are universal in this species and that tiger sharks may be opportunistic feeders that prey heavily on abundant, easy to capture prey. Small tiger sharks may be spatially segregated from medium and large sharks and appear to be primarily nocturnal, bottom feeders. Large tiger sharks feed near the bottom at night, but also feed at the surface during the day. Prey, similar in size to humans, begin to occur in the diet of tiger sharks approximately 230 cm TL, and therefore sharks of this size and larger may pose the greatest threat to humans. Ontogenetic shifts in diet may be attributed to increased size of sharks, expanded range and exploitation of habitats of larger sharks, and/or improved hunting skill of larger sharks.
This paper summarizes records from longline fishing programs conducted in Hawai'i between 1959 and 1980. Data from 11 species of sharks (173 individual sharks) are reported and compared with worldwide records. Although much of the data is nearly 30 yr old, the information was never fully utilized and represents the following important findings. The relationship between clasper length and total length (TL) for bluntnose sixgill shark, Hexanchus griseus (Bonnaterre), indicates that males mature at about 309 cm TL. High fecundity (114 pups) is reported for the prickly shark, Echinorhinus cookei Pietschmann. The smallest mature male E. cookei (183 cm TL) and the smallest pregnant (205 cm TL) bignose shark, Carcharhinus altimus (Springer), are recorded. New maximum depth of capture records for the blacktip shark, Carcharhinus Umbatus (Valenciennes), at 64 m, and for the smooth hammerhead shark, Sphyrna zygaena (L.), at 68 m, are also documented. Distributions of deep-sea sharks in Hawai'i appear to be associated with isothermic submergence, and the sharks remain below the thermocline (100-400 m) and in water temperatures of 9-12°C. Carcharhiniform sharks in Hawai'i range to greater depths than reported elsewhere; this appears to be correlated with the Tropics having warmer water temperatures (20-26°C), which extend down to 100-400 m in depth.
The short-and long-term movement patterns of blue trevally (Caranxmelampygus) were monitored using a combination of sonic tracking and tag-and-release techniques. All fish were captured and released on the patch reef surrounding Coconut Island in Kaneohe Bay, Oahu, Hawaii, which has been a no-fishing conservation zone for over 30 years. Sonic tracking produced fine-scale movement data from five fish for periods spanning up to 18 days. All fish displayed die1 movement patterns within consistent home ranges, which encompassed different parts of the reef during the night than during the clay. Movements were predominantly along the walls of the patch reef, with occasional forays to nearby sections of adjacent reefs. Four hundred and ten fish were tagged and released on the Coconut Island reef, and the recapture sites of 85 recaptured fish indicated that most did not move far from their point of release; 75.5% were recaptured within 0.5 km of their release points. Time at liberty ranged from 4 to 454 days, and distance between release and recapture sites was not related to time at liberty. Some fish were observed many times in the same areas over periods of several months. Both the tracking and recapture data indicate strong site fidelity in this species and low occurrence of long distance emigration. These behavioral traits suggest that successful husbandry of this species may be accomplished through the use of management practices such as establishing no-fishing zones.
Catch records from the Hawai''i Cooperative Shark Research and Control Program, which operated in Hawai''i from 1967–1969, were examined and data on the Galapagos shark,Carcharhinus galapagensis were analyzed. A total of 304 Galapagos sharks was caught, predominantly with longlines. More female sharks were caught than males, and the catch was skewed geographically. On the island of O''ahu the highest catch rates occurred along the north and south coasts. High catch rates also occurred near points of land, where longshore currents converge. Average depth of capture was greater for juveniles (45.1 m) and mature males (60.2 m), than for subadults (38.8 m) and mature female sharks (34.2 m). Males appear to reach maturity between 205 and 239 cm total length, and females between 215 and 245 cm. Litter size ranged from 4 to 16 pups, with an average of 8.7. In Hawaiian waters Galapagos sharks are born at just over 80 cm total length. Mating and parturition apparently occur early in the year, and gestation is estimated to be about 12 months. Stomach contents consisted mainly of teleosts and benthic prey, and ontogenetic changes in diet occurred as sharks increased in size. Sharks consumed a smaller proportion of teleosts and more elasmobranchs with increasing size. Dietary diversity also increased with increasing size of shark.
- Jan 1996
The short- and long-term movement patterns of blue trevally (Caranxmelampygus) were monitored using a combination of sonic tracking and tag-and-release techniques. All fish were captured and released on the patch reef surrounding Coconut Island in Kaneohe Bay, Oahu, Hawaii, which has been a no-fishing conservation zone for over 30 years. Sonic tracking produced fine-scale movement data from five fish for periods spanning up to 18 days. All fish displayed diel movement patterns within consistent home ranges, which encompassed different parts of the reef during the night than during the clay. Movements were predominantly along the walls of the patch reef, with occasional forays to nearby sections of adjacent reefs. Four hundred and ten fish were tagged and released on the Coconut Island reef, and the recapture sites of 85 recaptured fish indicated that most did not move far from their point of release; 75.5% were recaptured within 0.5 km of their release points. Time at liberty ranged from 4 to 454 days, and distance between release and recapture sites was not related to time at liberty. Some fish were observed many times in the same areas over periods of several months. Both the tracking and recapture data indicate strong site fidelity in this species and low occurrence of long distance emigration. These behavioral traits suggest that successful husbandry of this species may be accomplished through the use of management practices such as establishing no-fishing zones.
In an attempt to allay public fears and to reduce the risk of shark attack, the state government of Hawaii spent over $300,000 on shark control programs between 1959 and 1976. Six control programs of various intensity resulted in the killing of 4,668 sharks at an average cost of $182 per shark. The programs furnished information on diet, reproduction, and distribution of sharks in Hawaii, but research efforts of the programs had a number of shortcomings. Analysis of the biological data gathered was not directed toward the tiger shark, Galeocerdo cuvier (Peron & LeSueur), which is responsible for most attacks in Hawaii. Reliable estimates of shark populations in Hawaii cannot be made based on catch data from control programs because of sampling biases. Most of the information gained from the control programs was not published in reviewed journals and is not readily available to the scientific community. The ability of the control programs to reduce shark populations and to remove large sharks from coastal waters appears to have been stated with more confidence than is warranted, considering seasonal changes observed in shark abundance and variable fishing effort. Shark control programs do not appear to have had measurable effects on the rate of shark attacks in Hawaiian waters. Implementation of large-scale control programs in the future in Hawaii may not be appropriate. Increased understanding of the behavior and biology of target species is necessary for evaluation of the effectiveness of small-scale control efforts, such as selective fishing after an attack. Acoustic telemetry, conventional tagging, and studies on population dynamics concentrating primarily on the tiger shark may be used to obtain data about activity patterns, distribution, and population parameters, providing information useful for reducing the risk of shark attack in Hawaii and elsewhere.
The suitability of acid-insoluble ash as a marker in digestive efficiency studies with the lemon shark (Negaprion brevirostris) was investigated. Acid-insoluble ash concentration in the experimental diet was increased by adding celite (diatomaceous earth). Acid-insoluble ash was palatable to test animals, mixed homogeneously within the experimental diet, could be easily and precisely quantified in feces and food, and was not produced by lemon sharks. However, acid-insoluble ash content in feces was significantly lower during the first 24 h of fecal production than during subsequent collection periods, and the marker may not have remained uniformly mixed in digesta. Differential passage rates for this marker and food may influence estimates of absorption efficiency. Passage rate of acid-insoluble ash should be investigated in future studies of digestive efficiency when this marker is used.
The efficiency with which the lemon shark, Negaprion brevirostris, is able to absorb energy, organic matter, and dry matter was measured at five levels of energy intake. An indirect method was used by incorporating celite, an inert reference substance, into food. Absorption efficiencies ranged from 62-83% for energy, 76-88% for organic matter, and 76-87% for dry matter. Absorption efficiencies increased as energy intake increased but declined at the highest level of intake. Fecal composition varied little throughout the digestive process, and absorption efficiency did not depend on time of fecal collection. Absorption efficiency was overestimated based upon a total fecal collection method. To our knowledge, these are the first measurements of absorption efficiency reported for any species of elasmobranch and demonstrate that the lemon shark is as capable as carnivorous teleosts of efficiently absorbing nutrients from food.
Ultrasonic telemetry was used to determine the movements and distribution of juvenile hammerhead sharks (Sphyrna lewini) on their natal grounds in Kaneohe Bay, Oahu, Hawaii. Transmitters were force fed to six pups which were tracked for periods of up to 12 days. All animals showed a high fidelity to a shared daytime core area to which they repeatedly returned after exhibiting wider ranging nocturnal movements. During daytime, the shark pups formed a loose school which moved about within the core area, hovering about 1.5 m off the bay floor. This daytime refuging behavior may serve an antipredation function. Nighttime movements covered the bay floor and bases of patch and fringing reefs and probably represented foraging excursions. Occasional forays away from the core area also occurred during daytime. The small size of the total activity spaces may indicate a healthy forage base for the sharks. Nocturnal swimming speeds were greater than diurnal swimming speeds.
The movements, growth rates and distribution of a population of white goatfish Mulloides flavolineatus were investigated using a combination of tag-and-release and sonic tracking techniques. The study site was a 137 km2 patch reef which has been a no-fishing conservation zone for over 30 years. The population showed high site fidelity; 93% of recaptures occurred at the release site, with times at liberty of up to 531 days. Tracking revealed crepuscular movements away from daytime schooling sites to consistent nighttime foraging grounds up to 600 m away. The route taken between daytime and nighttime habitats was the same each night. Suround-net quadrats were used to measure goatfish densities on the nighttime feeding grounds. The high site fidelity and limited range of diel movements of these fish indicate that quite small harvest refugia can serve to effectively protect populations of mature adults, and that for most of the year, emigration of adults into adjacent fisheries was minimal.
Fecal production was monitored to observe the effects of meal size on retention time of food in the digestive tracts of lemon sharks, Negaprion brevirostris. Initial appearance of feces occurred more rapidly when ration level was increased. The onset of fecal production was negatively correlated with rate of intake. Production of feces continued for a longer period of time when meal size was increased. Retention time of food was directly related to feeding rate, suggesting that the rate of digestion was constant. The correlation between retention time and intake on a percentage body weight basis was greater than the correlation between retention time and intake on an energy density basis. The use of agar to bind food may have delayed digestion and prolonged food passage for sharks fed an experimental diet.
Though the diets of many species of sharks have been described, little information exists about patterns of food intake and about the fate of prey items once they are ingested. Digestive physiology and efficiency of elasmobranchs are generally accepted as similar to those of teleosts, although digestive morphologies of the two groups differ. The lemon shark, Negaprion brevirostris, has been the subject of a series of studies examining characteristics of consumption and digestive processing of food. Diet of young lemon sharks and many other sharks is dominated by teleosts. Feeding by lemon sharks is asynchronous, intermittent, and exhibits no pattern of periodicity. A meal is completely evacuated from the stomach of lemon sharks 25-41 hours after feeding, depending on meal type and temperature. Fecal production continues for.68-82 hours after feeding in the lemon shark. A relatively long period of time is also required for digestive processing of food in other species of sharks. Lemon sharks absorb energy from food with an efficiency similar to that of most teleosts. Daily ration has been estimated at 1.5-2.1% body weight/day, which is intermediate in comparison to estimates for other species of sharks and which is low in comparison to most teleosts. Lemon sharks are able to convert ingested energy to energy stored as growth as efficiently as many teleosts. Slow rates of digestion and consumption arc factors which probably limit growth in the lemon shark and other elasmobranchs. Our findings for the lemon shark arc compared with information gathered for other species of sharks.
The time required for a meal to be completely eliminated from the digestive tract of the lemon shark Negaprion brevirostris was determined X-radiographically, with barium sulfate as a contrast medium. Two food markers and X-radiography showed that initial voidance of fecal matter began 16–17 h after feeding. Alimentary tracts emptied completely within 68–82 h after food ingestion. Passage of a meal through the digestive tract took substantially longer than in most teleosts. A slow rate of food passage may contribute to the low consumption of food and slow growth that have been observed for the lemon shark.
Movement patterns of juvenile sandbar sharks in Delaware Bay were investigated with acoustic telemetry. Thirteen sharks were tracked for between 6-70 h during June-September, 1998. Movements were closely related to tidal currents and most sharks spent the majority of time within 3 km of shore and in water 2-5 m deep. Two sharks ranged further afield and one of these crossed the bay from DE to NJ.
Thesis (Ph. D.)--University of Hawaii at Manoa, 1998. Includes bibliographical references. Microfiche.