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

Metabolic and nutritional condition of juvenile tiger sharks exposed to regional differences in coastal urbanization

How varying levels of human activity, such as proximity and size of the nearest market (i.e., market gravity), influence the nutritional ecology and physiological condition of highly migratory marine predators is poorly understood. In the present study, we used a non-lethal approach to compare the concentration of metabolic hormones (i.e. corticosteroids and thyroid hormones) and plasma fatty acids between juvenile female tiger sharks (Galeocerdo cuvier) sampled in two areas of the subtropical north Atlantic, which differed markedly in their levels of coastal urbanization, Florida and the Bahamas (high versus low, respectively). We hypothesized that juvenile female tiger sharks sampled in water surrounding high coastal urbanization (Florida), would exhibit evidence of lower prey quality and higher energetic demands as compared to individuals sampled in relatively less urbanized areas of Northern Bahamas. Results revealed that relative corticosteroid levels (a proxy for energy mobilization) were higher in juvenile female tiger sharks sampled in Florida; however, no differences were found in concentrations of thyroid hormones (proxies of energetic adjustments) between the two locations. We found higher percentages of omega-3 polyunsaturated fatty acids (indicative of high prey quality) in juvenile tiger sharks from Florida, whereas higher percentages of bacterial markers (often indicative of domestic sewage effluent) were detected in the individuals sampled in the Bahamas. Taken together, these findings do not suggest that the differences in nutritional quality and metabolic condition found between the two sampling locations can be fully attributed to foraging in areas exposed to differing levels of urbanization. We speculate that these patterns may be due to the highly migratory nature and generalist feeding strategy of this species, even at the juvenile life stage, as well as proximity of sampling locations from shore.

Physiological markers suggest energetic and nutritional adjustments in male sharks linked to reproduction

Energetic condition is one of the most important factors that influence fitness and reproductive performance in vertebrates. Yet, we lack evidence on how energetic states change in response to reproduction in large marine vertebrates. In the present study, we used a non-lethal approach to assess relationships among reproductive stage, circulating steroid hormones (testosterone and relative corticosteroid levels), plasma fatty acids, and the ketone body β-hydroxybutyrate in male sharks of two species with divergent ecologies, the benthic nurse shark (Ginglymostoma cirratum) and the epipelagic blacktip shark (Carcharhinus limbatus). We found higher relative corticosteroid levels in adult nurse sharks during the pre-mating period and in blacktip sharks during the mating period. Higher levels of β-hydroxybutyrate were found in adult nurse sharks during the mating period, but concentrations of this ketone body did not significantly vary across reproductive stages in blacktip sharks. We also detected reduced percentages of essential fatty acids during the mating period of both nurse and blacktip sharks. Taken together, our findings suggest that nurse and blacktip sharks differ in their energetic strategy to support reproduction, however, they likely rely on physiologically important fatty acids during mating, to support spermatogenesis.

Additional Pressure to a Threatened Species: High Persistent Organic Pollutant Concentrations in the Tropical Estuarine Batoid Gymnura altavela

Persistent organic pollutants (POPs) were determined in Gymnura altavela liver samples from one of the most impacted estuarine environments in the Atlantic Ocean (Guanabara Bay, Brazil). PCBs were the predominant compounds (91.2%) averaging 6773 ± 4659 ng.g^-1 lipid weight (lw). DDT, Mirex, HCH and HCB concentrations were 633 ± 715, 6.2 ± 9.3, 3.4 ± 1.4 and 0.5 ± 0.5 ng.g^-1 lw, respectively. Recent DDT input in the estuary was minimum, as verified by the p,p'-DDE/∑DDT ratio (0.67). The prevalence of industrial compounds was highlighted by the ΣDDT/ΣPCB ratio (0.08). A negative correlation detected between disc width and PCBs, Mirex and HCH concentrations may be a consequence of maternal offloading. High POP concentrations in G. altavela liver samples from Guanabara Bay suggests that PCBs, in particular, may pressure the conservation of this threatened with extinction tropical estuarine batoid species.

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.

The current knowledge gap on metallothionein mediated metal-detoxification in Elasmobranchs

Elasmobranchs are particularly vulnerable to environmental contamination, especially pollutants that may bioaccumulate and biomagnify, throughout the trophic web, such as metals. However, Elasmobranch management and conservation plans are challenging, and this group is often neglected regarding ecotoxicological analyses, particularly concerning metal detoxification mechanisms. This article discusses metallothionein (MT) mediated metal detoxification in Elasmobranchs and reflects on the current knowledge gap in this regard.

Effects of biological traits on capture-induced parturition in a freshwater stingray and perspectives for species management

Elasmobranchs are particularly vulnerable to overexploitation and population depletion, especially due to their life-history traits, such as low reproductive output and slow growth. Given that capture-induced parturition (abortion or premature birth) is a common consequence of fisheries in elasmobranchs, but still little studied, we investigated how the abortion/premature birth process varies in response to reproductive traits in a freshwater stingray, Potamotrygon amandae. Our results revealed that capture-induced parturition was affected by reproductive traits, such as litter size (one to seven) and gestation stage. The event occurred faster in pregnant females with high litter size during late pregnancy. Also, as found in other elasmobranchs, litter size was positively correlated with maternal size. These findings indicate that larger pregnant females in late pregnancy are more vulnerable to capture-induced parturition. This study improves our understanding of the capture-induced parturition process in stingrays, and provides useful information for management strategies and future recommendations for elasmobranch conservation.

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.