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Environmental context Mercury (Hg) is a non-essential metal that can accumulate in aquatic biota, including top predators such as elasmobranchs (sharks and rays) and biomagnifying along the trophic web. This study provides data on Hg total, methylmercury (MeHg) and stable isotopes (δ13C and δ15N) for 13 elasmobranch taxa in the Equatorial Western Atlantic Ocean, relating biological and ecological properties with Hg concentrations and the estimated human consumption risk. Rationale Elasmobranchs widely consume fish, making understanding Hg bioaccumulation crucial. Little is known about Hg distribution in their bodies beyond muscle tissue and the associated health risks for both animals and humans who consume them. Methodology This study evaluated Hg, methyl-Hg (MeHg) and stable isotopes (δ13C and δ15N) in the muscle, liver and brain of 13 elasmobranch taxa landed by artisanal fisheries on the Western Equatorial Atlantic Ocean. Results The study revealed that Hg concentrations were highest in muscle tissue, whereas the brain exhibited the greatest percentage of MeHg. Significant correlations between Hg levels and body size, as well as between muscle and brain Hg concentrations, were observed in sharks. Stable isotope values indicated dietary and habitat diversity, and a significant correlation between Hg (log10) and δ15N was found. Mercury concentrations exceeded thresholds for harmful effects in ~76% of the analysed taxa and were also detected in embryos. These taxa also surpassed the local consumption limits, highlighting a potential risk. Discussion The results demonstrated bioaccumulation and biomagnification of Hg in the studied taxa. Muscle Hg was a good predictor of brain Hg levels as a result of the significant correlation between these variables. The high proportion of MeHg in the brain indicates rapid transport of Hg to this organ. Observed Hg concentrations in juveniles and adults may affect their health, whereas concentrations in embryos indicate possible transfer of Hg from the mother to the embryos. This study advises caution when consuming various elasmobranchs, depending on the consumer’s weight and meal frequency.
Environmental context Mercury (Hg) is a non-essential metal that can accumulate in aquatic biota, including top predators such as elasmobranchs (sharks and rays) and biomagnifying along the trophic web. This study provides data on Hg total, methylmercury (MeHg) and stable isotopes (δ13C and δ15N) for 13 elasmobranch taxa in the Equatorial Western Atlantic Ocean, relating biological and ecological properties with Hg concentrations and the estimated human consumption risk. Rationale Elasmobranchs widely consume fish, making understanding Hg bioaccumulation crucial. Little is known about Hg distribution in their bodies beyond muscle tissue and the associated health risks for both animals and humans who consume them. Methodology This study evaluated Hg, methyl-Hg (MeHg) and stable isotopes (δ13C and δ15N) in the muscle, liver and brain of 13 elasmobranch taxa landed by artisanal fisheries on the Western Equatorial Atlantic Ocean. Results The study revealed that Hg concentrations were highest in muscle tissue, whereas the brain exhibited the greatest percentage of MeHg. Significant correlations between Hg levels and body size, as well as between muscle and brain Hg concentrations, were observed in sharks. Stable isotope values indicated dietary and habitat diversity, and a significant correlation between Hg (log10) and δ15N was found. Mercury concentrations exceeded thresholds for harmful effects in ~76% of the analysed taxa and were also detected in embryos. These taxa also surpassed the local consumption limits, highlighting a potential risk. Discussion The results demonstrated bioaccumulation and biomagnification of Hg in the studied taxa. Muscle Hg was a good predictor of brain Hg levels as a result of the significant correlation between these variables. The high proportion of MeHg in the brain indicates rapid transport of Hg to this organ. Observed Hg concentrations in juveniles and adults may affect their health, whereas concentrations in embryos indicate possible transfer of Hg from the mother to the embryos. This study advises caution when consuming various elasmobranchs, depending on the consumer’s weight and meal frequency.
Strand monitoring is valuable for identifying human-caused threats to sea turtles but has limitations in fully understanding their overall impact. To address this gap, we conducted a survey to examine sea turtle interactions with longline fisheries, focusing on the types of hooks used for different target fish species. The study aimed to determine the prevalence of sea turtles entangled with hooks in these fisheries and to investigate seasonal and spatial variations in strandings. From August 2015 to December 2020, regular surveys were carried out along 2,013 km, on the South and Southeast coasts of Brazil to monitor sea turtle strandings. Data were collected on the presence and types of hooks, as well as the developmental stages of the affected turtles. The study analyzed spatial and seasonal variations and conducted necropsies to determine causes of death and assess internal damage from fishing gear. A total of 4,631 stranded sea turtles were documented: Caretta caretta, n=3,678, w/hooks=96; Lepidochelys olivacea, n=753, w/hooks=20, and Dermochelys coriacea, n=200, w/hooks= 01. Four types of hooks were identified, with a predominance of “J” hooks typically used in the region to capture dolphinfish, Coryphaena hippurus (72/122 hooks). The most affected developmental stages were large juveniles of C. caretta and L. olivacea. The distribution of hooks differed among the states; “J” hooks targeting C. hippurus on the continental shelf were predominantly found in São Paulo state. In contrast, circular hooks for swordfish (Xiphias gladius) and tuna hooks for tuna (Thunnus spp.), used in offshore fisheries, were more common in southern states. The abundance of “J”, hooks increased during the spring months, aligning with the C. hippurus fishing season. “J” hooks were primarily found in the esophagus of stranded turtles (88/122), indicating that their size and shape facilitate ingestion. Necropsies revealed that 43.1% of deaths (50/116) were due to intestinal lesions caused by hooks, fishing lines, and/or cables. Despite the small relative frequency of individuals found with hooks (117/4631), pelagic longline fisheries, especially those targeting C. hippurus, are a serious threat to sea turtle populations and, therefore, require specific monitoring and mitigating measures. Furthermore, the number of affected individuals may be underestimated since stranding does not represent total mortality at sea.
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