Accumulation of Per- and Polyfluoroalkyl Substances (PFAS) in Coastal Sharks from Contrasting Marine Environments: The New York Bight and The Bahamas.

Per- and polyfluoroalkyl substances (PFAS) enter the marine food web, accumulate in organisms, and potentially have adverse effects on predators and consumers of seafood. However, evaluations of PFAS in meso-to-apex predators, like sharks, are scarce. This study investigated PFAS occurrence in five shark species from two marine ecosystems with contrasting relative human population densities, the New York Bight (NYB) and the coastal waters of The Bahamas archipelago. The total detected PFAS (∑PFAS) concentrations in muscle tissue ranged from 1.10 to 58.5 ng g-1 wet weight, and perfluorocarboxylic acids (PFCAs) were dominant. Fewer PFAS were detected in Caribbean reef sharks (Carcharhinus perezi) from The Bahamas, and concentrations of those detected were, on average, ∼79% lower than in the NYB sharks. In the NYB, ∑PFAS concentrations followed: common thresher (Alopias vulpinus) > shortfin mako (Isurus oxyrinchus) > sandbar (Carcharhinus plumbeus) > smooth dogfish (Mustelus canis). PFAS precursors/intermediates, such as 2H,2H,3H,3H-perfluorodecanoic acid and perfluorooctanesulfonamide, were only detected in the NYB sharks, suggesting higher ambient concentrations and diversity of PFAS sources in this region. Ultralong-chain PFAS (C ≥ 10) were positively correlated with nitrogen isotope values (δ15N) and total mercury in some species. Our results provide some of the first baseline information on PFAS concentrations in shark species from the northwest Atlantic Ocean, and correlations between PFAS, stable isotopes, and mercury further contextualize the drivers of PFAS occurrence.

Assessing contemporary Arctic habitat availability for a woolly mammoth proxy.

Interest continues to grow in Arctic megafaunal ecological engineering, but, since the mass extinction of megafauna ~ 12-15 ka, key physiographic variables and available forage continue to change. Here we sought to assess the extent to which contemporary Arctic ecosystems are conducive to the rewilding of megaherbivores, using a woolly mammoth (M. primigenius) proxy as a model species. We first perform a literature review on woolly mammoth dietary habits. We then leverage Oak Ridge National Laboratories Distributive Active Archive Center Global Aboveground and Belowground Biomass Carbon Density Maps to generate aboveground biomass carbon density estimates in plant functional types consumed by the woolly mammoth at 300 m resolution on Alaska's North Slope. We supplement these analyses with a NASA Arctic Boreal Vulnerability Experiment dataset to downgrade overall biomass estimates to digestible levels. We further downgrade available forage by using a conversion factor representing the relationship between total biomass and net primary productivity (NPP) for arctic vegetation types. Integrating these estimates with the forage needs of woolly mammoths, we conservatively estimate Alaska's North Slope could support densities of 0.0-0.38 woolly mammoth km-2 (mean 0.13) across a variety of habitats. These results may inform innovative rewilding strategies.

Linking vertical movements of large pelagic predators with distribution patterns of biomass in the open ocean.

Many predator species make regular excursions from near-surface waters to the twilight (200 to 1,000 m) and midnight (1,000 to 3,000 m) zones of the deep pelagic ocean. While the occurrence of significant vertical movements into the deep ocean has evolved independently across taxonomic groups, the functional role(s) and ecological significance of these movements remain poorly understood. Here, we integrate results from satellite tagging efforts with model predictions of deep prey layers in the North Atlantic Ocean to determine whether prey distributions are correlated with vertical habitat use across 12 species of predators. Using 3D movement data for 344 individuals who traversed nearly 1.5 million km of pelagic ocean in [Formula: see text]42,000 d, we found that nearly every tagged predator frequented the twilight zone and many made regular trips to the midnight zone. Using a predictive model, we found clear alignment of predator depth use with the expected location of deep pelagic prey for at least half of the predator species. We compared high-resolution predator data with shipboard acoustics and selected representative matches that highlight the opportunities and challenges in the analysis and synthesis of these data. While not all observed behavior was consistent with estimated prey availability at depth, our results suggest that deep pelagic biomass likely has high ecological value for a suite of commercially important predators in the open ocean. Careful consideration of the disruption to ecosystem services provided by pelagic food webs is needed before the potential costs and benefits of proceeding with extractive activities in the deep ocean can be evaluated.

Quantifying longline bycatch mortality for pelagic sharks in western Pacific shark sanctuaries.

Marine protected areas are increasingly touted for their role in conserving large marine predators such as sharks, but their efficacy is debated. Seventeen "shark sanctuaries" have been established globally, but longline fishing continues within many such jurisdictions, leading to unknown levels of bycatch mortality levels. Using public data from Global Fishing Watch and Regional Fisheries Management Organizations, we quantified longline fishing within eight shark sanctuaries and estimated pelagic shark catch and mortality for seven pelagic shark species. Sanctuary mortality ranged from 600 individuals (Samoa) to 36,256 individuals (Federated States of Micronesia), equivalent to ~5% of hypothesized sustainable levels for blue sharks to ~40% for silky sharks, with high mortality levels in the Federated States of Micronesia, Palau, and the Marshall Islands. Unsustainable mortality rates were exceeded for silky sharks in two sanctuaries, highlighting a need for additional stock assessments and implementation of bycatch reduction measures. Big data integration workflows represent a transformative tool in fisheries management, particularly for data-poor species.

Energetic connectivity of diverse elasmobranch populations - implications for ecological resilience.

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.

Observations of hypomelanosis in the nurse shark Ginglymostoma cirratum.

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.

Tiger sharks support the characterization of the world's largest seagrass ecosystem.

Seagrass conservation is critical for mitigating climate change due to the large stocks of carbon they sequester in the seafloor. However, effective conservation and its potential to provide nature-based solutions to climate change is hindered by major uncertainties regarding seagrass extent and distribution. Here, we describe the characterization of the world's largest seagrass ecosystem, located in The Bahamas. We integrate existing spatial estimates with an updated empirical remote sensing product and perform extensive ground-truthing of seafloor with 2,542 diver surveys across remote sensing tiles. We also leverage seafloor assessments and movement data obtained from instrument-equipped tiger sharks, which have strong fidelity to seagrass ecosystems, to augment and further validate predictions. We report a consensus area of at least 66,000 km2 and up to 92,000 km2 of seagrass habitat across The Bahamas Banks. Sediment core analysis of stored organic carbon further confirmed the global relevance of the blue carbon stock in this ecosystem. Data from tiger sharks proved important in supporting mapping and ground-truthing remote sensing estimates. This work provides evidence of major knowledge gaps in the ocean ecosystem, the benefits in partnering with marine animals to address these gaps, and underscores support for rapid protection of oceanic carbon sinks.

Capture heats up sharks.

Catch-and-release fishing is an important component of ecotourism industries and scientific research worldwide, but its total impact on animal physiology, health and survival is understudied for many species of fishes, particularly sharks. We combined biologging and blood chemistry to explore how this fisheries interaction influenced the physiology of two widely distributed, highly migratory shark species: the blue shark (Prionace glauca) and the tiger shark (Galeocerdo cuvier). Nineteen sharks were caught by drum line or rod-and-reel angling; subcutaneous body temperature measurements were taken immediately upon capture, with six individuals also providing subsequent subcutaneous body temperature measurements via biologging as they swam freely for several hours post-release. We found that short-term capture caused shark body temperature to increase significantly and rapidly, with increases of 0.6°C-2.7°C for blue sharks (mean, 1.2 ± 0.6°C) and 0.5°C-0.9°C for tiger sharks (mean, 0.7 ± 0.2°C) and with capture-induced heating rates of blue sharks averaging 0.3°C min-1 but as high as 0.8°C min-1. Blue shark body temperature was even higher deeper into the white muscle. These heating rates were three to eight times faster than maximum rates encountered by our biologging sharks swimming through thermally stratified waters and faster than most acute heating experiments conducted with ectotherms in laboratory experiments. Biologging data showed that body temperatures underwent gradual decline after release, returning to match water temperatures 10-40 mins post-release. Blood biochemistry showed variable lactate/glucose levels following capture; however, these concentrations were not correlated with the magnitude of body temperature increase, nor with body size or hooking time. These perturbations of the natural state could have immediate and longer-term effects on the welfare and ecology of sharks caught in catch-and-release fisheries and we encourage further study of the broader implications of this reported phenomenon.

The movement ecology of fishes.

Movement of fishes in the aquatic realm is fundamental to their ecology and survival. Movement can be driven by a variety of biological, physiological and environmental factors occurring across all spatial and temporal scales. The intrinsic capacity of movement to impact fish individually (e.g., foraging) with potential knock-on effects throughout the ecosystem (e.g., food web dynamics) has garnered considerable interest in the field of movement ecology. The advancement of technology in recent decades, in combination with ever-growing threats to freshwater and marine systems, has further spurred empirical research and theoretical considerations. Given the rapid expansion within the field of movement ecology and its significant role in informing management and conservation efforts, a contemporary and multidisciplinary review about the various components influencing movement is outstanding. Using an established conceptual framework for movement ecology as a guide (i.e., Nathan et al., 2008: 19052), we synthesized the environmental and individual factors that affect the movement of fishes. Specifically, internal (e.g., energy acquisition, endocrinology, and homeostasis) and external (biotic and abiotic) environmental elements are discussed, as well as the different processes that influence individual-level (or population) decisions, such as navigation cues, motion capacity, propagation characteristics and group behaviours. In addition to environmental drivers and individual movement factors, we also explored how associated strategies help survival by optimizing physiological and other biological states. Next, we identified how movement ecology is increasingly being incorporated into management and conservation by highlighting the inherent benefits that spatio-temporal fish behaviour imbues into policy, regulatory, and remediation planning. Finally, we considered the future of movement ecology by evaluating ongoing technological innovations and both the challenges and opportunities that these advancements create for scientists and managers. As aquatic ecosystems continue to face alarming climate (and other human-driven) issues that impact animal movements, the comprehensive and multidisciplinary assessment of movement ecology will be instrumental in developing plans to guide research and promote sustainability measures for aquatic resources.

Ocean warming alters the distributional range, migratory timing, and spatial protections of an apex predator, the tiger shark (Galeocerdo cuvier).

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.

Space use patterns of sharks in relation to boat activity in an urbanized coastal waterway.

Aquatic ecosystems face numerous anthropogenic threats associated with coastal urbanization, with boat activity being among the most prevalent. The present study aimed to evaluate a potential relationship between boat activity and shark space use in Biscayne Bay, Florida (USA), a coastal waterway exposed to high levels of boating. Spatiotemporal patterns in boat density and traffic were determined from aerial surveys and underwater acoustic recorders, respectively. These data were then compared with residency patterns of bull (Carcharhinus leucas), nurse (Ginglymostoma cirratum) and great hammerhead (Sphyrna mokarran) sharks quantified through passive acoustic telemetry. Results were mixed, with no detectable relationship between boat density and shark residency for any of the species. Hourly presence of G. cirratum decreased with increasing boat traffic, a relationship not seen in the other two species. Explanations for these results include habituation of sharks to the high levels of chronic boat activity in the study area and interspecific differences in hearing sensitivity.

Complete mitochondrial genome of the Caribbean reef shark, Carcharhinus perezi (Carcharhinformes: Carcharhinidae).

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.

Metal concentrations in coastal sharks from The Bahamas with a focus on the Caribbean Reef shark.

Over the last century anthropogenic activities have rapidly increased the influx of metals and metalloids entering the marine environment, which can bioaccumulate and biomagnify in marine top consumers. This may elicit sublethal effects on target organisms, having broad implications for human seafood consumers. We provide the first assessment of metal (Cd, Pb, Cr, Mn, Co, Cu, Zn, As, Ag, and THg) and metalloid (As) concentrations in the muscle tissue of coastal sharks from The Bahamas. A total of 36 individual sharks from six species were evaluated, spanning two regions/study areas, with a focus on the Caribbean reef shark (Carcharhinus perezi), and to a lesser extent the tiger shark (Galeocerdo cuvier). This is due their high relative abundance and ecological significance throughout coastal Bahamian and regional ecosystems. Caribbean reef sharks exhibited some of the highest metal concentrations compared to five other species, and peaks in the concentrations of Pb, Cr, Cu were observed as individuals reached sexual maturity. Observations were attributed to foraging on larger, more piscivorous prey, high longevity, as well a potential slowing rate of growth. We observed correlations between some metals, which are challenging to interpret but may be attributed to trophic level and ambient metal conditions. Our results provide the first account of metal concentrations in Bahamian sharks, suggesting individuals exhibit high concentrations which may potentially cause sublethal effects. Finally, these findings underscore the potential toxicity of shark meat and have significant implications for human consumers.

Variation of body condition and plasma energy substrates with life stage, sex, and season in wild-sampled nurse sharks Ginglymostoma cirratum.

Reported here are the relationships among morphological (i.e., body condition) and biochemical (i.e., plasma concentrations of triglycerides, cholesterol, free fatty acids, and ketone bodies and ketone body ratios) parameters related to energy storage and use, as well as the variation of such parameters, for 107 free-ranging nurse sharks Ginglymostoma cirratum sampled off South Florida. Immature G. cirratum exhibited a higher variance in body condition, plasma free fatty acid concentrations and ketone body ratios compared to adults. Mature female G. cirratum had significantly higher body condition than mature males, driven by a seasonal increase in mature female body condition during the wet season. Mature male G. cirratum showed a decrease in the ketone body ß-hydroxybutyric acid during the dry season. Taken together, this study provides a baseline assessment of body condition and internal physiological state for a data-poor marine species and demonstrates significant ontogenetic, sexual and seasonal variation in G. cirratum energetic state. As concluded by other studies of energy metabolism in free-ranging sharks, this research highlights the importance of considering intraspecific patterns and sampling context for inferring the drivers of variation.

Effects of exposure to large sharks on the abundance and behavior of mobile prey fishes along a temperate coastal gradient.

Top predators can exert strong influences on community structure and function, both via direct, consumptive effects, as well as through non-consumptive, fear-based effects (i.e. predation risk). However, these effects are challenging to quantify, particularly for mobile predators in marine ecosystems. To advance this field of research, here we used baited remote underwater video stations (BRUVs) to assess how the behavior of mobile fish species off Cape Cod, Massachusetts, was affected by exposure to large sharks. We categorized sites into three levels of differential shark predation exposure (white sharks, Carcharodon carcharias) and quantified the relative abundance and arrival times (elapsed time before appearing on screen) for six mobile fish prey groups to the BRUV stations. Increased large shark exposure was associated with a decrease in overall prey abundance, but the overall response was prey group-specific. Foraging of smooth dogfish, a likely important prey item for large sharks in the system, was significantly reduced in areas frequented by white sharks. Specifically, the predicted probabilities of smooth dogfish bait contacts or bite attempts occurring were reduced by factors of 5.7 and 8.4, respectively, in areas of high exposure as compared to low exposure. These modifications were underscored by a decrease in smooth dogfish abundance in areas of high exposure as well. Our results suggest that populations of large, roving sharks may induce food-related costs in prey. We discuss the implications of this work within the context of the control of risk (COR) hypothesis, for the purposes of advancing our understanding of the ecological role and effects of large sharks on coastal marine ecosystems.

Access to Highly Functionalized Cyclopentenones via Diastereoselective Pauson-Khand Reaction of Siloxy-Tethered 1,7-Enynes.

A diastereoselective Co2(CO)8-mediated Pauson-Khand reaction (PKR) of siloxy-tethered 1,7-enynes for the synthesis of cyclopentaoxasilinones has been developed. This transformation can be performed on a multigram scale and is characterized by a broad substrate scope, functional group compatibility, and high chemo- and diastereoselectivity. Oxidation of the resulting cyclopentaoxasilinones delivers stereoenriched ß-alkylated cyclopentenones, which are inaccessible by intermolecular PKRs. This research provides a practical solution to the challenges associated with the classical intermolecular PKR.

Conservation genetics of the bonnethead shark Sphyrna tiburo in Bocas del Toro, Panama: Preliminary evidence of a unique stock.

The bonnethead shark, Sphyrna tiburo, is a small elasmobranch distributed in the Eastern Pacific from southern California to Ecuador, and along the Western Atlantic, with preferences for continental margins of North, Central and South America, the Gulf of Mexico, and the Caribbean. Recent studies have suggested that it could be under a process of cryptic speciation, with the possibility to find different species in similar geographic locations. Here we assessed the population structure and genetic diversity of this highly philopatric and non-dispersive species in the Bocas del Toro Archipelago, Panama. Fragments of the mitochondrial genes cytochrome oxidase I and control region, were used to test the genetic structure of adult and juvenile S. tiburo in this area, and were compared with other locations of the Western Atlantic and Belize. We found significant genetic differentiation between Caribbean bonnethead sharks from Bocas del Toro and Belize, when compared to bonnetheads from other locations of the Western Atlantic. These results also suggest that Bocas del Toro could constitute a different genetic population unit for this species, whereby bonnethead sharks in this area could belong to a unique stock. The information obtained in this study could improve our understanding of the population dynamics of the bonnethead shark throughout its distribution range, and may be used as a baseline for future conservation initiatives for coastal sharks in Central America, a poorly studied an often overlooked region for shark conservation and research.

Effects of predator exposure on baseline and stress-induced glucocorticoid hormone concentrations in pumpkinseed Lepomis gibbosus.

We compared baseline and maximal cortisol concentrations between predator exposure and prey blood samples in pumpkinseed Lepomis gibbosus, captured using a standardised fishing event underneath osprey Pandion haliaetus nests and away from osprey nests. We did not detect differences in cortisol or glucose between sites. These findings suggest that predictable sources of predation risk may not confer stress-related costs in teleosts.