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International audience; The management of migratory taxa relies on the knowledge of their movements. Among them, ontogenetic habitat shift, from nurseries to adult habitats, is a behavioural trait shared across marine taxa allowing resource partitioning between life stages and reducing predation risk. As this movement is consistent over time, characterizing its timing is critical to implement efficient management plans, notably in coastal areas to mitigate the impact of fisheries on juvenile stocks.In the Mexican Pacific, habitat use of the smooth hammerhead shark (Sphyrna zygaena) is poorly described, while the species is heavily harvested. Given the large uncertainties associated with the timing of out-migration from coastal nursery grounds to offshore waters prior to reproductive maturity, a more precise assessment of smooth hammerhead shark movements is needed.Photochemical degradation of mercury imparts mass-independent isotope fractionation (?Hg-199) which can be used to discriminate between neonate coastal shallow habitats and the offshore deep foraging patterns of late juveniles. Here, we present the application of muscle ?Hg-199 as molecular clocks to predict the timing of ontogenetic habitat shifts by smooth hammerhead sharks, based on their isotopic compositions at the initial and arrival habitats and on muscle isotopic turnover rate.We observed decreases in ?Hg-199 values with shark body length, reflecting increasing reliance on offshore mesopelagic prey with age. Coastal residency estimates indicated that smooth hammerhead sharks utilize coastal resources for 2 years prior to offshore migration, suggesting a prolonged residency in these ecosystems.Policy implications. This study demonstrates how mercury stable isotopes and isotopic clocks can be implemented as a complementary tool for stock management by predicting the timing of animal migration-a key aspect in the conservation of marine taxa. In the Mexican Pacific, fishing pressure on shark species occurs in coastal habitats depleting juvenile stocks. Consequently, management decision support tools are imperative for effectively maintaining early life stage population levels over time. The finding that smooth hammerhead sharks extensively rely on highly fished habitats for 2 years after parturition supports the relevance of establishing a size limit in coastal fisheries and demonstrates how the current temporal shark fishing closure could lack efficiency for the species.

Understanding the factors shaping patterns of ecological resilience is critical for mitigating the loss of global biodiversity. Throughout aquatic environments, highly mobile predators are thought to serve as important vectors of energy between ecosystems thereby promoting stability and resilience. However, the role these predators play in connecting food webs and promoting energy flow remains poorly understood in most contexts. Using carbon and nitrogen isotopes, we quantified the use of several prey resource pools (small oceanic forage, large oceanics, coral reef, and seagrass) by 17 species of elasmobranch fishes ( n = 351 individuals) in The Bahamas to determine their functional diversity and roles as ecosystem links. We observed remarkable functional diversity across species and identified four major groups responsible for connecting discrete regions of the seascape. Elasmobranchs were responsible for promoting energetic connectivity between neritic, oceanic and deep-sea ecosystems. Our findings illustrate how mobile predators promote ecosystem connectivity, underscoring their functional significance and role in supporting ecological resilience. More broadly, strong predator conservation efforts in developing island nations, such as The Bahamas, are likely to yield ecological benefits that enhance the resilience of marine ecosystems to combat imminent threats such as habitat degradation and climate change.

20 pages, 3 tables, 5 figures.-- Samantha Andrzejaczek ... et al.-- Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC), Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements, Data analysis was funded by the Bertarelli Foundation through the Marine Science program through grants to D.J.C., B.A.B., and S.A. D.J.C. is also funded through Research England, UK. S.A. and B.A.B. thank the Moore Foundation and the Packard Foundation. F.G.-M. thanks the Instituto Politecnico Nacional for fellowships (COFAA, EDI). S.B.W. thanks funding from the Darwin Initiative (DPLUS046). A.D.M.D. acknowledges funding from the Research and Conservation Budget at Georgia Aquarium, including philanthropic gifts from several anonymous donors. K.F. acknowledges funding from the Rolex Awards for Enterprise and the Whitley Fund for Nature

The isotopic composition of tooth-bound collagen has long been used to reconstruct dietary patterns of animals in extant and palaeoecological systems. For sharks that replace teeth rapidly in a conveyor-like system, stable isotopes of tooth collagen (δ13 CTeeth & δ15 NTeeth ) are poorly understood and lacking in ecological context relative to other non-lethally sampled tissues. This tissue holds promise, because shark jaws may preserve isotopic chronologies from which to infer individual-level ecological patterns across a range of temporal resolutions. Carbon and nitrogen stable isotope values were measured and compared between extracted tooth collagen and four other non-lethally sampled tissues of varying isotopic turnover rates: blood plasma, red blood cells, fin and muscle, from eight species of sharks. Individual-level isotopic variability of shark tooth collagen was evaluated by profiling teeth of different ages across whole jaws for the shortfin mako shark Isurus oxyrinchus and sandbar shark Carcharhinus plumbeus. Measurements of δ13 CTeeth and δ15 NTeeth were positively correlated with isotopic values from the four other tissues. Collagen δ13 C was consistently 13 C-enriched relative to all other tissues. Patterns for δ15 N were slightly less uniform; tooth collagen was generally 15 N-enriched relative to muscle and red blood cells, but congruent with fin and blood plasma (values clustered around a 1:1 relationship). Significant within-individual variability was observed across whole shortfin mako shark (δ13 C range = 1.4‰, δ15 N range = 3.6‰) and sandbar shark (δ13 C range = 1.2‰-2.4‰, δ15 N range = 1.7‰-2.4‰) jaws, which trended with tooth age. We conclude that amino acid composition and associated patterns of isotopic fractionation result in predictable isotopic offsets between tissues. Within-individual variability of tooth collagen stable isotope values suggests teeth of different ages may serve as ecological chronologies, that could be applied to studies on migration and individual-level diet variation across diverse time-scales. Greater understanding of tooth replacement rates, isotopic turnover and associated fractionation of tooth collagen will help refine potential ecological inferences, outlining clear goals for future scientific inquiry.

Hypomelanosis refers to a suite of skin pigment abnormalities, including albinism, leucism and piebaldism. While documented across many vertebrate species, examples of hypomelanosis are rarely seen in chondrichthyans, with little insight into the potential effects on survival. Here, we report the first observation of abnormal skin pigmentation indicative of piebaldism in the Atlantic nurse shark Ginglymostoma cirratum, representing only the second reported case of skin aberrations for this species. This extremely rare observation is discussed in the broader context of fitness variation and long-term survival.

Shark populations have declined across the Caribbean region, with negative associations between shark abundance and human population density, open access to fishing, and proximity to large markets (‘market gravity’). This decline is frequently attributed to fishing mortality, which increases in areas closer to humans and outside marine reserves. Although it is difficult to disentangle the effects of fishing mortality from other anthropogenic pressures on sharks, comparing shark abundance and diversity in jurisdictions with near zero fishing mortality versus prevalent shark fishing can demonstrate the role of overfishing. We used baited remote underwater video systems to compare shark abundance and diversity on coral reefs in 2 Caribbean nations with contrasting levels of shark exploitation: Belize (shark fishing) and The Bahamas (shark sanctuary). The abundance of targeted shark species and diversity were significantly higher in The Bahamas than in Belize. Caribbean reef and nurse shark abundance in Belize were best predicted by fishing-related factors (marine reserves, market gravity, their interaction). In The Bahamas, abiotic factors (depth, sea surface temperature) best predicted nurse shark abundance, while depth, market gravity, and its interaction with marine reserves predicted Caribbean reef shark abundance. These results indicate that fishing mortality reduces shark abundance and diversity in Belize, while lower fishing mortality in The Bahamas has greatly reduced but not eliminated human impacts on sharks. Future work should elucidate the indirect effects of humans to develop holistic shark conservation plans. We suggest minimizing shark fishing through multinational management plans to improve shark abundance and diversity, especially on reefs near densely populated areas.

The Caribbean reef shark (Carcharhinus perezi; Poey, 1876) is a medium to large-bodied coastal and reef-associated predator found throughout the subtropical and tropical waters of the Atlantic Ocean and Caribbean Sea, although its populations are increasingly threatened by overfishing. We describe the first mitochondrial genome sequence for this species, using Illumina MiSeq sequencing of an individual from The Bahamas. We report the mitogenome sequence of the Caribbean reef shark to be 16,709 bp and composed two rRNA genes, 22 tRNA genes, 13 protein-coding genes, 2 non-coding regions; the D-loop control region and the origin of light-strand replication. We discuss the implications of this new information on future monitoring efforts and conservation measures such as marine protected areas, and urge for greater application of mitochondrial studies of sharks in the Atlantic Ocean.

The oceanic whitetip shark Carcharhinus longimanus is a widely distributed large pelagic shark species once considered abundant in tropical and warm temperate waters, but recently listed as Critically Endangered by the IUCN due to drastic population declines associated with overfishing. In addition to risks posed to its populations due to overexploitation, oceanic whitetip sharks are also capable of accumulating elevated quantities of harmful environmental toxicants, placing them at special risk from anthropogenic pollution. Herein, we provide the first data on accumulation of the toxic, non-essential metal mercury (Hg) in northwest Atlantic (NWA) oceanic whitetip sharks, focusing on aggregations occurring at Cat Island, The Bahamas. Total Hg (THg) concentrations were measured in muscle of 26 oceanic whitetip sharks and compared with animal length and muscle δ15N to evaluate potential drivers of Hg accumulation. THg concentrations were also measured in fin and blood subcomponents (red blood cells and plasma) to determine their value as surrogates for assessing Hg burden. Muscle THg concentrations were among the highest ever reported for a shark species and correlated significantly with animal length, but not muscle δ15N. Fin, red blood cell, and plasma THg concentrations were significantly correlated with muscle THg. Fin THg content was best suited for use as a surrogate for estimating internal Hg burden because of its strong relationship with muscle THg levels, whereas blood THg levels may be better suited for characterizing recent Hg exposure. We conclude that Hg poses health risks to NWA oceanic whitetip sharks and human consumers of this species.

The development of the isotopic niche, an n-dimensional hypervolume (with n being the number of isotopes) occupied by a population in delta space, has revolutionized the study of animal interactions in wild populations. While the isotopic niche offers a useful means to understand interactions at many ecological resolutions (e.g., individual, population, community, ecosystem), a variety of intrinsic and extrinsic factors drive isotopic variability and influence the ultimate geometry of observed niche dimensions. Here, we provide an updated synthesis to guide the application of bulk stable isotope ratios to study ecological niches. We summarize progress in the application of bulk stable isotope ratios for evaluating niches to synthesize a formal definition of the isotopic niche. We identify six broad categories to describe drivers of isotopic variance introduced by the animal, its environment, and the researcher, and provide recommendations to account for such variations before, during, and after sample collection and data analyses. Our synthesis illustrates the considerations that should be made before employing the isotopic niche to broader ecological contexts, and offers guidance for the use and interpretation of isotopic niche dynamics in future studies.

The purpose of this study was to test the effects of high CO2 exposure on wound healing rates in an elasmobranch fish (Urobatis jamaicensis). Small dermal injuries (8 mm biopsy) closed by 22 days post wounding with a decrease in haematocrit. High CO2 exposure (ΔpH = 1.4) did not influence healing rate or haematocrit. Combined, these data provide evidence that minimally invasive scientific procedures have short-term impacts on elasmobranch fishes even during exposure to a chronic stressor. Therefore, wound healing rates may not be strongly impacted by ocean acidification (ΔpH = 0.4).

Understanding how intraspecific variation in the use of prey resources impacts energy metabolism has strong implications for predicting long-term fitness and is critical for predicting population-to-community level responses to environmental change. Here, we examine the energetic consequences of variable prey resource use in a widely distributed marine carnivore, juvenile sand tiger sharks (Carcharias taurus). We used carbon and nitrogen isotope analysis to identify three primary prey resource pools-demersal omnivores, pelagic forage, and benthic detritivores and estimated the proportional assimilation of each resource using Bayesian mixing models. We then quantified how the utilization of these resource pools impacted the concentrations of six plasma lipids and how this varied by ontogeny. Sharks exhibited variable reliance on two of three predominant prey resource pools: demersal omnivores and pelagic forage. Resource use variation was a strong predictor of energetic condition, whereby individuals more reliant upon pelagic forage exhibited higher blood plasma concentrations of very low-density lipoproteins, cholesterol, and triglycerides. These findings underscore how intraspecific variation in resource use may impact the energy metabolism of animals, and more broadly, that natural and anthropogenically driven fluctuations in prey resources could have longer term energetic consequences.

Nitrogen isotope (δ

Nitrogen stable isotopes (δ15N) are typically used to estimate trophic position, providing insight into ecological roles and broader food web structure. Ecological inferences drawn from these estimates rely on quantification of isotopic baselines, i.e., low trophic level organisms reflecting the predominant nitrogen sources that support food web biomass. When baselines vary due to environmental (e.g., temperature) or anthropogenic factors (e.g., nutrient run-off), interpretation of trophic position based on δ15N may not be ecologically sound. Here, we tested the effects of assuming stable versus spatially variable δ15N baselines used to estimate the trophic position of a cosmopolitan estuarine predator—juvenile bull sharks (Carcharhinus leucas). Sampling across the San Antonio Bay system, TX, USA revealed that baseline consumers exhibited spatially variable δ15N values, which were strongly associated with capture salinity representing the influence of anthropogenically introduced nitrogen largely from fluvial run-off. As a result, estimates of bull shark trophic position differed based on baseline assumptions—sharks exhibited an ontogenetic shift in trophic position when spatial variability of baseline δ15N was accounted for, while an uncorrected approach indicated no relationship between body size and trophic position. Diet data supported ontogenetic shifts in bull shark diets, with increased consumption of larger-bodied prey among older individuals. Evaluation of isotopic baselines in spatially dynamic ecosystems like estuaries is essential, especially for highly mobile species like sharks that traverse dynamic isoscapes. A literature review revealed that only 16% of studies leveraging stable isotopes to assess the trophic ecology of sharks have accounted for potential spatial variability of isotopic baselines. As such, greater consideration of variability in isotopic baselines is important moving forward considering the ubiquitous application of this technique by ecologists.

Skates (class Chondrichthyes; subclass Elasmobranchii; order Rajiformes; family Rajidae) comprise one quarter of extant chondrichthyans, yet have received little attention in the scientific literature likely due to their relatively low economic value and difficulties in species identification. The absence of species‐specific information on catch, life history and migration of skates has often precluded the development of single‐species stock assessments and led to the use of cursory multispecies assessments, which lack the ability to track species‐specific catch and abundance trends. This has resulted in undetected local extirpations, as has been previously reported for common (Dipturus batis, Rajidae), white (Rostroraja alba, Rajidae) and long‐nose (Dipturus oxyrhinchus, Rajidae) skates in the Irish Sea. Here, we (a) use case studies to illustrate how the perception of skate population structure and stock status has historically been masked through multispecies assessment and management practices, (b) review current information on the movement of skates and identify gaps in knowledge, and (c) identify biases associated with the use of various tagging technologies, which have confounded our understanding of movement and migration ecology of skates. Considering that over 40% of extant Rajidae species are listed as “Data Deficient” by the International Union for Conservation of Nature, we illustrate a critical need to broaden the current understanding of skate life history, movement and migration ecology by providing recommendations on the further application of electronic tags and biogeochemical natural tags in movement studies and highlight the benefits that studies using these approaches have for novel management frameworks.

The isotopic composition of tooth-bound collagen has long been used to reconstruct dietary patterns of animals in extant and palaeoecological systems. For sharks that replace teeth rapidly in a conveyor-like system, stable isotopes of tooth collagen (δ

The notion that closely related species resemble each other in ecological niche space (i.e., phylogenetic dependence) has been a long‐standing, contentious paradigm in evolutionary biology, the incidence of which is important for predicting the ecosystem‐level effects of species loss. Despite being examined across a multitude of terrestrial taxa, many aspects of niche conservatism have yet to be explored in marine species, especially for characteristics related to resource use and trophic behavior (Eltonian niche characteristics, ENCs). We combined ENCs derived from stable isotope ratios at assemblage‐ and species‐levels with phylogenetic comparative methods, to test the hypotheses that benthic marine fishes (1) exhibit similar assemblage‐wide ENCs regardless of geographic location and (2) display phylogenetically dependent ENCs at the species level. We used a 12‐species sub‐set of the monophyletic group Rajidae sampled from three independent assemblages (Central California, Gulf of Alaska, and Northwest Atlantic), which span two ocean basins. Assemblage‐level ENCs implied low trophic diversity and high evenness, suggesting that Rajidae assemblages may exhibit a well‐defined trophic role, a trend consistent regardless of geographic location. At the species level, we found evidence for phylogenetic dependence of ENCs relating to trophic diversity (i.e., isotopic niche width; SEAc). Whether individuals can be considered functional equivalents across assemblages is hard to ascertain because we did not detect a significant phylogenetic signal for ENCs relating to trophic function (e.g., trophic position). Thus, additional, complimentary approaches are required to further examine the phylogenetic dependence of species functionality. Our approach illustrates the potential of stable isotope‐derived niche characteristics to provide insight on macroecological processes occurring across evolutionary time, which could help predict how assemblages may respond to the effects of species loss.

As concerns about anthropogenic and natural disturbance grow, understanding animal resource use patterns has been increasingly prioritized to predict how changes in environmental conditions, food web structure, and population dynamics will affect biological resilience. Among the tools used to assess resource use, stable isotope analysis has proliferated in ecological studies, particularly in relation to describing intra- and interspecific variation in trophic interactions. Despite a growing need to disseminate scientific information, the inherent limitations of stable isotope ratios and inappropriate synonymizing of distinct evolutionary and ecological processes may mislead ecological inferences in natural systems. This situation necessitates a re-evaluation of the utility of stable isotope ratios to address certain ecological questions. Here, we assess the efficacy of stable isotope ratios to describe two fundamental ecological processes, niche partitioning and individual specialization. Investigation of these processes has increased substantially in accordance with increased access to stable isotope data. This article discusses the circumstances and approaches that are necessary to evaluate niche partitioning and individual specialization, and outlines key considerations for the associated application of stable isotope ratios.

18 pages, 5 figures, supplementary data https://doi.org/10.1016/j.biocon.2021.109175.-- The data supporting the findings of this study are available in the Supplementary Materials (Appendix 3–5, Table A3-A5). Raw datasets (where available) and results summary tables for each analysis of human mobility and empirical datasets are deposited in a github repository: https://github.com/rjcommand/PAN-Environment, The global lockdown to mitigate COVID-19 pandemic health risks has altered human interactions with nature. Here, we report immediate impacts of changes in human activities on wildlife and environmental threats during the early lockdown months of 2020, based on 877 qualitative reports and 332 quantitative assessments from 89 different studies. Hundreds of reports of unusual species observations from around the world suggest that animals quickly responded to the reductions in human presence. However, negative effects of lockdown on conservation also emerged, as confinement resulted in some park officials being unable to perform conservation, restoration and enforcement tasks, resulting in local increases in illegal activities such as hunting. Overall, there is a complex mixture of positive and negative effects of the pandemic lockdown on nature, all of which have the potential to lead to cascading responses which in turn impact wildlife and nature conservation. While the net effect of the lockdown will need to be assessed over years as data becomes available and persistent effects emerge, immediate responses were detected across the world. Thus initial qualitative and quantitative data arising from this serendipitous global quasi-experimental perturbation highlights the dual role that humans play in threatening and protecting species and ecosystems. Pathways to favorably tilt this delicate balance include reducing impacts and increasing conservation effectiveness, The Canada Research Chairs program provided funding for the core writing team. Field research funding was provided by A.G. Leventis Foundation; Agence Nationale de la Recherche, [grant number ANR-18-32–0010CE-01 (JCJC PEPPER)]; Agencia Estatal de Investigaci; Agência Regional para o Desenvolvimento da Investigação Tecnologia e Inovação (ARDITI), [grant number M1420-09-5369-FSE-000002]; Alan Peterson; ArcticNet; Arkadaşlar; Army Corp of Engineers; Artificial Reef Program; Australia's Integrated Marine Observing System (IMOS), National Collaborative; Research Infrastructure Strategy (NCRIS), University of Tasmania; Australian Institute of Marine Science; Australian Research Council, [grant number LP140100222]; Bai Xian Asia Institute; Batubay Özkan; BC Hydro Fish and Wildlife Compensation Program; Ben-Gurion University of the Negev; Bertarelli Foundation; Bertarelli Programme in Marine Science; Bilge Bahar; Bill and Melinda Gates Foundation; Biology Society of South Australia; Boston University; Burak Över; California State Assembly member Patrick O'Donnell; California State University Council on Ocean Affairs, Science & Technology; California State University Long Beach; Canada Foundation for Innovation (Major Science Initiative Fund and funding to Oceans Network Canada), [grant number MSI 30199 for ONC]; Cape Eleuthera Foundation; Centre National d'Etudes Spatiales; Centre National de la Recherche Scientifique; Charles Darwin Foundation, [grant number 2398]; Colombian Institute for the Development of Science and Technology (COLCIENCIAS), [grant number 811–2018]; Colombian Ministry of Environment and Sustainable Development, [grant number 0041–2020]; Columbia Basin Trust; Commission for Environmental Cooperation; Cornell Lab of Ornithology; Cultural practices and environmental certification of beaches, Universidad de la Costa, Colombia, [grant number INV.1106–01–002-15, 2020–21]; Department of Conservation New Zealand; Direction de l'Environnement de Polynésie Française; Disney Conservation Fund; DSI-NRF Centre of; Excellence at the FitzPatrick Institute of African Ornithology; Ecology Project International; Emin Özgür; Environment and Climate Change Canada; European Community: RTD programme - Species Support to Policies; European Community's Seventh Framework Programme; European Union; European Union's Horizon 2020 research and innovation programme, Marie Skłodowska-Curie, [grant number 798091, 794938]; Faruk Eczacıbaşı; Faruk Yalçın Zoo; Field research funding was provided by King Abdullah University of Science and Technology; Fish and Wildlife Compensation Program; Fisheries and Oceans Canada; Florida Fish and Wildlife Conservation Commission, [grant numbers FWC-12164, FWC-14026, FWC-19050]; Fondo Europeo de Desarrollo Regional; Fonds québécois de la recherche nature et technologies; Foundation Segré; Fundação para a Ciência e a Tecnologia (FCT Portugal); Galapagos National Park Directorate research, [grant number PC-41-20]; Gordon and Betty Moore Foundation, [grant number GBMF9881 and GBMF 8072]; Government of Tristan da Cunha; Habitat; Conservation Trust Foundation; Holsworth Wildlife Research Endowment; Institute of Biology of the Southern Seas, Sevastopol, Russia; Instituto de Investigación de Recursos Biológicos Alexander von Humboldt; Instituto Nacional de Pesquisas Espaciais (INPE), Brazil; Israeli Academy of Science's Adams Fellowship; King Family Trust; Labex, CORAIL, France; Liber Ero Fellowship; LIFE (European Union), [grant number LIFE16 NAT/BG/000874]; María de Maeztu Program for Units of Excellence in R&D; Ministry of Science and Innovation, FEDER, SPASIMM,; Spain, [grant number FIS2016–80067-P (AEI/FEDER, UE)]; MOE-Korea, [grant number 2020002990006]; Mohamed bin Zayed Species Conservation Fund; Montreal Space for Life; National Aeronautics and Space Administration (NASA) Earth and Space Science Fellowship Program; National Geographic Society, [grant numbers NGS-82515R-20]; National Natural Science Fund of China; National Oceanic and Atmospheric Administration; National Parks Board, Singapore; National Science and Technology Major Project of China; National Science Foundation, [grant number DEB-1832016]; Natural Environment Research Council of the UK; Natural Sciences and Engineering Research Council of Canada (NSERC), Alliance COVID-19 grant program, [grant numbers ALLRP 550721–20, RGPIN-2014-06229 (year: 2014), RGPIN-2016-05772 (year: 2016)]; Neiser Foundation; Nekton Foundation; Network of Centre of Excellence of Canada: ArcticNet; North Family Foundation; Ocean Tracking Network; Ömer Külahçıoğlu; Oregon State University; Parks Canada Agency (Lake Louise, Yoho, and Kootenay Field Unit); Pew Charitable Trusts; Porsim Kanaf partnership; President's International Fellowship Initiative for postdoctoral researchers Chinese Academy of Sciences, [grant number 2019 PB0143]; Red Sea Research Center; Regional Government of the Azores, [grant number M3.1a/F/025/2015]; Regione Toscana; Rotary Club of Rhinebeck; Save our Seas Foundation; Science & Technology (CSU COAST); Science City Davos, Naturforschende Gesellschaft Davos; Seha İşmen; Sentinelle Nord program from the Canada First Research Excellence Fund; Servizio Foreste e Fauna (Provincia Autonoma di Trento); Sigrid Rausing Trust; Simon Fraser University; Sitka Foundation; Sivil Toplum Geliştirme Merkezi Derneği; South African National Parks (SANParks); South Australian Department for Environment and Water; Southern California Tuna Club (SCTC); Spanish Ministry for the Ecological Transition and the Demographic Challenge; Spanish Ministry of Economy and Competitiveness; Spanish Ministry of Science and Innovation; State of California; Sternlicht Family Foundation; Suna Reyent; Sunshine Coast Regional Council; Tarea Vida, CEMZOC, Universidad de Oriente, Cuba, [grant number 10523, 2020]; Teck Coal; The Hamilton Waterfront Trust; The Ian Potter Foundation, Coastwest, Western Australian State NRM; The Red Sea Development Company; The Wanderlust Fund; The Whitley Fund; Trans-Anatolian Natural Gas Pipeline; Tula Foundation (Hakai Institute); University of Arizona; University of Pisa; US Fish and Wildlife Service; US Geological Survey; Valencian Regional Government; Vermont Center for Ecostudies; Victorian Fisheries Authority; VMRC Fishing License Fund; and Wildlife Warriors Worldwide, With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S

Large-scale migrations present challenges to management of exploited or at-risk marine species. Our understanding of predator movements has greatly improved, but data are often inadequate to understand patterns on population scales. The chemical composition of predator tissues, most often stable isotope ratios of carbon and nitrogen (δ‎13C and δ‎15N), provides markers of movement as predators incorporate discrete regional isotopic signatures throughout their migratory pathways. These signals can be analysed from small quantities of various tissues (e.g. muscle, liver, blood, hair, feathers) all of which provide different timescales of movement. Predator physiology mediates the assimilation and turnover rates of stable isotopes in tissues, providing a temporal element to interpretation of predator isotopic signatures. Combining physiology-mediated isotopic turnover rates and geographic ‘isoscapes’ of regional isotopic gradients allows for isotopic clock estimates of predator migration timing, which can be used to generate population-scale estimates of retrospective movements using large datasets across targeted regions and sampling periods. This allows for improved regional and international management and conservation of mobile species across their migratory ranges.

We determined concentrations of Hg, Pb, Cd, Cr, As, Ni, Ag, Se, Cu, and Zn in muscle tissue of six commonly consumed Long Island fish species (black seabass, bluefish, striped bass, summer flounder, tautog, and weakfish, total sample size = 1211) caught off Long Island, New York in 2018 and 2019. Long-term consumption of these coastal fish could pose health risks largely due to Hg exposure; concentrations of the other trace elements were well below levels considered toxic for humans. By combining the measured Hg concentrations in the fish (means ranging from 0.11 to 0.27 mg/kg among the fish species), the average seafood consumption rate, and the current US EPA Hg reference dose (0.0001 mg/kg/d), it was concluded that seafood consumption should be limited to four fish meals per month for adults for some fish (bluefish, tautog) and half that for young children. Molar ratios of Hg:Se exceeded 1 for some black seabass, bluefish, tautog, and weakfish.

The purpose of this study was to test the effects of high CO

We used stable isotope analysis to examine ontogenetic patterns in the resource use dynamics of bonefish (Albula vulpes) collected from two locations (Banks and Atlantic) within the coastal waters of Eleuthera, The Bahamas. A marked shift in δ13C signatures between leptocephali and juveniles reflected a rapid change in resource use, likely from pelagic to alternate neritic sources of primary production. Ontogenetic shifts in habitat use were observed across bonefish from both sides of Eleuthera, but direction of the isotopic shifts varied. Bonefish from the Atlantic side demonstrated an enrichment in 13C with size, whereas the opposite pattern was observed for individuals captured from the Banks. Differences are likely to be explained by the variability of primary production sources, which dominate each side of the island (i.e., more reliance on seagrass with ontogeny on the Atlantic side, versus a shift to macroalgal-dominated foodwebs with growth on the Banks side). Enrichment in 15N with body size was observed for both locations and reflects the ability to utilize a broader range of prey items with increasing gape size. Trophic diversity (inferred through nitrogen range), however, was lower on the Banks side, suggesting that reduced prey diversity may limit the increase in dietary shifts that gape size increases typically allow. A significant positive relationship between δ13C and whole-body energy density (MJ kg-1) in adults on the Banks side was observed. Adult bonefish that forage in seagrasses likely benefit from higher energy densities from selected prey items, and may explain this result. Data from this study reinforces the importance of a diversity of habitats in supporting bonefish throughout ontogeny.

Recent studies on shark assemblages on the northeast Florida and southeast Georgia coast (hereafter referred to collectively as the "First Coast") have demonstrated differences in species and age-class composition of catch from previously characterized estuaries and newly surveyed area beaches, demonstrating that these regions may provide a critical habitat to different segments (i.e., life stages) of local shark populations. In this study, carbon and nitrogen stable isotopes (δ13 C and δ15 N) from muscle tissue and blood plasma were used to examine trophic dynamics (and temporal variability thereof) of the three dominant co-occurring species found along First Coast beaches (the Atlantic Sharpnose shark Rhizoprionodon terraenovae, Blacknose shark Carcharhinus acronotus and Blacktip shark Carcharhinus limbatus) to determine if they exhibit overlap in resource use along with spatial and temporal habitat use. Although considered spatially segregated from the beach species, a dominant, age-class species found in First Coast estuaries (juvenile Sandbar sharks Carcharhinus plumbeus) was also included in this analysis for comparison. Temporal variability of resource-use characteristics was detected at the species level. Resource-use overlap among species varied by tissue type and was generally higher for blood plasma, suggesting greater resource sharing over more recent time periods. Over longer time periods Atlantic Sharpnose and Blacktip sharks exhibited resource-use expansion, whereas Blacknose sharks exhibited a narrowing in resource use, suggesting a more specialized foraging strategy compared to the other species. The resource-use breadth of Sandbar sharks also expanded between blood plasma and muscle tissue. Significant size relationships were detected in Blacktip and Sandbar sharks, indicating ontogenetic resource shifts for both species. A diversity of highly productive resource pools likely support shark populations along the First Coast such that resource-use differentiation is not required to facilitate species co-occurrence. This work may shed light on understanding patterns of species co-occurrence as well as aid in future conservation efforts.

Carbon and nitrogen stable isotopes (δ13C and δ15N) were used to examine trophic niche dynamics of three co-occurring predators in The Bahamas. Variable estimates of core trophic niche width and total trophic niche overlap were observed between nurse sharks (Ginglymostoma cirratum), southern stingrays (Hypanus americanus), and Atlantic chupare stingrays (Styracura schmardae). Nurse sharks exhibited little trophic overlap with either species of stingray and exhibited higher δ15N values, suggesting limited potential resource competition. Southern and Atlantic chupare stingrays exhibited higher total trophic niche overlap, highlighting higher levels of resource competition. Nurse sharks exhibited the broadest δ13C range, implying utilization of multiple resource pools to facilitate energetic requirements, compared with southern stingrays and Atlantic chupare stingrays. Southern stingrays exhibited the smallest core trophic niche width, highlighting reliance upon a narrower range of resource pools, likely supported by a single habitat type. We postulate that the persistence of the three sub-sampled predator populations is supported by potential resource partitioning and utilization of multiple trophic resource pools. Further information regarding trophic niche dynamics and patterns of resource use is required for data-poor species to identify how populations and communities may respond to the adverse effects of exploitation, such as fisheries impacts, habitat alteration, and pollution.

Evaluating tissue fractionation between mothers and their offspring is fundamental for informing our interpretation of stable isotope values in young individuals and can provide insight into the dynamics of maternal provisioning. The objectives of this study were to investigate the isotopic relationships between maternal reproductive (i.e., yolk, yolk-sac placenta) and somatic tissues (i.e., muscle and liver) relative to embryos in the Bonnethead Shark Sphyrna tiburo, to evaluate the fractionation of stable carbon (δ13C) and nitrogen (δ15N) isotopes between these tissues. Additionally, we examined intra-uterine variability in the isotopic relationships to ascertain whether this species may exhibit variable nutrient allocation. Embryos showed similar magnitudes of enrichment in 13C (i.e., Δδ13C, difference between adult and embryo) relative to adult tissues (Δδ13C = ~1.0‰). However, embryos were depleted in 15N relative to adult muscle tissues (Δδ15N = −1.0‰), a finding that contrasts Δδ15N values reported for other placentotrophic sharks. Embryo-muscle Δδ15N was correlated with length, supporting the contention that the magnitude of enrichment between embryonic and maternal tissues results from the shift from yolk to placental feeding. Embryo δ15N and Δδ15N values showed significant intra-uterine variability; a result not observed for δ13C and Δδ13C values. The contrasting patterns in fractionation among placentotrophic sharks highlight the importance of evaluating these relationships across elasmobranch taxa with consideration for different tissues, reproductive strategies and stages of gestation. The divergent findings support future evaluation of stable isotope relationships between mothers and offspring for purposes of estimating inherent isotopic variability and how this variability may inform physiological and dietary mechanisms.

Lipids affect stable isotope values generated for marine fishes, however these effects remain poorly described for many extant shark taxa, especially deep-sea species. Here, we report the effects of lipid extraction (LE) on δ13C, δ15N, and C:N values of seven deep-sea sharks, generate novel mathematical normalizations for δ13C based on the relationship between bulk and lipid extracted values (δ13CBulk and δ13CLE) and examine whether common normalized correction models provide a robust method for addressing lipid-biasing effects in two species, the Cuban dogfish (Squalus cubensis; n = 20), and Greenland shark (Somniosus microcephalus; n = 24). LE generally resulted in enrichment of 13C and 15N, but produced variable effects on C:N across all species. Novel mathematical normalizations for δ13C were derived from the pooled shark community, and a single species-specific correction was generated for the Cuban dogfish, but could not be determined for the Greenland shark. Four common lipid correction models used for teleosts, failed to accurately predict δ13C values statistically similar to δ13CLE, in both Cuban dogfish and Greenland sharks, likely due to the confounding effects of lipids and urea on C:N. These observations suggest that chemical lipid extraction should be a mandatory procedure prior to interpreting stable isotope data for deep-sea sharks, at least for those species where lipid effects are large.

Knowledge of the spatial ecology and movement of animals contributes to our understanding of intra- and inter-specific interactions and ecosystem dynamics, and can inform conservation actions. Here we assessed the space use and activity levels of a marine predator, the Caribbean reef shark (Carcharhinus perezi), in coastal regions of Eleuthera, The Bahamas over a 60-day period using acoustic telemetry. Of the 14 adult sharks (eight males, six females) tagged with acoustic transmitters (equipped with accelerometer sensor), nine were detected in a 14 km2 gridded receiver array. Male sharks were significantly less likely to be detected over time relative to females. Given post-release survival is typically high in C. perezi, this finding may indicate that males have larger home ranges and may exhibit lower site fidelity compared to females. Patterns of space use indicated C. perezi primarily occupied the outer reef shelf and were rarely detected on the interior of the reef. Shark activity levels (inferred from acceleration profiles) were highest in close proximity to the reef shelf. Our findings indicate C. perezi individuals frequently occupy deeper water habitats, but make forays into reef shelf habitats where high activity levels are likely related to foraging.