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Overlap between highly suitable habitats and longline gear management areas reveals vulnerable and protected regions for highly migratory sharks
Abstract
Highly migratory species (e.g. sharks, tunas, turtles, cetaceans) present unique conservation
management challenges due to their wide-ranging movements. Consequently, the
extent to which management areas protect habitats for highly migratory species is often unknown. Within the southeast region of the USA’s exclusive economic zone, highly migratory sharks are target and/or bycatch species in pelagic and bottom longline fisheries. Here, we developed maximum entropy habitat suitability models for great hammerhead sharks Sphyrna mokarran, tiger sharks Galeocerdo cuvier, and bull sharks Carcharhinus leucas within the southeast region based on satellite tag (n = 96) and remotely sensed environmental data. Modeled highly suitable habitats were compared to longline gear management areas to determine what proportion of these habitats are protected from, and vulnerable to, longline fisheries. The percentages of highly suitable habitats overlapping with longline management areas varied by species and season (78% warm, 36% cool season for great hammerhead sharks; 48% warm, 79% cool for tiger sharks; and 2% warm, 100% cool for bull sharks). Highly suitable great hammerhead and tiger shark habitats were relatively well protected from pelagic longline fisheries yet vulnerable to bottom longline fisheries. Additionally, both species were vulnerable to pelagic and bottom longline fisheries off southwestern Florida; thus, extending gear restrictions to this area may benefit both species. Bull shark highly suitable habitats were only well protected from longline gear during the cool season. These results demonstrate how habitat suitability modeling can be used to help assess the efficacy of spatial management strategies and inform conservation plans for highly migratory species.
... Understanding climate-driven effects on the movement ecology of tiger sharks has been identified as a research priority for this apex predator (Holland et al., 2019). In the western North Atlantic, tiger sharks are relatively well protected from commercial fisheries due to high spatial overlap between their home range and management zones that prohibit commercial longline fishing (Calich et al., 2018;Graham et al., 2016;Queiroz et al., 2019). However, the waters encompassing the northerly portions of their home range are experiencing among the fastest rates of ocean warming globally (Cheng et al., 2019;Pershing et al., 2015), which could consequently shift parts, or all, of their home range outside of protected areas. ...
... To accomplish this, we sought to address the following five primary questions: (1) What is the preferred temperature range of the studied tiger shark population? (2) What is the influence of temperature on tiger shark space use relative to other environmental factors known to affect their movements (i.e., chlorophyll a and ocean depth; e.g., Calich et al., 2018)? (3) Does the distributional range of tiger sharks extend farther poleward in response to warming seas? ...
... While the focus of this investigation was to assess how ocean warming may effect tiger shark space use and migrations, previous research in the region has revealed that in addition to seasurface temperature (SST), both chlorophyll-a concentration (ChlA) and ocean depth can influence tiger shark space use (Calich et al., 2018, Queiroz et al., 2016. Therefore, here we evaluated the degree to which these three variables influenced the probability of tiger shark spatial occurrence within each season using a population-level resource selection function analysis (RSF; Manly et al., 2007). ...
Given climate change threats to ecosystems, it is critical to understand the responses of species to warming. This is especially important in the case of apex predators since they exhibit relatively high extinction risk, and changes to their distribution could impact predator–prey interactions that can initiate trophic cascades. Here we used a combined analysis of animal tracking, remotely sensed environmental data, habitat modeling, and capture data to evaluate the effects of climate variability and change on the distributional range and migratory phenology of an ectothermic apex predator, the tiger shark (Galeocerdo cuvier). Tiger sharks satellite tracked in the western North Atlantic between 2010 and 2019 revealed significant annual variability in the geographic extent and timing of their migrations to northern latitudes from ocean warming. Specifically, tiger shark migrations have extended farther poleward and arrival times to northern latitudes have occurred earlier in the year during periods with anomalously high sea-surface temperatures. A complementary analysis of nearly 40 years of tiger shark captures in the region revealed decadal-scale changes in the distribution and timing of shark captures in parallel with long-term ocean warming. Specifically, areas of highest catch densities have progressively increased poleward and catches have occurred earlier in the year off the North American shelf. During periods of anomalously high sea-surface temperatures, movements of tracked sharks shifted beyond spatial management zones that had been affording them protection from commercial fishing and bycatch. Taken together, these study results have implications for fisheries management, human–wildlife conflict, and ecosystem functioning.
... Multiple species of top predators coexist within the productive coastal regions of the northwest Atlantic Ocean and the Gulf of Mexico, including tiger Galeocerdo cuvier, great hammerhead Sphyrna mokarran and bull sharks Carcharhinus leucas (Graham et al. 2016, Calich et al. 2018, NOAA 2019. Within this region, studies focused on broadscale movement patterns have revealed that tiger sharks have a widespread distribution through coastal and pelagic environments (Lea et al. 2015, Ajemian et al. 2020, great hammerheads are predominantly a coastal species that are frequently observed along the shelf (Hammerschlag et al. 2011, Guttridge et al. 2017, and bull sharks show high site fidelity in coastal areas, exhibiting seasonal coastal migrations (Carlson et al. 2010, Graham et al. 2016, Guttridge et al. 2017, Calich et al. 2018, Rider et al. 2021. ...
... Multiple species of top predators coexist within the productive coastal regions of the northwest Atlantic Ocean and the Gulf of Mexico, including tiger Galeocerdo cuvier, great hammerhead Sphyrna mokarran and bull sharks Carcharhinus leucas (Graham et al. 2016, Calich et al. 2018, NOAA 2019. Within this region, studies focused on broadscale movement patterns have revealed that tiger sharks have a widespread distribution through coastal and pelagic environments (Lea et al. 2015, Ajemian et al. 2020, great hammerheads are predominantly a coastal species that are frequently observed along the shelf (Hammerschlag et al. 2011, Guttridge et al. 2017, and bull sharks show high site fidelity in coastal areas, exhibiting seasonal coastal migrations (Carlson et al. 2010, Graham et al. 2016, Guttridge et al. 2017, Calich et al. 2018, Rider et al. 2021. Despite occupying slightly different habitats all three species are apex predators, commonly foraging on a variety of teleosts and other elasmobranchs in the study area, albeit with some variation between species (Snelson et al. 1984, Aines et al. 2018, Gallagher and Klimley 2018. ...
... Our results show that these species have well-established, complementary movement strategies that may enable these sympatric predators to co-exist. Furthermore, the co-existence of these species is currently supported by the fact that this is a highly productive region that benefits from multiple spatial protections (Graham et al. 2016, Calich et al. 2018, including the Bahamas Shark Sanctuary and a variety of gear restricted areas within US federal waters (e.g. NOAA 2019). ...
Animals follow specific movement patterns and search strategies to maximize encounters with essential resources (e.g. prey, favourable habitat) while minimizing exposures to suboptimal conditions (e.g. competitors, predators). While describing spatiotemporal patterns in animal movement from tracking data is common, understanding the associated search strategies employed continues to be a key challenge in ecology. Moreover, studies in marine ecology commonly focus on singular aspects of species' movements, however using multiple analytical approaches can further enable researchers to identify ecological phenomena and resolve fundamental ecological questions relating to movement. Here, we used a set of statistical physics-based methods to analyze satellite tracking data from three co-occurring apex predators (tiger, great hammerhead and bull sharks) that predominantly inhabit productive coastal regions of the northwest Atlantic Ocean and Gulf of Mexico. We analyzed data from 96 sharks and calculated a range of metrics, including each species' displacements, turning angles, dispersion, space-use and community-wide movement patterns to characterize each species' movements and identify potential search strategies. Our comprehensive approach revealed high interspecific variability in shark movement patterns and search strategies. Tiger sharks displayed near-random movements consistent with a Brownian strategy commonly associated with movements through resource-rich habitats. Great hammerheads showed a mixed-movement strategy including Brownian and resident-type movements, suggesting adaptation to widespread and localized high resource availability. Bull sharks followed a resident movement strategy with restricted movements indicating localized high resource availability. We hypothesize that the species-specific search strategies identified here may help foster the co-existence of these sympatric apex predators. Following this comprehensive approach provided novel insights into spatial ecology and assisted with identifying unique movement and search strategies. Similar future studies of animal movement will help characterize movement patterns and also enable the identification of search strategies to help elucidate the ecological drivers of movement and to understand species' responses to environmental change.
... Such studies have generally revealed preference for shallow (\ 20 m) and warm (26°C-33°C) coastal waters by mature and maturing C. leucas, largely restricted to inshore areas, with relatively low mobility. These findings have implications for conservation and management of adults as the core use areas of tagged individuals have rarely spanned multiple jurisdictions (Graham et al. 2016;Calich et al. 2018). However, tracking periods of these previous studies were relatively short (median tracking periods less than 3 months). ...
... C. leucas is euryhaline and inhabits low salinity environments such as rivers and estuaries, achievable via osmoregulation (Thorson 1972). The relationship between C. leucas movement and water temperature has been examined in previous studies, with mixed results (Ortega et al. 2009;Daly et al. 2014;Calich et al. 2018;Altobelli and Szedlmayer 2020). For example, one study found that juveniles' movements within a Florida estuary were significantly related to water temperature, with individuals occurring between surface temperatures of 27.0 and 37.3°C (mean = 30.4°C) ...
... It is possible that these comparatively high levels of chl a attract C. leucas due to increased fish abundance as a result of higher productivity. Our findings seemingly contrast with those of a recent study which found that chl a concentrations contributed the least to C. leucas habitat suitability models (Calich et al. 2018). However, this past study utilized chl a values averaged over longer periods (seasonal and year-round) in their models, which may have weakened the signal of shortterm variability in chl a that we detected in the present study (using daily and monthly mean values). ...
Understanding the movement ecology of marine species is important for conservation management and monitoring their responses to environmental change. In this study, adult and subadult bull sharks (Carcharhinus leucas; n = 16) were acoustically tagged in Biscayne Bay, Florida (USA), where they were tracked locally via an array of 40 passive acoustic receivers, as well as regionally via cooperative acoustic telemetry networks, with individuals tracked up to 4.5 years. Detection data were used to assess philopatry, regional connectivity, and environmental correlates of shark habitat use. Spatial range varied per individual; however, most individuals displayed high residency to Biscayne Bay, exhibiting strong philopa-tric behavior to the tagging area. A generalized linear mixed model revealed a seasonal pattern in habitat use, with mature females displaying high residency in Biscayne Bay during the colder dry season (November to February) and lower residencies during the warmer wet season (June to October). These seasonal patterns were supported by catch data from long-term fishery-independent shark surveys in the study area. During summer months when residencies of C. leucas declined in Biscayne Bay, their residencies increased in other regions (e.g., Florida Gulf Coast), demonstrative of seasonal migrations. Connectivity between areas of high use (Biscayne Bay and Florida Gulf Coast) was demonstrated by some individuals traveling between these areas. Results from generalized additive mixed models suggest that these movement patterns could be partially driven by seasonal changes in environmental variables as well as an individual's life stage, including reproductive status.
... Aspects of movement, demography, diet, habitat suitability, and reproductive ecology of this species have been studied at various sites and scales within the Western North Atlantic and Gulf of Mexico (e.g. Kohler et al., 1998;Driggers et al., 2008;Carlson et al., 2012;Hammerschlag et al., 2013;Leah et al., 2015;Vaudo et al., 2016;Sulikowski et al., 2016;Calich et al., 2018;Rooker et al., 2019). In addition, habitat use of this species in relation to spatial management zones in parts of the subtropical Western North Atlantic (Graham et al., 2016;Calich et al., 2018) and in relation to longline fisheries within international waters of the Mid-Atlantic Ocean (Queiroz et al., 2016(Queiroz et al., , 2019 has been investigated. ...
... Kohler et al., 1998;Driggers et al., 2008;Carlson et al., 2012;Hammerschlag et al., 2013;Leah et al., 2015;Vaudo et al., 2016;Sulikowski et al., 2016;Calich et al., 2018;Rooker et al., 2019). In addition, habitat use of this species in relation to spatial management zones in parts of the subtropical Western North Atlantic (Graham et al., 2016;Calich et al., 2018) and in relation to longline fisheries within international waters of the Mid-Atlantic Ocean (Queiroz et al., 2016(Queiroz et al., , 2019 has been investigated. While tiger sharks remain a significant component of US recreational and commercial shark fisheries (NOAA, 2018), their populations appear to be recovering in the Western North Atlantic from historical overfishing (Peterson et al., 2017). ...
... While tiger sharks remain a significant component of US recreational and commercial shark fisheries (NOAA, 2018), their populations appear to be recovering in the Western North Atlantic from historical overfishing (Peterson et al., 2017). This recovery has been hypothesized to be driven in part by opportunistic protection of tiger shark highly suitable habitat within large spatial zones restricting longline fishing (Calich et al., 2018). Taken together, the former studies on tiger sharks in the region provide data useful for informing and testing the results of spatially explicit models examining the effects of various spatial management strategies on the biomass of tiger sharks in the Western North Atlantic Ocean and Gulf of Mexico. ...
There has been debate in the literature over the use and success of spatial management zones (i.e. marine protected areas and time/area closures) as policy tools for commercially exploited sharks. The tiger shark (Galeocerdo cuvier) is a highly migratory predator found worldwide in warm temperate and tropical seas, which is caught in multiple US fisheries. We used a spatially explicit modelling approach to investigate the impact of varying spatial management options in the Western North Atlantic Ocean on tiger shark biomass, catch, and distribution, and impacts to other species in the ecosystem. Results suggest that under current management scenarios, tiger shark biomass will increase over time. Model outputs indicate that protecting additional habitats will have relatively minimal impacts on tiger shark biomass, as would increasing or decreasing protections in areas not highly suitable for tiger sharks. However, increasing spatial management protections in highly suitable habitats is predicted to have a positive effect on their biomass. Results also predict possible spill-over effects from current spatial protections. Our results provide insights for evaluating differing management strategies on tiger shark abundance patterns and suggest that management zones may be an effective conservation tool for highly migratory species if highly suitable habitat is protected.
... Similarly, tiger sharks (predominately female) tagged off south Florida and the northern Bahamas appear to exhibit associations with the Gulf Stream, presumably due to the high productivity, and thus food availability, in this current system [23,24]. By combining tracks from mostly adult female tiger sharks tagged in Florida and the Bahamas with remotely sensed environmental data, Calich et al. [25] predicted large areas of suitable habitat off the southeast United States, including the Gulf of Mexico (GoM). However, actual use of the predicted suitable habitat by tiger sharks remains unknown as does the importance of these habitats for males and juveniles. ...
... To date, satellite telemetry has been used to describe the movement patterns and habitat preferences of multiple GoM shark species including scalloped hammerhead (Sphyrna lewini) [29,30], dusky sharks (Carcharhinus obscurus) [31] shortfin makos (Isurus oxyrinchus) [32], and whale sharks (Rhincodon typus) [33,34]. While all life stages of tiger shark are known to occur in the GoM [11,25,28], detailed habitat use has never been quantified. This is striking as the GoM faces numerous anthropogenic stressors [35][36][37], complex tri-national management [38,39], and indications of size reductions in recreational landings for large sharks [40,41]. ...
... Such data can reveal the importance of these habitats over multiple years, and how residency within these systems changes with sex and size class. We suggest future studies incorporate technologies such as acoustic telemetry, which does not require animals to bear large external transmitters or to surface, and has already been applied to tiger sharks elsewhere [25,77,78]. Such data would also provide a glimpse into inter-bank and platform connectivity, site fidelity, and the role of tiger sharks in transporting nutrients across these various sites (i.e., allochthonous inputs). ...
The tiger shark (Galeocerdo cuvier) is globally distributed with established coastal and open-ocean movement patterns in many portions of its range. While all life stages of tiger sharks are known to occur in the Gulf of Mexico (GoM), variability in habitat use and movement patterns over ontogeny have never been quantified in this large marine ecosystem. To address this data gap we fitted 56 tiger sharks with Smart Position and Temperature transmitting tags between 2010 and 2018 and examined seasonal and spatial distribution patterns across the GoM. Additionally, we analyzed overlap of core habitats (i.e., 50% kernel density estimates) among individuals relative to large benthic features (oil and gas platforms, natural banks, bathymetric breaks). Our analyses revealed significant ontogenetic and seasonal differences in distribution patterns as well as across-shelf (i.e., regional) and sex-linked variability in movement rates. Presumably sub-adult and adult sharks achieved significantly higher movement rates and used off-shelf deeper habitats at greater proportions than juvenile sharks, particularly during the fall and winter seasons. Further, female maximum rate of movement was higher than males when accounting for size. Additionally, we found evidence of core regions encompassing the National Oceanographic and Atmospheric Administration designated Habitat Areas of Particular Concern (i.e., shelf-edge banks) during cooler months, particularly by females, as well as 2,504 oil and gas platforms. These data provide a baseline for future assessments of environmental impacts, such as climate variability or oil spills, on tiger shark movements and distribution in the region. Future research may benefit from combining alternative tracking tools, such as acoustic telemetry and genetic approaches, which can facilitate long-term assessment of the species’ movement dynamics and better elucidate the ecological significance of the core habitats identified here.
... Suitable habitat Calich et al. ( 2018 ) "Overlap between highly suitable habitats and longline gear management areas reveals vulnerable and protected regions for highly migratory sharks" ...
... We recommend accidents as a relevant node for future studies of marine vertebrate behaviour, and researchers can account for accident nodes by identifying the distribution and likelihood of sources of potential accidents at the scale of the Seascape or Community, e.g. fisheries overlap identified via vessel monitoring systems cross-checked to study species distributions (Calich et al., 2018 ;Kroodsma et al., 2018 ;Queiroz et al., 2019 ;White et al., 2019 ) (nodes: Anthropocene, storm frequency and intensity, and bodily harm, Figure 1 and Table 1 ). ...
Historic limitations have resulted in marine ecological studies usually overlooking some well-established concepts from behavioural ecology. This is likely because the methods available were easily overwhelmed by the scale of ecological processes and sampling resolution in the marine environment. Innovations in technology, data management, and statistical modelling now provide the capacity to fully embrace behavioural ecology concepts and study marine ecological interactions from a more holistic perspective. To facilitate this vision, we propose a novel perspective and workflow for marine ecology: the Seascape of Ecological Energy, or SEE-scapes. SEE-scapes contextualizes the accumulated knowledge from marine biology and behavioural ecology research and provides a guide for marine scientists interested in grounding their research in behavioural ecology’s first principles. SEE-scapes specifies relevant considerations for contemporary seascapes, with special attention to relationships between individuals and their conspecifics, competitors, predators, and the abiotic environment. It is formulated to account for how the unique features of marine vertebrates require revisions to standard, terrestrially focused methodological approaches, and offers solutions for how to sample and model the eco-evolutionary drivers of behaviour across the dynamic and hierarchical seascape. Simply put, SEE-scapes provides the guidance to translate a dynamic system and reveal opportunities for collaborative and integrative research.
... Ten additional studies investigated patterns between shark habitat use and fisheries operations, all of which showed some evidence of overlap between sharks and fishing effort (n = 10 species total; Queiroz et al., 2016;Calich et al., 2018;Queiroz et al., 2019;White et al., 2019a;Hutchinson et al., 2019;). Estimates of shark overlap with fisheries was highly dependent on species, ocean region, and season . ...
... Further, blue sharks overlapped with fishing effort across 79% of their space use in the North Atlantic, versus just 14% in the Eastern Pacific. Species vulnerability to fisheries interactions was determined using covariates such as level of fisheries management Calich et al., 2018;Rooker et al., 2019), logbook records and catch per unit effort (Lyons et al., 2013), onboard observer or fisher recapture data (Tolotti et al., 2015;Afonso and Hazin, 2014), gear characteristics (i.e., set depth; , and locational information supplied by GPS, vessel monitoring systems (VMS) and automatic identification systems (AIS). Co-application of these satellite technologies for vessel monitoring (i.e., VMS/AIS data; Queiroz et al., 2016White et al., 2019a) was absent from the previous review. ...
Satellite telemetry as a tool in marine ecological research continues to adapt and grow and has become increasingly popular in recent years to study shark species on a global scale. A review of satellite tag application to shark research was published in 2010, provided insight to the advancements in satellite shark tagging, as well as highlighting areas for improvement. In the years since, satellite technology has continued to advance, creating smaller, longer lasting, and more innovative tags, capable of expanding the field. Here we review satellite shark tagging studies to identify early successes and areas for rethinking moving forward. Triple the amount of shark satellite tagging studies have been conducted during the decade from 2010 to 2020 than ever before, tracking double the number of species previously tagged. Satellite telemetry has offered increased capacity to unravel ecological questions including predator and prey interactions, migration patterns, habitat use, in addition to monitoring species for global assessments. However, <17% of the total reviewed studies directly produced results with management or conservation outcomes. Telemetry studies with defined goals and objectives produced the most relevant findings for shark conservation, most often in tandem with secondary metrics such as fishing overlap or management regimes. To leverage the power of telemetry for the benefit of shark species, it remains imperative to continue improvements to tag function and maximize the outputs of tagging efforts including increasing data sharing capacity and standardization across the field, as well as spatial and species coverage. Ultimately, this review offers a status report of shark satellite tagging and the ways in which the field can continue to progress.
... These are highly migratory pelagic sharks and bony fishes (e.g., Alopias sp., C. falciformis, C. longimanus, C. leucas, Galeocerdo cuvier, I. oxyrinchus, P. glauca, Sphyrna sp., Thunnus albacares, Istiophorus platypterus, and Xiphias gladius). Nevertheless, it is essential to acknowledge that the distribution of these highly migratory pelagic shark and bony fishes (e.g., tunas and billfishes) overlaps with fishing fleets from other countries in both the Pacific and the Atlantic (Calich et al., 2018;White et al., 2019). This study focuses on evaluating the RV only for Mexican fisheries. ...
... Most of the elasmobranchs in this analysis resulted with moderate RV to fishing activities in Mexico. However, future analysis should consider that species may be subject to other sources of pressure (e.g., overlapping with fishing fleets from other countries, oil spills, climate change, and habitat loss) (Calich et al., 2018;Osgood et al., 2021;Yan et al., 2021;Romo-Curiel et al., 2022). Moreover, half of the evaluated elasmobranchs in this study belong to extinction risk categories of the Red List of Threatened Species of the International Union for Conservation of Nature (IUCN) of Critically Endangered, Endangered, and Vulnerable (Supplementary Table S3). ...
The main key drivers of vulnerability for marine species are anthropogenic stressors, ranging from pollution and fishing to climate change. The widely documented impacts of fishing activities on marine species, the growing concern about the population status of many marine species, and the increase in per capita consumption of marine products worldwide have led to the development of environmentally responsible fishing standards and initiatives to inform consumers about the health status of the species. In Mexico, fishing is a vital source of jobs and food security for many coastal communities, but the population status of many species of commercial importance has not been evaluated. Management efforts and fisheries certification procedures and standards to achieve the sustainability of many Mexican fisheries are hindered by a lack of biological and fishery data for many species. In this study, a risk assessment methodology for data-limited fisheries, a Productivity, and Susceptibility Analysis was used to estimate the relative vulnerability of marine invertebrates and fishes commercially important in Mexico to fishing. Ninety-eight invertebrates, 66 elasmobranchs, and 367 bony fish were analyzed. The vulnerability among the 531 evaluated species is high for 115 (22%), moderate for 113 (21%), and low for 303 (57%). The most vulnerable species are the Mexican geoduck (Panopea globosa) and the Black Sea Cucumber (Holothuria atra) for invertebrates, the Spiny butterfly ray (Gymnura altavela) among elasmobranches, and the Black-and-yellow rockfish (Sebastes chrysomelas) for bony fishes. This study provides a first screening of the many species potentially affected by fisheries, prioritizes marine species for future research and management efforts, identifies the main data gaps, and sets the baseline for future research efforts and management. Furthermore, the results could improve market-based approaches like eco-labeling initiatives and the Responsible Seafood
... Although our sample size does not permit any statistical comparisons between the two species, it is important to discuss these species together for purposes of regional management of pelagic, highly migratory species in the northern GOM. With the bigeye thresher (from our own study and others) consistently occupying comparatively shallower waters at night, and the scalloped hammerhead in similar depth ranges, both of these species are at risk of overlapping with nighttime operating tuna and swordfish commercial fisheries in the GOM [35,52,53]. In addition, there is a growing recreational and commercial industry of daytime deepdrop swordfish fisheries [54] that can heavily interact with bigeye threshers as they remain in deeper waters during the day. ...
... In addition, there is a growing recreational and commercial industry of daytime deepdrop swordfish fisheries [54] that can heavily interact with bigeye threshers as they remain in deeper waters during the day. These fisheries routinely alter gear characteristics, location, fishing depth, and time of day of deployment to maximize catch rates of their target species; however, these adjustments can then alter the composition (e.g., species, sex, maturity) and magnitude of bycatch [52,53]. Therefore, variable diel partitioning of the pelagic environment by these species of conservation concern (and others in the region) should be evaluated further for best management practices. ...
Understanding habitat use of elasmobranchs in pelagic environments is complicated due to the mobility of these large animals and their ability to move great distances in a three-dimensional environment. The Gulf of Mexico is a region where many highly migratory pelagic shark species occur, while in close proximity to coastal, anthropogenic activity including recreational and commercial fisheries. This study provides summary information on the vertical habitat use for a single male scalloped hammerhead and a single male bigeye thresher that were each caught and tagged with an archiving satellite tag. The scalloped hammerhead occupied shallow depths (<100 m) over the continental shelf during the 90 d deployment. The bigeye thresher exhibited strong patterns of diel vertical migrations by occupying depths below the thermocline (>350 m) during the day, then occupying shallower depths (50–100 m) during the night. By providing summary information, this note urges future research to provide scientific information on pelagic, highly migratory species for management efforts in the Gulf of Mexico region.
... Environmental variables (Table 1) were selected based on a literature review of environmental factors that correlate or that are known to influence the presence of each studied hammerhead shark (Heithaus et al., 2007;Ubeda et al., 2009;Froeschke et al., 2010;Belcher and Jennings, 2010;Ketchum et al., 2014a;Ward-Paige et al., 2015;Yates et al., 2015;Calich et al., 2018). Seasonal variation was not considered due to presence records limitations; thus, resulting maps are integrated static images that show no temporal variations (Guisan and Zimmermann, 2000;Ramírez-León et al., 2021). ...
... Finally, the absolute speed of the current related to the probability of great hammerhead's presence showed a peak at ∼0.1 m/s and from ∼0.4 m/s to ∼1.4 m/s in the present study. Calich et al. (2018) also found that great hammerhead's distribution increased between 0.06-1.4 m/s current speed. ...
Understanding the degree to which fishing operations overlap with the distribution of exploited populations is essential for population assessments and in the formulation of management measures. Here we used ecological niche models to estimate hammerhead sharks’ potential distribution that allowed the first assessment of their overlap with small-scale fishing operations in the southern Gulf of Mexico (GOM). The models were better than random models, with bathymetry as the most important predictor variable for bonnethead shark and average Chl-a for scalloped and great hammerheads. Shallow and intermediate waters of the GOM are of high environmental suitability for bonnethead shark and great hammerhead, and intermediate and deep waters within the continental shelf are more suitable for scalloped hammerhead. The spatial distribution of the small-scale fleet that operates on the western Yucatán Peninsula, southern GOM, had a high overlap with the estimated high environmental suitability of both bonnethead and great hammerhead sharks. We highlight the bonnethead shark, since its coastal habitat preference spans all ontogenetic stages, thus making it highly vulnerable to coastal anthropogenic impacts, including several small-scale fisheries.
... When combined with environmental data and spatial modeling techniques, telemetry data can be used to predict the distribution of highly migratory species at large scales (Block et al. 2011;Curtis et al. 2014). This can be useful for applications such as identifying areas of potential fishery interactions (Haulsee et al. 2018), assessing the use of closed and protected areas (Calich et al. 2018), and predicting the effects of large-scale environmental changes (Hazen et al. 2012). Passive acoustic telemetry, which entails the deployment of ultrasonic tags that are then detected by acoustic receivers, has traditionally been used to monitor marine animals in particular habitat areas or locations along migratory routes, but the advent of collaborative acoustic telemetry networks has enabled continental-scale spatial tracking, which was previously only possible through satellite-based telemetry (Donaldson et al. 2014;Udyawer et al. 2018). ...
... Extracted environmental variables were sea surface temperature (SST;°C) and chlorophyll-a concentration (Chl-a; mg/m 3 ), which were observed by the National Aeronautics and Space Administration (NASA) Moderate Resolution Imaging Spectroradiometer's Aqua sensor (Savtchenko et al. 2004); sea surface salinity (Sal; psu), which was recorded by the NASA Jet Propulsion Laboratory's Soil Moisture Active Passive satellite (Fore et al. 2016); and depth (m), which was available from the ETOPO1 Global Relief Model (Amante and Eakins 2009). These variables were chosen based on environmental associations that have been found to define habitat for highly migratory coastal species (Block et al. 2011;Curtis et al. 2014;Calich et al. 2018;Haulsee et al. 2018). Extracted data applied to each receiver location and date were mean values taken from within a radius of 0.01 decimal degrees (dd;~0.88-1.14 ...
Highly mobile species can be challenging for fisheries management and conservation due to large home ranges combined with dependence on discrete habitat areas where they can be easily targeted or vulnerable to anthropogenic disturbances. Management of the Dusky Shark Carcharhinus obscurus in the northwest Atlantic Ocean has been particularly challenging due to the species' inherent vulnerability to overfishing and poorly understood habitat associations. To better understand habitat associations and seasonal distributions, we combined telemetry and remotely sensed environmental data to spatially model juvenile Dusky Shark presence probability in the northwest Atlantic Ocean. To accomplish this, 22 juvenile Dusky Sharks (107-220 cm TL) that were tagged with acoustic transmitters at different locations within the U.S. Middle Atlantic Bight region were tracked through networked arrays of acoustic receivers. Tag detections were summarized as daily presence records, and data describing environmental conditions, including depth, chlorophyll-a concentration, salinity, and sea surface temperature, were extracted at detection locations. These data were used in boosted regression tree models to predict juvenile Dusky Shark presence probability based on environmental parameters during fall 2017 and summer 2018. Telemetry observations and modeled presence probability showed consistent associations with temperatures between 16°C and 26°C and chlorophyll-a concentrations between 2 and 7 mg/m 3 , which were associated with seasonal migration timing and monthly spatial distributions.
... Similarly, the fishing location of the catch landed in Lekok fishing port is in Madura Strait, which is close to the landing site. This study is critically important to determine spatial management strategies for those fisheries, especially for highly migratory species (Calich et al. 2018). ...
Wiadnya DGR, Harlyan LI, Rahman MA, Mustikarani SMI, Nadhiroh ENS, Taufani WT. 2023. Stock status and supporting species of anchovy fisheries in the northern of East Java, Indonesia. Biodiversitas 24: 4775-4782. Anchovy, a commercial fish with high demand in local and international markets, was selected as the Unit of Assessment (UoA) of the Fisheries Improvement Project (FIP) based on the priority fisheries consultation process under the Marine Stewardship Council certification in Indonesia. One of the criteria is the availability of stock status and information about supporting species. This research was conducted from January to May 2022 at Lekok Fishing Port, Pasuruan, and Karangagung Fishing Port, Tuban, using primary data collection methods, including a fishery survey to obtain data species composition data and fishing coordinates. The secondary data were the catch-effort data from 2013 to 2021 collected from both fishing ports. Data analysis was carried out by the surplus production models, Schaefer and Fox model, to determine the total allowable catch (TAC) and the exploitation rates of anchovy fisheries. The participatory mapping method was carried out to obtain data on the distribution of fishing grounds and catch composition. The exploitation rate of anchovy (Stolephorus commersonnii) and large anchovy (Encrasicholina punctifer) landed in the Lekok fishing port was 76% and 75% (moderate), respectively. In this situation, fishing efforts can still be increased, as TAC value for anchovy fisheries' sustainability. On the other hand, the exploitation rate of anchovy in the northern waters of Tuban is 105% (over-exploited), which is necessary to reduce fishing efforts for its sustainability. The classification of supporting species resulted in 19 identified species in the Lekok fishing port, covering three target species: two endangered threatened and protected (ETP) species, two main primary species, six minor primary species, one major secondary species, and five minor secondary species. While in Karangagung fishing port, eight species were identified, consisting of 1 major primary species, five minor primary species, and two minor secondary species. The supporting species' information is required to complete FIP Anchovy fisheries.
... Relationships between shark distribution and environmental factors such as dissolved oxygen, temperature, salinity and depth are well studied (e.g. Calich et al., 2018;Roskar et al., 2021;Drymon et al., 2020). While temperature is known to impact movement patterns and relative abundance of coastal sharks, our results only found significant temperature effects on abundance patterns of one species (C. ...
Given population declines of many shark species, coupled with increasing conservation efforts and recoveries, there is a need for baseline assessments and continued monitoring of shark populations to support management. The waters of South Florida, USA, are used by a diverse array of sharks that occur among a mosaic of habitats and management zones. Here we conducted standardized drumline surveys from Miami through the middle Florida Keys to examine spatial, seasonal and environmental patterns in shark occurrence, catch per unit effort, composition, and demographic structure. Between 2009 and 2021, a total of 21,755 drumlines were deployed, capturing 3398 sharks, comprising fifteen species. Ginglymostoma cirratum, (n = 1335), Carcharhinus limbatus, (n = 650), Negaprion brevirostris, (n = 314), C. leucas, (n = 253), and Sphyrna mokarran, (n = 238) were the most common species encountered. Overall, the largest shark surveyed was a 450 cm S. mokarran and the smallest shark was a 50 cm Rhizoprionodon terraenovae. At the assemblage level, relative abundance among regions and seasons were generally similar; however clear species-specific patterns of abundance, size structure, and sex-composition were detected by season, region, habitat, and management zones. Of the physical conditions evaluated, habitat type and depth emerged as the most influential parameters affecting abundances and sizes of species captured. While few species exhibited significant differences in catches by management zone, areas with the most restrictive fisheries regulations generally supported higher abundances for which differences were detected. These data serve as a baseline for future monitoring of shark populations in South Florida and assessing their response to environmental change.
... Satellite transmitters have successfully been used to track movements of pelagic sharks across ocean basins and has become a common tool for researchers (Hammerschlag et al., 2011;Hussey et al., 2015). Moreover, this technology has been widely used to monitor habitat use patterns (Hussey et al., 2015), as well as address inter-disciplinary ecological and resource management questions involving foraging ecology (Papastamatiou et al., 2010;Hammerschlag et al., 2011;Jaine et al., 2014), migratory behavior (Lea et al., 2015;Doherty et al., 2017a;Skomal et al., 2017) and overlap in species distribution and fishery exploitation areas (Graham et al., 2016;Queiroz et al., 2016;Calich et al., 2018). ...
In the northern Gulf of Mexico (GOM), whale sharks ( Rhincodon typus ) form large aggregations at continental shelf-edge banks during summer; however, knowledge of movements once they leave aggregation sites is limited. Here we report on the seasonal occurrence of whale sharks in the northern GOM based on over 800 whale shark sightings from 1989 to 2016, as well as the movements of 42 whale sharks tagged with satellite-linked and popup satellite archival transmitting tags from 2008 to 2015. Sightings data were most numerous during summer and fall often with aggregations of individuals reported along the continental shelf break. Most sharks (66%) were tagged during this time at Ewing Bank, a known aggregation site off the coast of Louisiana. Whale shark track duration ranged from three to 366 days and all tagged individuals, which ranged from 4.5 to 12.0 m in total length, remained within the GOM. Sightings data revealed that whale sharks occurred primarily in continental shelf and shelf-edge waters (81%) whereas tag data revealed the sharks primarily inhabited continental slope and open ocean waters (91%) of the GOM. Much of their time spent in open ocean waters was associated with the edge of the Loop Current and associated mesoscale eddies. During cooler months, there was a net movement southward, corresponding with the time of reduced sighting reports. Several sharks migrated to the southwest GOM during fall and winter, suggesting this region could be important overwintering habitat and possibly represents another seasonal aggregation site. The three long-term tracked whale sharks exhibited interannual site fidelity, returning one year later to the vicinity where they were originally tagged. The increased habitat use of north central GOM waters by whale sharks as summer foraging grounds and potential interannual site fidelity to Ewing Bank demonstrate the importance of this region for this species.
... Not surprisingly, MKDE analysis identified the highest space use in and around Pass a Loutre Wildlife Management Area, a region characterized by frequent freshwater discharge. These highly eutrophic freshwater pulses reduce dissolved oxygen (reviewed in Rabalais et al., 2014), which creates an inhospitable environment for predators that lack the tarpon's air-breathing organ (Babcock, 1951) and may reduce competition for shared prey resources, as well as provide refuge from regionally-abundant tarpon predators like bull sharks (Carcharhinus leucas) (Blackburn, Neer, & Thompson, 2007;Calich, Estevanez, & Hammerschlag, 2018). Future investigations are needed to confirm the importance of the local prey assemblage to tarpon feeding ecology. ...
Abstract Atlantic tarpon (Megalops atlanticus, hereafter tarpon) are facing a multitude of stressors and are considered Vulnerable by the IUCN; however, significant gaps remain in our understanding of tarpon space use and movement. From 2018 to 2019, citizen scientists facilitated tagging of 23 tarpon with SPOT tags to examine space use and movement across the northern Gulf of Mexico. Movement‐based kernel densities were used to estimate simplified biased random bridge‐based utilization distributions and a joint move persistence model was used to estimate a behavioral index for each fish. Tarpon showed consistent east–west movement from the Alabama/Florida border to Louisiana, and utilization distributions were highest in the Mississippi River Delta. Move persistence was highest in Alabama and Mississippi and lowest in Louisiana. Our examination of tarpon space use and movement indicates that Louisiana is a critical, yet understudied, part of their range.
... PSAT deployments Sharks in Miami were caught as part of an ongoing survey using methods described in Calich et al. [40], then briefly restrained for tagging and measurement. Sharks in Maryland were caught using rod and reel before tagging, measurement, and release. ...
A growing number of studies are using accelerometers to examine activity level patterns in aquatic animals. However, given the amount of data generated from accelerometers, most of these studies use loggers that archive acceleration data, thus requiring physical recovery of the loggers or acoustic transmission from within a receiver array to obtain the data. These limitations have restricted the duration of tracking (ranging from hours to days) and/or type of species studied (e.g., relatively sessile species or those returning to predictable areas). To address these logistical challenges, we present and test a satellite-transmitted metric for the remote monitoring of changes in activity, measured via a pop-off satellite archival tag (PSAT) with an integrated accelerometer. Along with depth, temperature, and irradiance for geolocation, the PSAT transmits activity data as a time-series (ATS) with a user-programmable resolution. ATS is a count of high-activity events, relative to overall activity/mobility during a summary period. An algorithm is used to identify the high-activity events from accelerometer data and reports the data as a count per time-series interval. Summary statistics describing the data used to identify high-activity events accompany the activity time-series. In this study, we first tested the ATS activity metric through simulating PSAT output from accelerometer data logger archives, comparing ATS to vectorial dynamic body acceleration. Next, we deployed PSATs with ATS under captive conditions with cobia (Rachycentron canadum). Lastly, we deployed seven pop-off satellite archival tags (PSATs) able to collect and transmit ATS in the wild on adult sandbar sharks (Carcharhinus plumbeus). In the captive trials, we identified both resting and non-resting behavior for species and used logistic regression to compare ATS values with observed activity levels. In captive cobia, ATS was a significant predictor of observed activity levels. For 30-day wild deployments on sandbar sharks, satellites received 57.4–73.2% of the transmitted activity data. Of these ATS datapoints, between 21.9 and 41.2% of records had a concurrent set of temperature, depth, and light measurements. These results suggest that ATS is a practical metric for remotely monitoring and transmitting relative high-activity data in large-bodied aquatic species with variable activity levels, under changing environmental conditions, and across broad spatiotemporal scales.
... As telemetry networks increasingly enable data collection at large spatial scales, the availability of large-scale remote sensing data from satellites enables those telemetry positions to be matched with physical environmental data. This in turn allows telemetry data to be used in habitat modeling at a variety of spatial scales (Braccini and Taylor 2016;Breece et al. 2016;Calich et al. 2018;Haulsee et al. 2018). Bangley et al. (2020) used this approach to identify seasonal distributions and areas of potentially important habitat for Dusky Sharks in the northwest Atlantic Ocean. ...
Acoustic telemetry, in which transmitters projecting ultrasonic signals carrying unique identification codes are deployed on marine and aquatic animals and detected and logged by acoustic receivers, is becoming a common tool in fisheries science. Collaboration among researchers using this technology has led to the development of telemetry networks that are capable of detecting transmitters at coastwide and even continental scales through the combined coverage of all members' receivers. Two grassroots telemetry networks in the northwest Atlantic and Caribbean, the Atlantic Cooperative Telemetry (ACT) Network and the FACT Network, began as small-scale efforts among neighboring researchers and have expanded to include shared databases of tagged animals along entire coastlines. A third telemetry network, the Ocean Tracking Network (OTN), has brought additional capacity to the ACT and FACT networks and has provided a focus for telemetry activities in Canadian waters. It has also improved the power and efficiency of telemetry research globally through collaborative, standardized methods for storing, sharing, and processing data. When used in combination with other data collected by traditional fishery research methods and emerging technologies , such as remote sensing and autonomous vehicles, data collected through acoustic telemetry networks can address fundamental but previously unanswered questions about key habitat areas and data-poor species and can yield new insights into the ecology of species that are thought to be well known. Here, we provide an overview of acoustic telemetry networks, including a history of the ACT Network, FACT Network, and OTN and a review of recent and current research that has been made possible through the connections enabled by these networks.
Human use of oceans has dramatically increased in the 21st century. Sea turtles are vulnerable to anthropogenic stressors in the marine environment because of lengthy migrations between foraging and breeding sites, often along coastal migration corridors. Little is known about how movement and threat interact specifically for male sea turtles. To better understand male sea turtle movement and the threats they encounter, we satellite-tagged 40 adult male sea turtles of four different species. We calculated movement patterns using state-space modeling (SSM), and quantified threats in seven unique categories; shipping, fishing, light pollution, oil rigs, proximity to coast, marine protected area (MPA) status, and location within or outside of the U.S. Exclusive Economic Zone (EEZ). We found significantly higher threat severity in northern and southern latitudes for green turtles (Chelonia mydas) and Kemp’s ridleys (Lepidochelys kempii) in our study area. Those threats were pervasive, with only 35.9% of SSM points encountering no high threat exposure, of which 47% belong to just two individuals. Kemp’s ridleys were most exposed to high threats among tested species. Lastly, turtles within MPA boundaries face significantly lower threat exposure, indicating MPAs could be a useful conservation tool.
The bull shark (Carcharhinus leucas Valenciennes, 1839) is a large, primarily coastally distributed shark famous for its ability to penetrate far into freshwater bodies in tropical, subtropical, and warm-temperate climates. It is a cosmopolitan species with a geographical range that includes the coastlines of all major ocean basins (Atlantic Ocean, Indian Ocean, Pacific Ocean). As a consequence, freshwater occurrences of C. leucas are possible everywhere inside its geographic range. Carcharhinus leucas is a fully euryhaline, amphidromous species and possibly the widest-ranging of all freshwater tolerating elasmobranchs. This species is found not only in river systems with sea access that are not interrupted by human impediments but in hypersaline lakes as well. Rivers and estuaries are believed to be important nursery grounds for C. leucas, as suggested by observations of pregnant females in estuaries and neonates with umbilical scars in rivers and river mouths. Due to the physical capability of this species to enter riverine systems, the documentation of its occurrence in fresh and brackish water is essential for future conservation plans, fishery inspections, and scientific studies that focus on the link between low salinity habitats, shark nurseries, and feeding areas. The author’s review of the available literature on C. leucas revealed the absence of a comprehensive overview of fresh and brackish water localities (rivers and associated lakes, estuaries) with C. leucas
records. The purpose of this literature review is to provide a global list of rivers, river systems, lakes, estuaries, and lagoons with records and reports of this species, including a link to the used references as a base for regional, national, and international conservation strategies. Therefore, the objective of this work is to present lists of fresh and brackish water habitats with records of C. leucas as the result of an extensive literature review and analysis of databases. This survey also took into account estuaries and lagoons, regarding their function as important nursery grounds for C. leucas. The analysis of references included is not only from the scientific literature, but also includes semi-scientific references and the common press if reliable. The result of 415 global fresh and brackish water localities with evidence of C. leucas highlights the importance of these habitats for the reproduction of this species. Moreover, gaps in available distribution maps are critically discussed as well as interpretations and conclusions made regarding possible reasons for the distribution range of C. leucas, which can be interpreted as the result of geographic circumstances, but also as a result of the current state of knowledge about the distribution of this species. The results of the examination of available references were used to build a reliable and updated distribution map for C. leucas, which is also presented here.
For many years, tremendous effort has been dedicated to developing new industrial tuna fisheries, while their adverse impacts on threatened marine species have received relatively little attention. In tuna fisheries, bycatch is the major anthropogenic threat to marine megafauna in general, particularly sharks. Research on the development of gear technology for bycatch reduction and potential mitigation measures helped tuna Regional Fisheries Management Organizations adopt bycatch reduction management measures. After reviewing past research on the development of mitigation measures for pelagic longline and tropical purse seine fisheries based on pelagic species' behaviours, we describe promising new approaches integrating recent technological breakthroughs. New innovations include autonomous underwater vehicles carrying cameras along with miniaturized sensors, aerial drones, computer simulation of fishing gear geometry, environmental DNA assays, computer visualizations and deep learning. The successful application of such tools and methods promises to improve our understanding of factors that influence capture, escape and stress of caught species. Moreover, results emerging from recent ethological research explaining the power of social connection and learning in the “fish world” such as social learning from congeners, habituation to deterrents, and how past fishery interactions affect responses to fishing gear should be taken into account when developing technical mitigation measures.
Animal‐borne telemetry has revolutionized our ability to study animal movement, species physiology, demography and social structures, changing environments and the threats that animals are experiencing. While there will always be a need for basic ecological research and discovery, the current conservation crisis demands we look more pragmatically at the data required to make informed management decisions.
Here, we define a framework that distinguishes how research using animal telemetry devices can influence conservation. We then discuss two critical questions which aim to directly connect telemetry‐derived data to applied conservation decision‐making: (i) Would my choice of action change if I had more data? (ii) Is the expected gain worth the money and time required to collect more data?
Policy implications . To answer questions about integrating telemetry‐derived data with applied conservation, we suggest the use of value of information analysis to quantitatively assess the return‐on‐investment of animal telemetry‐derived data for conservation decision‐making.
Commercial tunas and billfishes (swordfish, marlins and sailfish) provide considerable catches and income in both developed and developing countries. These stocks vary in status from lightly exploited to rebuilding to severely depleted. Previous studies suggested that this variability could result from differences in life-history characteristics and economic incentives, but differences in exploitation histories and management measures also have a strong effect on current stock status. Although the status (biomass and fishing mortality rate) of major tuna and billfish stocks is well documented, the effect of these diverse factors on current stock status and the effect of management measures in rebuilding stocks have not been analysed at the global level. Here, we show that, particularly for tunas, stocks were more depleted if they had high commercial value, were long-lived species, had small pre-fishing biomass and were subject to intense fishing pressure for a long time. In addition, implementing and enforcing total allowable catches (TACs) had the strongest positive influence on rebuilding overfished tuna and billfish stocks. Other control rules such as minimum size regulations or seasonal closures were also important in reducing fishing pressure, but stocks under TAC implementations showed the fastest increase of biomass. Lessons learned from this study can be applied in managing large industrial fisheries around the world. In particular, tuna regional fisheries management organizations should consider the relative effectiveness of management measures observed in this study for rebuilding depleted large pelagic stocks.
Study aim and location: Many populations of highly mobile marine fishes, including large sharks, are experiencing declines. The benefits of spatial management zones, such as marine protected areas (MPAs), for such animals are unclear. To help fill this knowledge gap, we examined core habitat use areas (CHUAs) for bull (Carcharhinus leucas), great hammerhead (Sphyrna mokarran) and tiger sharks (Galeocerdo cuvier) in relation to specific MPAs and exclusive economic zones (EEZs) in the western North Atlantic Ocean.
Methods: Bull, great hammerhead and tiger sharks (N = 86 total) were satellite tagged and tracked in southern Florida and the northern Bahamas between 2010 and 2013. Filtered and regularized positions from Argos locations of tag transmissions were used to generate CHUAs for these sharks. Overlaps of CHUAs with regional protected areas and exclusive economic management zones were quantified to determine the proportion of each tracked shark’s CHUA under spatial protection from exploitation.
Results: A total of 0%, 17.9% and 34.7% of the regional CHUAs for tracked bull, great hammerhead and tiger sharks, respectively, were fully protected from exploitation in the study area.
Main conclusions: Expansion of protected areas to include U.S. territorial waters would effectively protect 100% of the CHUAs for all tracked sharks in the study area. This finding is particularly significant for great hammerhead sharks, which are currently overfished, vulnerable to bycatch mortality and are the focus of strident regional conservation efforts. These findings also provide a
means to inform decision makers and marine conservation planning efforts as to the types of management actions available and potential efficacy of spatial protections for these marine predators.
Significance
Shark populations are declining worldwide because of overexploitation by fisheries with unknown consequences for ecosystems. Although the harvest of oceanic sharks remains largely unregulated, knowing precisely where they interact with fishing vessels will better aid their conservation. We satellite track six species of shark and two entire longline fishing vessel fleets across the North Atlantic over multiple years. Sharks actively select and aggregate in space-use “hotspots” characterized by thermal fronts and high productivity. However, longline fishing vessels also target these habitats and efficiently track shark movements seasonally, leading to an 80% spatial overlap. Areas of highest overlap between sharks and fishing vessels show persistence between years, suggesting current hotspots are at risk, and arguing for introduction of international catch limits.
Any attempt to describe the spatial ecology of sharks and rays should consider the drivers responsible for movement. Research has shown fluctuations in the environment (abiotic factors) can trigger movement and changes in behaviour and habitat use for many elasmobranch species. Most studies to date have selectively focused on a small number of abiotic factors (i.e. temperature, salinity); however, other factors such as dissolved oxygen, tide, photoperiod, barometric pressure and pH have also been documented to act as drivers of movement in shark and ray species. Although usually examined individually, abiotic factors rarely act in isolation and often differ in their level of influence between species, sex, ontogenetic stage, season and geographic location. This paper reviews the role of abiotic factors as a driver of movement and changes in behaviour and habitat use in elasmobranchs. In the context of a changing climate, insight into how sharks and rays may respond to fluctuating environmental conditions projected under future scenarios is required.
Migratory marine species (MMS) include many of the world's most charismatic organisms such as marine mammals, seabirds, turtles, sharks, and tuna. Many are now among the most threatened due to the diverse range of pressures they encounter during their extensive movements. This paper shows that 21% of MMS are classified as threatened (i.e. categorized as Critically Endangered, Endangered or Vulnerable). Sea turtles are the most threatened group (85%), followed by seabirds (27%), cartilaginous fish (26%), marine mammals (15%) and bony fish (11%). Taken together 48% of MMS are threatened, Near Threatened or Data Deficient.
As well as being threatened they share in common being wide-ranging animals, travelling through the waters of multiple nations as well as in Areas Beyond National Jurisdiction (ABNJ) during different times of the year. This makes their conservation a challenge, requiring coordinated action by many nations, international organizations, Multilateral Environmental Agreements (MEAs) and other stakeholders if their populations are to recover to healthy levels and be safeguarded into the future.
Even though they are wide-ranging, long-term studies reveal considerable site fidelity and well-defined habitats for many species and areas. These sites are prime candidates for enhanced management such as via Marine Protect Area (MPA) designations. However, existing management frameworks do not yet contribute sufficiently to MMS conservation, MPA networks need to be expanded to capture key areas, in many cases through the application of new dynamic management techniques such as time area closures.
Data on the distribution, abundance, behaviours and threats faced by many MMS are now available. These data should be used to inform the design of effective management regimes, such as MPAs, both within and beyond national jurisdictions. MEAs should ensure a full complement of MMS are included within species listings, and encourage further action to safeguard their populations.
Bycatch (the unintentional catch of non-target species or sizes) is consistently ranked as one of the greatest threats to marine fish populations; yet species-specific rates of bycatch survival are rarely considered in risk assessments. Regulations often require that bycatch of threatened species be released; but, if animals are already dead, their release serves no conservation purpose. We examined the survival of 12 shark species caught as bycatch in the US Atlantic pelagic longline fishery. Shark survival was evaluated in relation to fishery target (swordfish versus tuna) and four operational, environmental, and biological variables to evaluate the underlying mechanisms affecting mortality. Survival estimates ranged from 33% (night shark) to 97% (tiger shark) with seven of the 12 species being significantly affected by at least one variable. We placed our survival results within a framework that assessed each species' relative vulnerability by integrating survival estimates with reproductive potential and found that the bigeye thresher, dusky, night, and scalloped hammerhead shark exhibited the highest vulnerabilities to bycatch. We suggest that considering ecological and biological traits of species shows promise for designing effective conservation measures, whereas techniques that reduce fisheries interactions in the first place may be the best strategy for highly vulnerable species. © 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).
From 1994–2005 the Commercial Shark Fishery Observer Program (CSFOP) placed fishery observ-ers aboard US bottom longline vessels engaged in directed fishing for sharks in the region from New Jersey to Louisiana, USA. Observers routinely recorded species specific at-vessel mortality as related to enduring the stress of longline capture. Data for 5 species of sharks (sandbar Carcharhinus plumbeus, blacktip Carcharhinus limbatus, dusky Carcharhinus obscurus, tiger Galeocerdo cuvier, scalloped hammerhead Sphyrna lewini, and great hammer-head Sphyrna mokarran) were analyzed in this study. Multiple stepwise linear regressions indicate that age group, soak time and bottom water temperature can be used as predictors of at-vessel mortality and that size restrictions, size selective gear, restricting the soak time and time/area closures may be beneficial to fisheries targeting large coastal sharks. RESUMEN El Programa de Observación de la Pesquería Comercial de Tiburones sitúo observadores durante el periodo 1994–2005 en naves pesqueras dedicadas específicamente a la pesca con palangre de especies costeras grandes de tiburones en la región comprendida entre los estados de New Jersey y Lousiana en la costa estadoun-idense. Estos observadores tomaron datos sobre la habilidad de diferentes especies para sobrevivir el estrés de la captura con palangre. En este estudio analizamos datos de seis especies (Carcharhinus plumbeus o tiburón trozo, Carcharhinus limbatus o tiburón macuira, Carcharhinus obscurus o tiburón arenero, Galeocerdo cuvieri o tintorera tigre, Sphyrna lewini o cornuda común, y Sphyrna mokarran o cornuda gigante). El múltiplo el retroceso lineal pro-gresivo indican que el uso de restricciones por tamaño, tiempo en el agua, tipo de equipo y el cierre de pesquerías por área o por periodo pueden beneficiar el manejo de las pesquerías de tiburones costeros grandes.
Circle hooks have gained recent attention as a cost-effective bycatch mitigation tool in pelagic longline fisheries, particularly for marine turtles. Over the last few years, a growing number of studies have investigated the use of circle hooks and their effects on other species, including elasmobranchs. To elucidate the potential value of circle hook use as a tool for shark conservation and management in pelagic longline fisheries, we conducted a quantitative review of all available studies to date. We compiled 15 published and eight gray literature studies and where possible used random effects meta-analysis and analysis of covariance to test the effects of circle hooks on catchability and at-vessel mortality rates. Overall, results suggest that using circle hooks on pelagic longlines do not have a major effect on shark catch rates, but do reduce at-vessel mortality compared to J-hooks. Thus circle hooks should be seen as one potential tool to help reduce bycatch mortality of sharks in longline fisheries. However, the high level of heterogeneity found between studies highlights the need for shark-specific controlled experiments to provide more definitive results.
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.
The local distribution of basking sharks in the Bay of Fundy (BoF) is unknown despite frequent occurrences in the area from May to November. Defining this species' spatial habitat use is critical for accurately assessing its Special Concern conservation status in Atlantic Canada. We developed maximum entropy distribution models for the lower BoF and the northeast Gulf of Maine (GoM) to describe spatiotemporal variation in habitat use of basking sharks. Under the Maxent framework, we assessed model responses and distribution shifts in relation to known migratory behavior and local prey dynamics. We used 10 years (2002-2011) of basking shark surface sightings from July-October acquired during boat-based surveys in relation to chlorophyll-a concentration, sea surface temperature, bathymetric features, and distance to seafloor contours to assess habitat suitability. Maximum entropy estimations were selected based on AICc criterion and used to predict habitat utilizing three model-fitting routines as well as converted to binary suitable/non-suitable habitat using the maximum sensitivity and specificity threshold. All models predicted habitat better than random (AUC values >0.796). From July-September, a majority of habitat was in the BoF, in waters >100 m deep, and in the Grand Manan Basin. In October, a majority of the habitat shifted southward into the GoM and to areas >200 m deep. Model responses suggest that suitable habitat from July - October is dependent on a mix of distance to the 0, 100, 150, and 200 m contours but in some models on sea surface temperature (July) and chlorophyll-a (August and September). Our results reveal temporally dynamic habitat use of basking sharks within the BoF and GoM. The relative importance of predictor variables suggests that prey dynamics constrained the species distribution in the BoF. Also, suitable habitat shifted minimally from July-September providing opportunities to conserve the species during peak abundance in the region.
Whale shark Rhincodon typus is a globally distributed species, but there is a lack of
knowledge pertaining to their biology, seasonal occurrence, and distribution in the northern Gulf
of Mexico (NGOM). Understanding critical habitat for whale sharks is essential on both a regional
and global basis for proper management because of their large migratory range. The goal of the
present study was to describe the regional distribution of whale shark feeding aggregations in the
NGOM by exploiting a presence-only dataset collected as a part of a volunteer sighting survey.
Whale shark aggregations have been documented in large numbers in the NGOM since 2003, and
species distribution models provide a unique approach to analyzing these presence data. We used
maximum entropy and ecological niche factor analysis, 2 algorithms designed for predicting species
distribution based only on presence data, to analyze data for the summer period in 2008 and
2009. Cohen’s kappa (kappa) and the ‘area under the receiver operating characteristic curve’
(AUC) were used to evaluate model performance with an external testing dataset. Kappa values
ranged from 0.28 to 0.69, and AUC values ranged from 0.73 to 0.80, indicating that the predicted
distribution had a fair to substantial agreement with the testing data. Distance to continental shelf
edge, distance to adjacent petroleum platforms, and chlorophyll a were the variables most
strongly related to whale shark sightings, likely due to an association of these variables with high
food availability. Suitable habitat was predicted along the continental shelf edge, with the most
suitable habitat predicted south of the Mississippi River Delta. The spatial distribution of suitable
habitat is dynamic; therefore, a multi-year study is underway to better delineate temporal trends
in regional whale shark distribution and to identify consistent areas of high suitability. Presenceonly
habitat models are a powerful tool for delineating important regional habitat for a vulnerable,
highly migratory species.
Due to human activities, marine and terrestrial ecosystems face a future where disturbances are predicted to occur at a frequency and severity unprecedented in the recent past. Of particular concern is the ability of systems to recover where multiple stressors act simultaneously. We examine this issue in the context of a coral reef ecosystem where increases in stressors, such as fisheries, benthic degradation, cyclones and coral bleaching, are occurring at global scales. By utilizing long-term (decadal) monitoring programs, we examined the combined effects of chronic (removal of sharks) and pulse (cyclones, bleaching) disturbances on the trophic structure of coral reef fishes at two isolated atoll systems off the coast of northwest Australia. We provide evidence consistent with the hypothesis that the loss of sharks can have an impact that propagates down the food chain, potentially contributing to mesopredator release and altering the numbers of primary consumers. Simultaneously, we show how the effects of bottom-up processes of bleaching and cyclones appear to propagate up the food chain through herbivores, planktivores and corallivores, but do not affect carnivores. Because their presence may promote the abundance of herbivores, the removal of sharks by fishing has implications for both natural and anthropogenic disturbances involving the loss of corals, as herbivores are critical to the progress and outcome of coral recovery.
Recovery of overexploited marine populations has been slow, and most remain below target biomass levels. A key question is
whether this is due to insufficient reductions in harvest rates or the erosion of population resilience. Using a global meta-analysis
of overfished stocks, we find that resilience of those stocks subjected to moderate levels of overfishing is enhanced, not
compromised, offering the possibility of swift recovery. However, prolonged intense overexploitation, especially for collapsed
stocks, not only delays rebuilding but also substantially increases the uncertainty in recovery times, despite predictable
influences of fishing and life history. Timely and decisive reductions in harvest rates could mitigate this uncertainty. Instead,
current harvest and low biomass levels render recovery improbable for the majority of the world’s depleted stocks.
Recently, interest in species distribution modelling has increased following the development of new methods for the analysis of presence‐only data and the deployment of these methods in user‐friendly and powerful computer programs. However, reliable inference from these powerful tools requires that several assumptions be met, including the assumptions that observed presences are the consequence of random or representative sampling and that detectability during sampling does not vary with the covariates that determine occurrence probability.
Based on our interactions with researchers using these tools, we hypothesized that many presence‐only studies were ignoring important assumptions of presence‐only modelling. We tested this hypothesis by reviewing 108 articles published between 2008 and 2012 that used the MAXENT algorithm to analyse empirical (i.e. not simulated) data. We chose to focus on these articles because MAXENT has been the most popular algorithm in recent years for analysing presence‐only data.
Many articles (87%) were based on data that were likely to suffer from sample selection bias; however, methods to control for sample selection bias were rarely used. In addition, many analyses (36%) discarded absence information by analysing presence–absence data in a presence‐only framework, and few articles (14%) mentioned detection probability. We conclude that there are many misconceptions concerning the use of presence‐only models, including the misunderstanding that MAXENT , and other presence‐only methods, relieve users from the constraints of survey design.
In the process of our literature review, we became aware of other factors that raised concerns about the validity of study conclusions. In particular, we observed that 83% of articles studies focused exclusively on model output (i.e. maps) without providing readers with any means to critically examine modelled relationships and that MAXENT 's logistic output was frequently (54% of articles) and incorrectly interpreted as occurrence probability.
We conclude with a series of recommendations foremost that researchers analyse data in a presence–absence framework whenever possible, because fewer assumptions are required and inferences can be made about clearly defined parameters such as occurrence probability.
A limiting factor of satellite telemetry in the context of habitat ase by marine mammals is the low accuracy of the received positions. A novel statistical analysis to overcome the low accuracy was developed in the context of processing data on harbour seals phoca vitulina for the atlas of Danish mammals. Ten harbour seals were caught in the Danish Wadden Sea and tracked with satelite transmitters. The statistical analysis reversed the problem of positioning: Instead of attempting to correctly assign each individual position to a single grid cell, our approach considers the combined probability that at least one position originated in each grid cell. Thus, all satellite-derived positions, including positions of poor precision, can contribute to the evaluation. The method is an alternative to other methods describing spatial use, such as kernel home range, and constitutes a viable approach for inclusion of satellite-derived positional data into spatial modeling of animal distribution and habitat use.
Prediction of species’ distributions is central to diverse applications in ecology, evolution and conservation science. There is increasing electronic access to vast sets of occurrence records in museums and herbaria, yet little effective guidance on how best to use this information in the context of numerous approaches for modelling distributions. To meet this need, we compared 16 modelling methods over 226 species from 6 regions of the world, creating the most comprehensive set of model comparisons to date. We used presence-only data to fit models, and independent presence-absence data to evaluate the predictions. Along with well-established modelling methods such as generalised additive models and GARP and BIOCLIM, we explored methods that either have been developed recently or have rarely been applied to modelling species’ distributions. These include machine-learning methods and community models, both of which have features that may make them particularly well suited to noisy or sparse information, as is typical of species’ occurrence data. Presence-only data were effective for modelling species’ distributions for many species and regions. The novel methods consistently outperformed more established methods. The results of our analysis are promising for the use of data from museums and herbaria, especially as methods suited to the noise inherent in such data improve.
Until recently, large apex consumers were ubiquitous across the globe and had been for millions of years. The loss of these
animals may be humankind’s most pervasive influence on nature. Although such losses are widely viewed as an ethical and aesthetic
problem, recent research reveals extensive cascading effects of their disappearance in marine, terrestrial, and freshwater
ecosystems worldwide. This empirical work supports long-standing theory about the role of top-down forcing in ecosystems but
also highlights the unanticipated impacts of trophic cascades on processes as diverse as the dynamics of disease, wildfire,
carbon sequestration, invasive species, and biogeochemical cycles. These findings emphasize the urgent need for interdisciplinary
research to forecast the effects of trophic downgrading on process, function, and resilience in global ecosystems.
The first standardized, global assessment of these fishes, using Red List criteria, reveals threatened species needing protection.
Despite growing concerns about overexploitation of sharks, lack of accurate, species-specific harvest data often hampers quantitative stock assessment. In such cases, trade studies can provide insights into exploitation unavailable from traditional monitoring. We applied Bayesian statistical methods to trade data in combination with genetic identification to estimate by species, the annual number of globally traded shark fins, the most commercially valuable product from a group of species often unrecorded in harvest statistics. Our results provide the first fishery-independent estimate of the scale of shark catches worldwide and indicate that shark biomass in the fin trade is three to four times higher than shark catch figures reported in the only global data base. Comparison of our estimates to approximated stock assessment reference points for one of the most commonly traded species, blue shark, suggests that current trade volumes in numbers of sharks are close to or possibly exceeding the maximum sustainable yield levels.
The scalloped hammerhead Sphyrna lewini and the great hammerhead S. mokarran are typically caught as bycatch in a variety of fisheries and are listed as globally Endangered by the International Union for the Conservation of Nature. Due to very high at-vessel mortality for these species, research is needed on fishing methods to reduce mortality for longline-captured sharks. A series of fishing experiments were conducted employing hook timers and temperature–depth recorders on contracted commercial vessels fishing with bottom-longline gear to assess factors related to mortality. A total of 273 sets were deployed with 54 485 hook timers. Scalloped and great hammerheads had at-vessel mortality rates of 62.9% and 56.0%, respectively. Median hooking times for scalloped and great hammerheads were 3.5 h and 3.4 h, respectively, and 50% mortality was predicted at 3.5 h and 3.8 h. When these data are considered for potential management strategies to reduce the mortality of hammerhead sharks, a limitation on gear soak time would probably improve hammerhead shark survivorship. However, it may prove to be difficult for a fishery to remain economically viable if the soak time is limited to less than the median hooking time for the target species. Additional management options, such as time/area closures, may need to be explored to reduce bycatch mortality of scalloped and great hammerheads.
The MaxEnt software package is one of the most popular tools for species distribution and environmental niche modeling, with over 1000 published applications since 2006. Its popularity is likely for two reasons: 1) MaxEnt typically outperforms other methods based on predictive accuracy and 2) the software is particularly easy to use. MaxEnt users must make a number of decisions about how they should select their input data and choose from a wide variety of settings in the software package to build models from these data. The underlying basis for making these decisions is unclear in many studies, and default settings are apparently chosen, even though alternative settings are often more appropriate. In this paper, we provide a detailed explanation of how MaxEnt works and a prospectus on modeling options to enable users to make informed decisions when preparing data, choosing settings and interpreting output. We explain how the choice of background samples reflects prior assumptions, how nonlinear functions of environmental variables (features) are created and selected, how to account for environmentally biased sampling, the interpretation of the various types of model output and the challenges for model evaluation. We demonstrate MaxEnt’s calculations using both simplified simulated data and occurrence data from South Africa on species of the flowering plant family Proteaceae. Throughout, we show how MaxEnt’s outputs vary in response to different settings to highlight the need for making biologically motivated modeling decisions.
In many fisheries, some component of the catch is usually released. Quantifying the
effects of capture and release on fish survival is critical for determining which practices are sustainable,
particularly for threatened species. Using a standardized fishing technique, we studied
sublethal (blood physiology and reflex impairment assessment) and lethal (post-release mortality
with satellite tags) outcomes of fishing stress on 5 species of coastal sharks (great hammerhead,
bull, blacktip, lemon, and tiger). Species-specific differences were detected in whole blood
lactate, partial pressure of carbon dioxide, and pH values, with lactate emerging as the sole
parameter to be significantly affected by increasing hooking duration and shark size. Species-specific
differences in reflex impairment were also found; however, we did not detect any significant
relationships between reflex impairment and hooking duration. Taken together, we ranked each
species according to degree of stress response, from most to least disturbed, as follows: hammerhead
shark > blacktip shark > bull shark > lemon shark > tiger shark. Satellite tagging data
revealed that nearly 100% of all tracked tiger sharks reported for at least 4 wk after release, which
was significantly higher than bull (74.1%) and great hammerhead (53.6%) sharks. We discuss
which mechanisms may lead to species-specific differences in sensitivity to fishing and suggest
that observed variation in responses may be influenced by ecological and evolutionary phenomena.
Moreover, our results show that certain species (i.e. hammerhead sharks in this study) are
inherently vulnerable to capture stress and mortality resulting from fisheries interactions and
should receive additional attention in future conservation strategies.
We provide pilot data from a satellite-tracked great hammerhead shark Sphyrna mokarran in the Atlantic, representing the first such data on this species in the literature. The 250 cm shark was tagged off the coast of the middle-Florida Keys (USA) and transmitted for 62 d. During this time it migrated a minimum distance of ~1200 km northeast from the coast of Florida, into pelagic international waters of the Northwest Atlantic. When compared to the primary literature, this migration represented a northeasterly range extension for this species off the continental slope in the Atlantic. The significance of this range extension is discussed in terms of the vulnerability of S. mokarran to target and non-target fisheries.
This article presents a global overview of the efforts undertaken by coastal states, distant water fishing nations, and regional organizations to manage high seas fisheries following extension of jurisdiction and the 1982 United Nations Convention on the Law of the Sea. In particular, the article examines the management and conservation of those stocks defined under Article 63 of the convention as “straddling”; fish stocks, occurring both within areas of national jurisdiction and in the high seas area beyond and adjacent to the exclusive economic zone; and “highly migratory species,”; defined to include tuna and tuna‐like species, whose migration patterns cover vast expanses of ocean space. The inability of coastal and distant water fishing states to cooperate in the management and conservation of these resources has led to unsustainable fishing and collapse of many stocks. As a result the United Nations has convened an international Conference on Straddling Fish Stocks and Highly Migratory Fish Stocks.
Aim Predicting distribution patterns of whale sharks (Rhincodon typus, Smith 1828) in the open ocean remains elusive owing to few pelagic records. We developed multivariate distribution models of seasonally variant whale shark distributions derived from tuna purse-seine fishery data. We tested the hypotheses that whale sharks use a narrow temperature range, are more abundant in productive waters and select sites closer to continents than the open ocean.
Location Indian Ocean.
Methods We compared a 17-year time series of observations of whale sharks associated with tuna purse-seine sets with chlorophyll a concentration and sea surface temperature data extracted from satellite images. Different sets of pseudo-absences based on random distributions, distance to shark locations and tuna catch were generated to account for spatiotemporal variation in sampling effort and probability of detection. We applied generalized linear, spatial mixed-effects and Maximum Entropy models to predict seasonal variation in habitat suitability and produced maps of distribution.
Results The saturated generalized linear models including bathymetric slope, depth, distance to shore, the quadratic of mean sea surface temperature, sea surface temperature variance and chlorophyll a had the highest relative statistical support, with the highest percent deviance explained when using random pseudo-absences with fixed effect-only models and the tuna pseudo-absences with mixed-effects models (e.g. 58% and 26% in autumn, respectively). Maximum Entropy results suggested that whale sharks responded mainly to variation in depth, chlorophyll a and temperature in all seasons. Bathymetric slope had only a minor influence on the presence.
Main conclusions Whale shark habitat suitability in the Indian Ocean is mainly correlated with spatial variation in sea surface temperature. The relative influence of this predictor provides a basis for predicting habitat suitability in the open ocean, possibly giving insights into the migratory behaviour of the world’s largest fish. Our results also provide a baseline for temperature-dependent predictions of distributional changes in the future.
MaxEnt is a program for modelling species distributions from presence-only species records. This paper is written for ecologists and describes the MaxEnt model from a statistical perspective, making explicit links between the structure of the model, decisions required in producing a modelled distribution, and knowledge about the species and the data that might affect those decisions. To begin we discuss the characteristics of presence-only data, highlighting implications for modelling distributions. We particularly focus on the problems of sample bias and lack of information on species prevalence. The keystone of the paper is a new statistical explanation of MaxEnt which shows that the model minimizes the relative entropy between two probability densities (one estimated from the presence data and one, from the landscape) defined in covariate space. For many users, this viewpoint is likely to be a more accessible way to understand the model than previous ones that rely on machine learning concepts. We then step through a detailed explanation of MaxEnt describing key components (e.g. covariates and features, and definition of the landscape extent), the mechanics of model fitting (e.g. feature selection, constraints and regularization) and outputs. Using case studies for a Banksia species native to south-west Australia and a riverine fish, we fit models and interpret them, exploring why certain choices affect the result and what this means. The fish example illustrates use of the model with vector data for linear river segments rather than raster (gridded) data. Appropriate treatments for survey bias, unprojected data, locally restricted species, and predicting to environments outside the range of the training data are demonstrated, and new capabilities discussed. Online appendices include additional details of the model and the mathematical links between previous explanations and this one, example code and data, and further information on the case studies.
Accurate modeling of geographic distributions of species is crucial to various applications in ecology and conservation. The best performing techniques often require some parameter tuning, which may be prohibitively time-consuming to do separately for each species, or unreliable for small or biased datasets. Additionally, even with the abundance of good quality data, users interested in the application of species models need not have the statistical knowledge required for detailed tuning. In such cases, it is desirable to use ‘‘default settings’’, tuned and validated on diverse datasets. Maxent is a recently introduced modeling technique, achieving high predictive accuracy and enjoying several additional attractive properties. The performance of Maxent is influenced by a moderate number of parameters. The first contribution of this paper is the empirical tuning of these parameters. Since many datasets lack information about species absence, we present a tuning method that uses presence-only data. We evaluate our method on independently collected high-quality presenceabsence data. In addition to tuning, we introduce several concepts that improve the predictive accuracy and running time of Maxent. We introduce ‘‘hinge features’ ’ that model more complex relationships in the training data; we describe a new logistic output format that gives an estimate of probability of presence; finally we explore ‘‘background sampling’’ strategies that cope with sample selection bias and decrease model-building time. Our evaluation, based on a diverse dataset of 226 species from 6 regions, shows: 1) default settings tuned on presence-only data achieve performance which is almost as good as if they had been tuned on the evaluation data itself; 2) hinge features substantially improve model
Ecological risk assessments (ERAs) are employed to quantify and predict the vulnerability of a particular species, stock or population to a specific stressor, e.g. pollution, harvesting, climate change, by-catch. Data generated from ERAs are used to identify and prioritize species for implementation of effective conservation and management strategies. At this time, ERAs are of particular importance to elasmobranchs, given the ecological importance and documented global population declines of some elasmobranch species. Here, ERAs as a tool for elasmobranch conservation and management are reviewed and a theoretical roadmap provided for future studies. To achieve these goals, a brief history of ERAs and approaches used within them (in the context of elasmobranchs) are given, and a comprehensive review conducted of all ERA studies associated with elasmobranchs published between 1998 and 2011. The hazards assessed, species evaluated and methodological approaches taken are recorded. Chronological and geographical patterns suggest that this tool has grown in popularity as a commercial fishery management instrument, while also signalling a recent precautionary approach to elasmobranch management in commercial fisheries globally. The analysis demonstrates that the predominant parameters incorporated in previous ERAs are largely based on life-history characteristics, and sharks have received the majority of attention; batoids (including skates) have received less attention. Recreational fishing and habitat degradation are discussed as hazards which warrant future investigation through ERA. Lastly, suggestions are made for incorporating descriptive ecological data to aid in the continued development and evolution of this management tool as it applies to future elasmobranch conservation.
Predictive modeling and mapping based on the quantitative relationships between a species and the biophysical features (predictor variables) of the ecosystem in which it occurs can provide fundamental information for developing sustainable resource management policies for species and ecosystems. To create management strategies with the goal of sustaining a species such as sage grouse (Centrocercus urophasianus), whose distribution throughout North America has declined by approximately 50%, land management agencies need to know what attributes of the range they now inhabit will keep populations sustainable and which attributes attract disproportionate levels of use within a home range. The objectives of this study were to 1) quantify the relationships between sage grouse nest-site locations and a set of associated biophysical attributes using Maximum Entropy, 2) find the best subset of predictor variables that explain the data adequately, 3) create quantitative sage grouse distribution maps representing the relative likelihood of nest-site habitat based on those relationships, and 3) evaluate the implications of the results for future management of sage grouse. Nest-site location data from 1995 to 2003 were collected as part of a long-term research program on sage grouse reproductive ecology at Hart Mountain National Antelope Refuge. Two types of models were created: 1) with a set of predictor variables derived from digital elevation models, a field-validated vegetation classification, and UTM coordinates and 2) with the same predictors and UTM coordinates excluded. East UTM emerged as the most important predictor variable in the first type of model followed by the vegetation classification which was the most important predictor in the second type of model. The average training gain from ten modeling runs using all presence records and randomized background points was used to select the best subset of predictors. A predictive map of sage grouse nest-site habitat created from the application of the model to the study area showed strong overlap between model predictions and nest-site locations.
Diagnostic systems of several kinds are used to distinguish between two classes of events, essentially "signals" and "noise".
For them, analysis in terms of the "relative operating characteristic" of signal detection theory provides a precise and valid
measure of diagnostic accuracy. It is the only measure available that is uninfluenced by decision biases and prior probabilities,
and it places the performances of diverse systems on a common, easily interpreted scale. Representative values of this measure
are reported here for systems in medical imaging, materials testing, weather forecasting, information retrieval, polygraph
lie detection, and aptitude testing. Though the measure itself is sound, the values obtained from tests of diagnostic systems
often require qualification because the test data on which they are based are of unsure quality. A common set of problems
in testing is faced in all fields. How well these problems are handled, or can be handled in a given field, determines the
degree of confidence that can be placed in a measured value of accuracy. Some fields fare much better than others.
A central aim of ecology is to explain the heterogeneous distribution of biodiversity on earth. As expectations of diversity loss grow, this understanding is also critical for effective management and conservation. Although explanations for biodiversity patterns are still a matter for intense debate, they have often been considered to be scale-dependent. At large geographical scales, biogeographers have suggested that variation in species richness results from factors such as area, temperature, environmental stability, and geological processes, among many others. From the species pools generated by these large-scale processes, community ecologists have suggested that local-scale assembly of communities is achieved through processes such as competition, predation, recruitment, disturbances and immigration. Here we analyse hypotheses on speciation and dispersal for reef fish from the Indian and Pacific oceans and show how dispersal from a major centre of origination can simultaneously account for both large-scale gradients in species richness and the structure of local communities.
Recent studies document unprecedented declines in marine top predators that can initiate trophic cascades. Predicting the wider ecological consequences of these declines requires understanding how predators influence communities by inflicting mortality on prey and inducing behavioral modifications (risk effects). Both mechanisms are important in marine communities, and a sole focus on the effects of predator-inflicted mortality might severely underestimate the importance of predators. We outline direct and indirect consequences of marine predator declines and propose an integrated predictive framework that includes risk effects, which appear to be strongest for long-lived prey species and when resources are abundant. We conclude that marine predators should be managed for the maintenance of both density- and risk-driven ecological processes, and not demographic persistence alone.
Philopatry and regional connectivity of the great hammerhead shark
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Habitat suitability and environmental factors affecting whale shark (Rhincodon typus) aggregations in the Mexican Caribbean
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Maximum entropy modeling of species geographic distributions
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Vulnerability of Prionace glauca (L.) to longlining in the NE Atlantic
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Interpolation of animal tracking data in a fluid environment
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