High microplastic and anthropogenic particle contamination in the gastrointestinal tracts of tiger sharks (Galeocerdo cuvier) caught in the western North Atlantic Ocean.

Few studies have documented microplastics (<5 mm) in shark gastrointestinal (GI) tracts. Here, we report microplastic contamination in the tiger shark (Galeocerdo cuvier), an apex predator and generalist feeder, at several different life stages. We examined seven stomachs and one spiral valve from eight individuals captured off the United States Atlantic and Gulf of Mexico coasts (eastern US) and conducted a literature review of publications reporting anthropogenic debris ingestion in elasmobranchs. Specimens were chemically digested in potassium hydroxide (KOH) and density separated using calcium chloride (CaCl2) before quantifying and categorizing suspected anthropogenic particles (>45 µm) by size, morphology, and colour. Anthropogenic particles were found in the stomachs and spiral valve of all sharks. A total of 3151 anthropogenic particles were observed across all stomachs with 1603 anthropogenic particles observed in a single specimen. A subset of suspected anthropogenic particles (14%) were chemically identified using Raman spectroscopy and µ-Fourier Transform Infrared spectroscopy to confirm anthropogenic origin. Overall, ≥95% of particles analyzed via spectroscopy were confirmed anthropogenic, with 45% confirmed as microplastics. Of the microplastics, polypropylene (32%) was the most common polymer. Diverse microparticle morphologies were found, with fragments (57%) and fibers (41%) most frequently observed. The high occurrence and abundance of anthropogenic particle contamination in tiger sharks is likely due to their generalist feeding strategy and high trophic position compared to other marine species. The literature review resulted in 32 studies published through 2022. Several methodologies were employed, and varying amounts of contamination were reported, but none reported contamination as high as detected in our study. Anthropogenic particle ingestion studies should continue in the tiger shark, in addition to other elasmobranch species, to further understand the effects of anthropogenic activities and associated pollution on these predators.

Evidence of increasing juvenile white sharks' (Carcharodon carcharias) habitat use at the Northern Channel Islands.

Juvenile white sharks (Carcharodon carcharias) typically aggregate along coastal beaches; however, high levels of recruitment and shifting oceanographic conditions may be causing habitat use expansions. Telemetry data indicate increased habitat use at the Northern Channel Islands (California, USA) by juvenile white shark that may be in response to increased population density at aggregation locations, or anomalous oceanographic events that impact habitat use or expand available habitat. Findings illustrate the need for long-term movement monitoring and understanding drivers of habitat use shifts and expansion to improve ecosystem management.

A biologging database of juvenile white sharks from the northeast Pacific.

Species occurrence records are vital data streams in marine conservation with a wide range of important applications. From 2001-2020, the Monterey Bay Aquarium led an international research collaboration to understand the life cycle, ecology, and behavior of white sharks (Carcharodon carcharias) in the southern California Current. The collaboration was devoted to tagging juveniles with animal-borne sensors, also known as biologging. Here we report the full data records from 59 pop-up archival (PAT) and 20 smart position and temperature transmitting (SPOT) tags that variously recorded pressure, temperature, and light-level data, and computed depth and geolocations for 63 individuals. Whether transmitted or from recovered devices, raw data files from successful deployments (n = 70) were auto-ingested from the manufacturer into the United States (US) Animal Telemetry Network's (ATN) Data Assembly Center (DAC). There they have attributed a full suite of metadata, visualized within their public-facing data portal, compiled for permanent archive under the DataONE Research Workspace member node, and are accessible for download from the ATN data portal.

Elasmobranch microbiomes: emerging patterns and implications for host health and ecology.

Elasmobranchs (sharks, skates and rays) are of broad ecological, economic, and societal value. These globally important fishes are experiencing sharp population declines as a result of human activity in the oceans. Research to understand elasmobranch ecology and conservation is critical and has now begun to explore the role of body-associated microbiomes in shaping elasmobranch health. Here, we review the burgeoning efforts to understand elasmobranch microbiomes, highlighting microbiome variation among gastrointestinal, oral, skin, and blood-associated niches. We identify major bacterial lineages in the microbiome, challenges to the field, key unanswered questions, and avenues for future work. We argue for prioritizing research to determine how microbiomes interact mechanistically with the unique physiology of elasmobranchs, potentially identifying roles in host immunity, disease, nutrition, and waste processing. Understanding elasmobranch-microbiome interactions is critical for predicting how sharks and rays respond to a changing ocean and for managing healthy populations in managed care.

Evaluation of muscle tissue as a non-lethal proxy for liver and brain organic contaminant loads in an elasmobranch, the Bonnethead Shark (Sphyrna tiburo).

Elasmobranch ecotoxicological investigations are complicated because accessing organs that accumulate organic contaminants is usually lethal. Several metrics among liver, muscle, and brain were evaluated to determine their relative organic contaminant loads and the efficacy of using muscle as a non-lethal proxy for liver. Liver contained the highest concentrations (368-4020 ng/g wet weigth [ww]) and greatest estimated total load of contaminants. Brain had higher toxin concentrations than muscle (4.18-84.2 ng/g ww versus 0.94-4.73 ng/g ww). Liver and brain were similar to each other in terms of contaminant detection occurrence and signature overlap, whereas muscle poorly reflected those of liver and brain. However, the identity of contaminants detected in muscle constituted those that substantially contributed to summed liver and brain concentrations. Thus, studies utilizing muscle as a non-lethal liver alternative to study organic contaminant exposure in elasmobranchs should craft questions with care, considering its limited ability to serve as an accurate proxy.

An inconvenient tooth: Evaluating female choice in multiple paternity using an evolutionarily and ecologically important vertebrate clade.

Understanding mating systems is a pillar of behavioural ecology, placing the complex interactions between females and males into a reproductive context. The field of multiple paternity, the phenomenon whereby many sires contribute to an individual litter, has traditionally viewed females as passive players in a male-male competitive framework. With the emergence of feminist perspectives in ecological fields, novel alternative mechanisms and evolutionary theories across invertebrate and vertebrate taxa recognize females are active stakeholders in the reproductive process. Despite their evolutionary significance, ecological diversity and myriad reproductive modes, elasmobranch (sharks, skates and rays) research lags behind other fields regarding complex biological processes, such as multiple paternity which is often ascribed to convenience polyandry. Here, we layout hypotheses and resynthesize multiple paternity literature from a female and life history perspective to highlight how alternative mechanisms influence the predominance of multiple paternity across elasmobranchs. We draw upon parallels in other invertebrate and vertebrate taxa to demonstrate how female elasmobranchs can influence multiple paternity outcomes that benefit their reproductive success. Our article challenges dogma that has resulted from years of dismissing the female perspective as important and provides a framework for future advancement using more holistic approaches to studying mating systems.

Elucidating shark diets with DNA metabarcoding from cloacal swabs.

Animal dietary information provides the foundation for understanding trophic relationships, which is essential for ecosystem management. Yet, in marine systems, high-resolution diet reconstruction tools are currently under-developed. This is particularly pertinent for large marine vertebrates, for which direct foraging behaviour is difficult or impossible to observe and, due to their conservation status, the collection of stomach contents at adequate sample sizes is frequently impossible. Consequently, the diets of many groups, such as sharks, have largely remained unresolved. To address this knowledge gap, we applied metabarcoding to prey DNA in faecal residues (fDNA) collected on cotton swabs from the inside of a shark's cloaca. We used a previously published primer set targeting a small section of the 12S rRNA mitochondrial gene to amplify teleost prey species DNA. We tested the utility of this method in a controlled feeding experiment with captive juvenile lemon sharks (Negaprion brevirostris) and on free-ranging juvenile bull sharks (Carcharhinus leucas). In the captive trial, we successfully isolated and correctly identified teleost prey DNA without incurring environmental DNA contamination from the surrounding seawater. In the field, we were able to reconstruct high-resolution teleost dietary information from juvenile C. leucas fDNA that was generally consistent with expectations based on published diet studies of this species. While further investigation is needed to validate the method for larger sharks and other species, it is expected to be broadly applicable to aquatic vertebrates and provides an opportunity to advance our understanding of trophic interactions in marine and freshwater systems.

Sublethal, sex-specific, osmotic, and metabolic impairments in embryonic and adult round stingrays from a location exposed to environmental contamination in southern California, USA.

Organic contaminants are known to affect a suite of physiological processes across vertebrate clades. However, despite their ancient lineage and important roles in maintaining healthy ecosystems, elasmobranchs (sharks, skates, and rays) are understudied with regard to sublethal effects of contaminant exposure on metabolic processes. Perturbations resulting from contaminant exposure can divert energy away from maintaining physiological homeostasis, particularly during energetically challenging life stages, such as pregnancy and embryonic development. Using the round stingray (Urobatis halleri) as a model elasmobranch species, we captured adult males and pregnant females (matrotrophic histotrophy) and their embryos from two populations differing in their environmental exposure to organic contaminants (primarily polychlorinated biphenyls (PCBs)). Pregnant females from the PCB-exposed population experienced significant decreases from early- to late-pregnancy in tissue mass and quality not seen in reference females. PCB-exposed pregnant females also failed to maintain plasma urea concentrations as pregnancy progressed, which was accompanied by a loss in muscle protein content. Despite the energetic demands of late-term pregnancy, females had significantly greater liver lipid content than reproductively inactive adult males. PCB-exposed adult males also had high metabolic capacity (i.e., enzyme activity) for most substrate groupings of all sex-site groups, suggesting that males may be even more negatively impacted by contaminant exposure than pregnant females. Evidence that in utero exposure to PCBs via maternal offloading impairs embryo outcomes is accumulating. Embryos from the PCB-contaminated site had lower tissue quality measures and indications that sex-based differences were manifesting in utero as males had higher metabolic capacities than females. This study indicates that accumulated PCB contaminants are not physiologically inert in the stingray.

Organic contaminants as an ecological tool to explore niche partitioning: a case study using three pelagic shark species.

Chemical contaminant profiles are linked to an animal's niche, providing a potential tool by which to assess resource partitioning in pelagic species. As proof of concept, we examined contaminant signatures in three species of sharks (Isurus oxyrinchus, Prionace glauca, and Alopias vulpinus) known to overlap in both space and time. Since these sharks comprise a predatory guild within the Southern California Bight (SCB), we predicted that species may partition spatial and dietary resources to limit the extent of competitive exclusion. Indeed, species were distinguishable by both total contaminant loads and their contaminant fingerprint, as random forest analysis found that species could be correctly classified 96% of the time. Our results demonstrate the utility of chemical analyses for ecological studies, and how contaminant tracers can be used in combination with traditional methods to elucidate how species may undergo niche partitioning to reduce competition for overlapping resources within predatory guilds.

Species-Specific Characteristics Influence Contaminant Accumulation Trajectories and Signatures Across Ontogeny in Three Pelagic Shark Species.

Factors influencing organic contaminant accumulation in sharks, especially across ontogeny, are not well-known. Contaminant concentrations were measured in three species of sharks (Blue, Shortfin Mako, and Common Thresher) across a range of size classes (neonatal to adult) that vary in their ecological and physiological characteristics. Empirical data was compared to a theoretical framework that predicted the shape of lifetime accumulation curves. We found that a one-size-fits-all accumulation model was not appropriate as species-specific characteristics had a significant effect on contaminant accumulation trajectories. Maternal offloading likely has an important effect on determining neonatal shark contaminant starting points, and trophic ecology and physiology may interact to affect the shape of species' contaminant accumulation curves. Makos were found to have the highest accumulation potential and Blues the lowest, with Threshers being intermediate in accumulation potential. Changes in species' ecology and/or physiology were also reflected in contaminant signature changes over ontogeny. If contaminant concentrations are to be used as a proxy for risk, species-specific characteristics need to be taken into account when estimating contaminant exposure and its potential negative effects on shark health and human consumption safety.

Quantifying habitat selection and variability in habitat suitability for juvenile white sharks.

While adult white sharks (Carcharodon carcharias) are apex predators with a circumglobal distribution, juvenile white sharks (JWS) feed primarily on bottom dwelling fishes and tend to be coastally associated. Despite the assumedly easier access to juveniles compared to large, migratory adults, limited information is available on the movements, environments, and distributions of individuals during this life stage. To quantify movement and understand their distribution in the southern California Bight, JWS were captured and fitted with dorsal fin-mounted satellite transmitters (SPOT tags; n = 18). Nine individuals crossed the U.S. border into Baja California, Mexico. Individuals used shallow habitats (134.96 ± 191.1 m) close to shore (7.16 ± 5.65 km). A generalized linear model with a binomial distribution was used to predict the presence of individuals based on several environmental predictors from these areas. Juveniles were found to select shallow habitats (< 1000 m deep) close to land (< 30 km of the shoreline) in waters ranging from 14 to 24°C. Southern California was found to be suitable eight months of the year, while coastal habitats in Baja California were suitable year-round. The model predicted seasonal movement with sharks moving from southern California to Baja California during winter. Additionally, habitat distribution changed inter-annually with sharks having a more northerly distribution during years with a higher Pacific Decadal Oscillation index, suggesting sharks may forego their annual fall migrations to Baja California, Mexico, during El Niño years. Model predictions aligned with fishery-dependent catch data, with a greater number of sharks being captured during periods and/or areas of increased habitat suitability. Thus, habitat models could be useful for predicting the presence of JWS in other areas, and can be used as a tool for potentially reducing fishery interactions during seasons and locations where there is increased susceptibility of incidental catch.

Legacy environmental polychlorinated biphenyl contamination attenuates the acute stress response in a cartilaginous fish, the Round Stingray.

In a population of Round Stingrays (Urobatis halleri) sampled from mainland California (polychlorinated biphenyl [PCB] exposed site, n = 46), relative to a nearby offshore island (reference site, n = 34), we tested the hypothesis that stingrays from the PCB-exposed site would have a compromised stress response. Adult male and pregnant female (pregnancy = matrotrophic histotrophy), stingrays were captured via hook and line at both locations over a breeding season and plasma was sampled either immediately (Baseline, males = 10, females = 31), or after ∼5 min of struggle on the line followed by a 15 min confinement stressor (Stressed, males = 16, females = 23). Biomarkers of the primary stress response (1α-OH-corticosterone) and the secondary response (energy mobilization; glucose, glycogen, and lactate in liver and muscle) were assessed. Females from both sites demonstrated the expected primary stress response of 1α-OH-corticosterone elevation, but the contaminant-exposed males did not. PCB-exposed stingrays, regardless of sex, failed to produce a plasma glucose increase in response to the applied stress, even though the stressor increased liver glucose as expected. This suggests a dysfunction in glucose transport due to PCB exposure. The Round Stingray accumulates lower PCB loads than other, predatory elasmobranchs, and by extension, the stress axis effects could be more severely impacted in those species as well. Lay summary Legacy polychlorinated biphenyl (PCB) contamination continues to adversely affect marine life. We show that PCB-exposure interferes with the ability of pregnant female and adult male stingrays to mobilize the energy necessary to respond appropriately to an acute stress like capture. Other cartilaginous fish species, such as sharks, accumulate considerably more PCB as a result of their predatory diet, and are likely to be more adversely impacted.

Steroid concentrations in maternal serum and uterine histotroph in round stingrays (Urobatis halleri).

Despite a wide range of elasmobranch (sharks, skates and rays) matrotrophic strategies, and thus potentially diverse pathways for maternal-fetal hormone exchange, little attention has been given to uterine steroids during development. Round Stingrays (Urobatis halleri) with matrotrophic histotrophy were captured during every month of their annual reproductive season from post-ovulation to near parturition, and paired samples of plasma and histotroph were analyzed for a suite of steroid hormones using LC-ESI/MRM. Hormone concentrations within and between maternal and uterine compartments were compared using two markers of embryo development. Histotroph had consistently higher detection rates and concentrations of hormones than maternal plasma, especially during early pregnancy when embryos are yolk sac-dependent for nutrition. Peaks in histotroph testosterone concentrations preceded maternal plasma, suggesting that hormones were locally produced within the uterine compartment. Embryonic sexual differentiation based on the presence of visible claspers (male copulatory organs) coincided with peaks in histotroph progesterone, testosterone, 17-hydroxyprogesterone and estradiol, suggesting that, like mammalian pregnancy, elasmobranch embryonic steroids also contribute to their own developmental environment.

Sex may influence environmental diphenhydramine accumulation in Round Stingrays.

Despite the amount of treated wastewater discharged into the Southern California Bight, few studies have examined pharmaceutical compounds in local biota. The Round Stingray (Urobatis halleri) was selected as a representative elasmobranch species to perform an exploratory study on environmental pharmaceutical exposure. Archived liver samples of males and females from juvenile to adult size classes from several locations (n = 53) were examined for 18 pharmaceutical and illicit drug compounds using isotope-dilution LC-MS/MS. Very few compounds were detected in stingray livers, with diphenhydramine as the only pharmaceutical above quantitation limits. Only stingrays collected from the urban site (mainland California) had detectable levels of diphenhydramine compared to no detections in reference stingrays (offshore island). Sex and sampling location substantially influenced both detection rate and concentrations. Our results suggest that aspects of species' ecology and physiology should be considered for future studies investigating pharmaceutical exposure in elasmobranchs.

An evaluation of body condition and morphometric relationships within southern California juvenile white sharks Carcharodon carcharias.

Length, mass and girth relationships are presented for 112 juvenile white sharks (JWS) Carcharodon carcharias caught in the Southern California Bight (SCB) nursery area between June 2008 and August 2017. No difference was found between male and female JWS length-mass relationships, but data suggest that JWS in the SCB gain more mass per unit length for the juvenile size classes compared with other C. carcharias populations. Condition-factor-to-liver-mass and condition-factor-to-liver-lipid-content relationships revealed that length and mass (i.e., condition factor) can be used as a non-invasive proxy for body condition for juveniles of this species. The parameters estimated in this study are key information for population assessments of juvenile C. carcharias in the north-east Pacific Ocean and will contribute to the conservation and management of this IUCN Red List Vulnerable species.

Legacy polychlorinated biphenyl contamination impairs male embryonic development in an elasmobranch with matrotrophic histotrophy, the round stingray (Urobatis halleri).

Anthropogenic chemical exposure can result in overall reductions in reproductive success. Using the round stingray (Urobatis halleri) as an elasmobranch model with internal gestation, we measured female fecundity and embryo growth from postovulation to near parturition to test the hypothesis that environmental polychlorinated biphenyl (PCB) contamination would impair reproductive success. Two sites were sampled from southern California, USA: the mainland site was exposed to legacy PCB contamination (with low exposure to other anthropogenic contaminants), and the offshore reference site at Catalina Island was a separate population with low anthropogenic influence. Contaminant-exposed embryos weighed less at each stage of development than reference embryos, while accumulating proportionately more liver mass over development. Furthermore, environmental contamination negatively affected male embryos more than female embryos. The present study is the first study to demonstrate a negative effect of contaminant exposure on elasmobranch embryo growth, with probable fitness costs later in life. Environ Toxicol Chem 2018;37:2904-2911. © 2018 SETAC.

Calcified cartilage or bone? Collagens in the tessellated endoskeletons of cartilaginous fish (sharks and rays).

The primary skeletal tissue in elasmobranchs -sharks, rays and relatives- is cartilage, forming both embryonic and adult endoskeletons. Only the skeletal surface calcifies, exhibiting mineralized tiles (tesserae) sandwiched between a cartilage core and overlying fibrous perichondrium. These two tissues are based on different collagens (Coll II and I, respectively), fueling a long-standing debate as to whether tesserae are more like calcified cartilage or bone (Coll 1-based) in their matrix composition. We demonstrate that stingray (Urobatis halleri) tesserae are bipartite, having an upper Coll I-based 'cap' that merges into a lower Coll II-based 'body' zone, although tesserae are surrounded by cartilage. We identify a 'supratesseral' unmineralized cartilage layer, between tesserae and perichondrium, distinguished from the cartilage core in containing Coll I and X (a common marker for mammalian mineralization), in addition to Coll II. Chondrocytes within tesserae appear intact and sit in lacunae filled with Coll II-based matrix, suggesting tesserae originate in cartilage, despite comprising a diversity of collagens. Intertesseral joints are also complex in their collagenous composition, being similar to supratesseral cartilage closer to the perichondrium, but containing unidentified fibrils nearer the cartilage core. Our results indicate a unique potential for tessellated cartilage in skeletal biology research, since it lacks features believed diagnostic for vertebrate cartilage mineralization (e.g. hypertrophic and apoptotic chondrocytes), while offering morphologies amenable for investigating the regulation of complex mineralized ultrastructure and tissues patterned on multiple collagens.

Who's My Daddy? Considerations for the influence of sexual selection on multiple paternity in elasmobranch mating systems.

Polyandry resulting in multiply-sired litters has been documented in the majority of elasmobranch species examined to date. Although commonly observed, reasons for this mating system remain relatively obscure, especially in batoids. The round stingray (Urobatis halleri) is an abundant, well-studied elasmobranch distributed throughout the northeastern Pacific that we used to explore hypotheses regarding multiple paternity in elasmobranchs. Twenty mid- to late-term pregnant females were sampled off the coast of southern California and their litters analyzed for the occurrence of multiple paternity using five nuclear microsatellite loci. In addition, embryo sizes and their position within the female reproductive system (i.e., right or left uterus) were recorded and used to make inferences for patterns of ovulation. Multiple paternity was observed in 90% of litters and male reproductive success within litters was relatively even among sires. High variability in testes mass was observed suggesting that sperm competition is high in this species, although male reproductive success per litter appeared to be relatively even. Using embryo size as a proxy for fertilization, females were found to exhibit a variety of ovulation patterns that could function to limit a male's access to eggs and possibly promote high rates of multiple paternity. Our study highlights that elasmobranch mating systems may be more varied and complex than presumed and further investigation is warranted.

Influence of ontogeny and environmental exposure on mercury accumulation in muscle and liver of male Round Stingrays.

Mercury tissue distribution and its dynamics are poorly understood in elasmobranchs. Total mercury was measured in liver and muscle of male Round Stingrays (Urobatis halleri) from Seal Beach, California, an anthropogenically impacted site, and from the offshore island of Santa Catalina, a less impacted site. Stable isotope analysis was also performed on the muscle and red blood cells (RBCs) of a subset of rays over a range of age classes to investigate mercury accumulation with respect to trophic ecology. Mercury in both tissues was found to be significantly greater in adults than juveniles in mainland rays; however, liver mercury accumulation drastically increased after maturity and was significantly greater in mainland adult rays than Catalina rays. There were no patterns in δ15N or δ13C with size in muscle; however, there were indications of seasonal changes in RBC δ15N, suggesting short term shifts in diet or behavior is likely linked to reproductive status as is mercury accumulation.

First evidence of persistent organic contaminants as potential anthropogenic stressors in the Barndoor Skate Dipturus laevis.

Although exploited populations of elasmobranchs may be able to recover from fishing pressure, there is little information regarding the Barndoor Skate's ability to cope with other anthropogenic stressors such as organic contaminants (OCs). Legacy OCs were measured in liver, muscle and ova from fourteen Barndoor Skates with mature skates having significantly greater mean concentrations of OCs than immature skates, demonstrating bioaccumulation with age. Using Toxic Equivalency Factors, skates were found to have levels of PCBs that have been shown to elicit negative physiological responses in other fishes and these results highlight the need for future studies to investigate the potential impacts that bioaccumulated organic contaminants have on the recovery and conservation of this vulnerable species.