peer reviewed | Elasmobranchs can bioaccumulate considerable amounts of persistent organic pollutants (POPs) and utilize several reproductive strategies thereby influencing maternal transfer of contaminants. This study provides preliminary data on the POP transfer from pregnant females to offspring of three species (Atlantic stingrays, bonnethead, blacktip sharks) with different reproduction modes (aplacental, placental viviparity). Polychlorinated biphenyl (PCB) levels were generally higher than any other POPs. Stingrays and blacktip shark embryos contained the lowest POP concentrations while bonnetheads and the blacktip adult female had the highest concentrations. Results suggest that are more readily transferred from the mother to the embryo compared to what is transferred to ova in stingrays. Statistically significant differences in levels of selected POPs were found between embryos from the left and right uterus within the same litter as well as between female and male embryos within the same litter for bonnetheads, but not for the blacktip sharks.

International audience | Bioindicator species are increasingly valuable in environmental pollution monitoring, and elasmobranch species include many suitable candidates for that role. By measuring contaminants and employing biomarkers of effect inrelevant elasmobranch species, scientists may gain important insights about the impacts of pollution in marine ecosystems. This review compiles biomarkers applied in elasmobranchs to assess the effect of pollutants (e.g.,metals, persistent organic pollutants, and plastics), and the environmental changes induced by anthropogenic activities (e.g., shifts in marine temperature, pH, and oxygenation). Over 30 biomarkers measured in more than12 species were examined, including biotransformation biomarkers (e.g., cytochrome P450 1A), oxidative stress-related biomarkers (e.g., superoxide anion, lipid peroxidation, catalase, and vitamins), stress proteins (e.g., heatshock protein 70), reproductive and endocrine biomarkers (e.g., vitellogenin), osmoregulation biomarkers (e.g., trimethylamine N-oxide, Na+/K+-ATPase, and plasma ions), energetic and neurotoxic biomarkers (e.g., lactatedehydrogenase, lactate, and cholinesterases), and histopathological and morphologic biomarkers (e.g., tissue lesions and gross indices).

This study analyzes microplastic ingestion by three deep-water elasmobranch species (Galeus melastomus, Scyliorhinus canicula and Etmopterus spinax) from the Tyrrhenian Sea, discriminating between stomach and intestine contents. The absence of significant differences in frequency and abundance of plastic items into stomachs seems to suggest that ecological diversity among the three sharks does not strongly influence the probability of plastic ingestion in the study area. On the other hand, the detected differences in the microplastic content into the intestine might be due to a different retention time of microplastics, suggesting how feeding habits could influence metabolic features, and therefore affect the recovery of ingested plastic items. This information would improve the future development of marine micro-litter monitoring systems, following the MSFD requirements. Moreover, this study shows that all the three examined elasmobranch species can give important information even with relatively small sample sizes (N ≈ 30), and they could be used as target species for monitoring micro-litter ingestion in deep-water habitats.

Persistent organic pollutants (POPs), including Perfluoroalkyl substances (PFASs), enter into the marine ecosystem, raising questions on possible adverse effects caused to the health of marine organisms and especially of top predators. Thus, there is an urge to assess the occurrence and the tissue distribution of PFASs in apex predators. To this end, the current study examines concentrations and distribution of 15 PFASs among 85 samples of different tissues from 9 shark and ray species collected in Greece. The results showed a similar PFAS pattern among the different tissues, with long carbon chain PFASs being the most frequently detected compounds. PFTrDA was the most predominant compound in terms of concentration and frequency of detection, followed by PFUnDA and PFOS. PFTrDA concentrations ranged between < LOQ and 27.1 ng/g ww, while PFUnDA and PFOS levels ranged from <LOQ to 16.0 and < LOQ to 21.6 ng/g ww, respectively. Regarding their frequency of detection, PFTrDA and PFUnDA were detected in 98% and 91% of the samples, respectively, while PFOS was detected in 79%. ΣPFAS concentrations in each analysed tissue ranged from 0.3 to 85 ng/g ww, with the latter being detected in the liver of angular roughshark (Oxynotus centrina). On average, PFASs were found to be accumulated in tissues in the following order: gonads > heart > liver ≈ gills > muscle. Relative contribution (%) of individual compounds to ΣPFAS concentration varied among the different shark tissues, and also among the different shark species. No correlation between PFASs levels in tissues and sharks’ gender, length and geographical origin was observed.

Mercury (Hg) exposure poses a threat to both fish and human health. Sharks are known to bioaccumulate Hg, however, little is known regarding how Hg is distributed between different tissue groups (e.g. muscle regions, organs). Here we evaluated total mercury (THg) concentrations from eight muscle regions, four fins (first dorsal, left and right pectorals, caudal-from both the inner core and trailing margin of each fin), and five internal organs (liver, kidney, spleen, heart, epigonal organ) from two different shark species, bonnethead (Sphyrna tiburo) and silky shark (Carcharhinus falciformis) to determine the relationships of THg concentrations between and within tissue groups. Total Hg concentrations were highest in the eight muscle regions with no significant differences in THg concentrations between the different muscle regions and muscle types (red and white). Results from tissue collected from any muscle region would be representative of all muscle sample locations. Total Hg concentrations were lowest in samples taken from the fin inner core of the first dorsal, pectoral, and caudal (lower lobe) fins. Mercury concentrations for samples taken from the trailing margin of the dorsal, pectoral, and caudal fins (upper and lower lobe) were also not significantly different from each other for both species. Significant relationships were found between THg concentrations in dorsal axial muscle tissue and the fin inner core, liver, kidney, spleen and heart for both species as well as the THg concentrations between the dorsal fin trailing margin and the heart for the silky shark and all other sampled tissue types for the bonnethead shark. Our results suggest that biopsy sampling of dorsal muscle can provide data that can effectively estimate THg concentrations in specific organs without using more invasive, or lethal methods.

Polychlorinated biphenyls (PCBs) chiral signatures were measured in Greenland sharks (Somniosus microcephalus) and their potential prey in arctic marine food webs from Canada (Cumberland Sound) and Europe (Svalbard) to assess temporal and spatial variation in PCB contamination at the stereoisomer level. Marine mammals had species-specific enantiomer fractions (EFs), likely due to a combination of in vivo biotransformation and direct trophic transfer. Greenland sharks from Cumberland Sound in 2007–2008 had similar EFs to those sharks collected a decade ago in the same location (PCBs 91, 136 and 149) and also similar to their conspecifics from Svalbard for some PCB congeners (PCBs 95, 136 and 149). However, other PCB EFs in the sharks varied temporally (PCB 91) or spatially (PCB 95), suggesting a possible spatiotemporal variation in their diets, since biotransformation capacity was unlikely to have varied within this species from region to region or over the time frame studied.

Blue shark score among the most abundant, widely distributed and worldwide consumed elasmobranchs. In this work contents of PCBs, PCDD/Fs and PBDEs were studied by means of GC-HRMS in muscle and liver of sixty blue sharks from the North East Atlantic sampled in 2019. Concentrations relatively similar were found for PCBs and PCDD/Fs in comparison with those in Atlantic specimens from the same area sampled in 2015. In contrast, PBDE loads doubled, likely mirroring the increased environmental presence of these pollutants. This, together with the different congener profiles reported for the same species in other geographical areas, highlighted the blue shark's potential as bioindicator of the degree and fingerprints of regional pollution by POPs. Interesting dissimilarities between muscle and liver concentrations were detected, most likely ascribed to distinct toxicokinetics involved for the different pollutants. Whereas most POPs preferentially accumulated in liver, some did the opposite in muscle. BDE-209 was the most prominent example, being almost negligible its presence in liver (0.3%) while accounting for ca. 14% of the total PBDE content in muscle. Different findings in this regard described for other shark species call for focused research to ascertain the role of the species in this apparent favored metabolization of BDE-209 in the liver. From a consumption perspective, the concentrations found in muscle -the most relevant part in the human diet-for PCBs and dioxin-like POPs were below the EU maximum allowed levels in foodstuff. Conversely, in liver about 58% and 78% of samples overpassed the European levels for tolerable intake of i-PCBs and dioxin POPs, respectively. Concentrations of PBDEs exceeded EQS (0.0085 ng/g w.w.) established by the European Water Framework Directive in 100% and 92% of liver and muscle samples, respectively, which adds to the open debate of such as a reduce value for this current EQS.

The silky shark Carcharhinus falciformis is a large pelagic species distributed in the global oceans and was recently listed as “Vulnerable” by the IUCN because of its decline in population due to overfishing. As an apex predator, the silky shark can accumulate elevated quantities of mercury (Hg), posing a potential risk to its remaining population. In this study, total Hg (THg) concentrations were determined in silky shark muscle, liver, dermis, red blood cells (RBC) and plasma sampled from the eastern tropical Pacific, and δ¹⁵N values were measured to explore the influence of feeding ecology on Hg accumulation. The highest THg concentrations were in muscle (7.81 ± 6.70 μg g⁻¹ dry weight (dw) or 2.14 ± 1.83 μg g⁻¹ wet weight (ww)) and liver (7.88 ± 10.22 μg g⁻¹ dw or 4.66 ± 6.04 μg g⁻¹ ww) rather than dermis, RBC and plasma. The THg concentrations in all tissue types were significantly correlated with fork length and showed faster accumulation rates after maturity. Maternal THg transfer was observed in silky sharks with embryos having 33.16% and 1.98% in muscle and liver compared with their respective mothers. The potentially harmful THg concentrations in silky shark tissues and embryos may lead to health problems of sharks and consumers. THg concentrations were negatively correlated with δ¹⁵N values for all tissues, indicating likely baseline variations in δ¹⁵N values that reflect changes in the foraging habitats or regions of silky sharks with size or age. Lastly, strong correlations were observed among THg concentrations of all tissue types, indicating that nonlethal sampling of muscle and dermis tissue can be used effectively to quantify THg concentration of other internal tissues.

In coastal ecosystems, top predators are exposed to a wide variety of nutrient and contaminant sources due to the diversity of trophic webs within inshore marine habitats. Mercury contamination could represent an additional threat to shark populations that are declining worldwide. Here we measured total mercury, carbon and nitrogen isotopes, as well as mercury isotopes, in two co-occurring shark species (the bull shark Carcharhinus leucas and the tiger shark Galeocerdo cuvier) and their potential prey from a coastal ecosystem of the western Indian Ocean (La Réunion Island). Our primary goals were to (i) determine the main trophic Hg sources for sharks and (ii) better characterize their diet composition and foraging habitat. Hg isotope signatures (Δ¹⁹⁹Hg and δ²⁰²Hg) of shark prey suggested that bull sharks were exposed to methylmercury (MeHg) produced in offshore epipelagic waters, while tiger sharks were exposed to offshore mesopelagic MeHg with additional microbial transformation in slope sediments. Δ¹⁹⁹Hg values efficiently traced the ecology of the two predators, demonstrating that bull sharks targeted coastal prey in shallow waters while tiger sharks were mainly foraging on mesopelagic species in the deeper waters of the island slope. Unexpectedly, we found a positive shift in δ²⁰²Hg (>1‰) between sharks and their prey, leading to high δ²⁰²Hg values in the two shark species (e.g. 1.91 ± 0.52‰ in bull sharks). This large shift in δ²⁰²Hg indicates that sharks may display strong MeHg demethylation abilities, possibly reflecting evolutionary pathways for mitigating their MeHg contamination.

The decline of shark populations in the world ocean is affecting ecosystem structure and function in an unpredictable way and new ecological information is today needed to better understand the role of sharks in their habitats. In particular, the characterization of foraging patterns is crucial to understand and foresee the evolution of dynamics between sharks and their prey. Many shark species use the mesopelagic area as a major foraging ground but the degree to which different pelagic sharks rely on this habitat remains overlooked. In order to depict the vertical dimension of their trophic ecology, we used mercury stable isotopes in the muscle of three pelagic shark species (the blue shark Prionace glauca, the shortfin mako shark Isurus oxyrinchus and the smooth hammerhead shark Sphyrna zygaena) from the northeastern Pacific region. The Δ¹⁹⁹Hg values, ranging from 1.40 to 2.13‰ in sharks, suggested a diet mostly based on mesopelagic prey in oceanic habitats. We additionally used carbon and nitrogen stable isotopes (δ¹³C, δ¹⁵N) alone or in combination with Δ¹⁹⁹Hg values, to assess resource partitioning between the three shark species. Adding Δ¹⁹⁹Hg resulted in a decrease in trophic overlap estimates compared to those based on δ¹³C/δ¹⁵N alone, demonstrating that multi-isotope modeling is needed for accurate trophic description of the three species. Mainly, it reveals that they forage at different average depths and that resource partitioning is mostly expressed through the vertical dimension within pelagic shark assemblages. Concomitantly, muscle total mercury concentration (THg) differed between species and increased with feeding depth. Overall, this study highlights the key role of the mesopelagic zone for shark species foraging among important depth gradients and reports new ecological information on trophic competition using mercury isotopes. It also suggests that foraging depth may play a pivotal role in the differences between muscle THg from co-occurring high trophic level shark species.