Negative metal bioaccumulation impacts on systemic shark health and homeostatic balance

Effects of blood metal(loid) concentrations on genomic damages in sharks

The use of effect biomarkers has contributed to the understanding of the sublethal effects of contaminants on different organisms. However, the analysis of genotoxic markers as an indicator of organism and environmental health in sharks is underexplored. Thus, the present study investigated the relationship between the genomic damage frequency in erythrocytes and metal(loid) concentrations in whole blood of three shark species (Galeocerdo cuvier, Negaprion brevirostris and Ginglymostoma cirratum), taking into account climatic seasonality. The results showed that G. cuvier, an apex predator, presented the highest total erythrocyte genomic damage frequencies together with the highest mean whole blood concentrations of Al, Cd, Cr, Fe, Mn, Ni, Pb and Zn. The shark N. brevirostris also presented high levels of metal(loid), indicating a greater susceptibility to these contaminants in species that preferentially feed on fish. In contrast, G. cirratum, a mesopredator, presented the lowest erythrocyte damage frequencies and whole blood metal(loid) concentrations. The presence of micronuclei was the most responsive biomarker, and Al, As and Zn had an important effect on the genomic damage frequencies for all species evaluated. Zn concentration influenced the binucleated cells frequencies and Al concentration had an effect on the total damage and micronuclei frequencies in G. cuvier and N. brevirostris. Binucleated cells and blebbed nuclei frequencies were affected by As concentration, especially in G. cirratum, while showing a strong and positive correlation with most of the metals analyzed. Nonetheless, baseline levels of metal(loid) blood concentrations and erythrocyte genomic damage frequencies in sharks have not yet been established. Therefore, minimum risk levels of blood contaminants concentrations on the health of these animals have also not been determined. However, the high genomic instability observed in sharks is of concern considering the current health status of these animals, as well as the quality of the environment studied.

Heavy metals and trace minerals in commonly available shark species from North East Arabian Sea: A human health risk perspective

Shark is a seafood commodity that is a good source of minerals and accumulates heavy metals and trace elements through biomagnification, which can pose health risk if taken above the permissible limit. A study was conducted on commonly landed eleven shark species (Scoliodon laticaudus, Rhizopriodon oligolinx, Sphyrna lewini (CR), Carcharhinus macloti, Carcharinus limbatus, Carcharhinus amblyrhynchoides, Carcharhinus sorrah, Carcharinus falciformes(VU), Glaucostegus granulatus, Chiloscyllium arabicum, Loxodon macrorhinus) and analyzed for their heavy metal content, Hazard Index, Total Hazard Quotient, Metal Pollution Index, and also calculated the health risk associated with the consumption. Most of the heavy metals and trace minerals were found to be within the acceptable limit. The Targeted Hazard Quotient (THQ) and the Hazard Index (HI) of all the species except two were less than 1 (HI ≤ 1.0). The Metal Pollution Index (MPI) is showing either no impact or very low contamination. An overall study on hazard identification and health risk characterization in terms of heavy metals shows contamination of some heavy metals in sharks, but there is no potential human health risk associated with consumption.

Multispecies and multibiomarker assessment of fish health from Iguaçu River reservoir, Southern Brazil

This study investigated the impact of micropollutants on fish health from Segredo hydroelectric reservoir (HRS) along the Iguaçu River, Southern Brazil, contaminated by urban, industrial, and agricultural activities. This is the first comprehensive study assessment in the river after the severe drought in the 2020s in three fish species from different trophic levels Astyanax spp. (water column depth/omnivorous), Hypostomus commersoni (demersal/herbivorous), and Pimelodus maculatus (demersal/omnivorous). Animals, water, and sediment samples were collected from three distinct sites within the reservoir: Floresta (upstream), Iratim (middle), and Station (downstream). The chemical analysis revealed elevated concentrations of metals (Al, Cu, Fe) and the metalloid As in water, or Cu, Zn, and As in sediment, surpassing Brazilian regulatory limits, while the organic pollutants as DDT, PAHs, PCBs, and PBDEs were found under the Brazilian regulatory limits. The metal bioaccumulation was higher in gills with no significant differences among sites. The species Astyanax spp. and H. commersoni displayed variations in hepatosomatic index (HSI) and P. maculatus in the condition factor index (K) between sites, while adverse effects due to micropollutants bioaccumulation were observed by biochemical, genotoxic, and histopathological biomarkers. The principal component analysis and integrated biomarker response highlighted the upstream site Floresta as particularly inhospitable for biota, with distinctions based on trophic level. Consequently, this multifaceted approach, encompassing both fish biomarkers and chemical analyses, furnishes valuable insights into the potential toxic repercussions of micropollutant exposure. These findings offer crucial data for guiding management and conservation endeavors in the Iguaçu River.

Heavy metal and trace element concentrations in the blood of scalloped hammerhead sharks (Sphyrna lewini) from La Paz Bay, México

Sharks are particularly susceptible to bioaccumulation due to their life history characteristics and trophic position within marine ecosystems. Despite this, studies of bioaccumulation cover only a small proportion of extant species. In this study we report concentrations of trace elements and heavy metals in blood samples of Sphyrna lewini for the first time. We report high concentrations of several trace elements and heavy metals, with concentrations of some elements exceeding the limit determined safe for human consumption. High elemental concentrations may reflect biochemical differences between blood plasma and other tissues; however, they may also be symptomatic of high levels of exposure triggered by anthropogenic activities. We also provide evidence of elemental accumulation through ontogeny, the nature of which differs from that previously reported. Ultimately, this baseline study increases our understanding of interspecific and intraspecific variation in bioaccumulation and ecotoxicology in elasmobranchs which may prove important in ensuring adequate management.

Heavy metal concentrations in sharks, rays and chimaeras from the western Mediterranean Sea

The potential bioaccumulation of pollutants, such as heavy metals, may pose a threat to the western Mediterranean chondrichthyans and human consumers. Therefore, the first extensive assessment of cadmium (Cd), lead (Pb), and copper (Cu) concentrations in the muscle tissue of 17 species of sharks, rays, and chimaeras in this region was conducted via Microwave Assisted Extraction (MAE) and Graphite Furnace Atomic Absorption Spectrometry (GFAAS). Significant differences between species were observed, particularly related to the rabbit fish (Chimaera monstrosa) and the velvet belly lantern shark (Etmopterus spinax), which exceeded the European Union (EU) Commission Regulation 2023/915 threshold of Cd. Overall, heavy metal concentrations correlated negatively with size and trophic level but positively with depth. Although the consumption of these species may entail minimal risk to adult humans, caution is advised, especially for children. These findings are important due to the widespread consumption of chondrichthyans in many western Mediterranean regions.

Ecotoxicology applied to conservation: Potential negative metal and metalloid contamination effects on the homeostatic balance of the critically endangered Brazilian guitarfish, Pseudobatos horkelii (Elasmobranchii: Rhinobatidae)

Metal contamination poses a significant threat to elasmobranchs, underscoring the need for targeted conservation approaches. The critically endangered Brazilian guitarfish, Pseudobatos horkelii, confronts an array of challenges, notably overexploitation, putting its survival at risk. Our study investigated the potential toxicity arising from arsenic (As), cadmium (Cd), mercury (Hg), and lead (Pb) contamination across various adult guitarfish tissues from southeastern Brazil. Serological stress indicators, nutritional metabolites, and creatinine, an organ function marker, were also assessed, and Selenium (Se) levels were also investigated for possible protective effects. Our investigation unveiled significant correlations between metal concentrations and the determined physiological markers, shedding light on potential adverse effects. Remarkably, six correlations were indicative of how Hg and Pb negatively impact hepatic metabolite assimilation, while As was shown to influence renal phosphorus dynamics, Cd to affect rectal gland phosphorus regulation, and Pb to influence creatinine production in muscle tissue. Furthermore, Se demonstrated protective properties against Cd, Hg, and Pb, suggesting a role in alleviating the toxicity of these elements. Despite probable protective Se influences, the detected elemental interactions still suggest potential for organ impairment. These findings gain heightened significance within the context of the cumulative stressors faced by the Brazilian guitarfish, with metal contamination exhibiting the capacity to erode this species resilience against both anthropogenic and environmental pressures, thereby disrupting systemic equilibrium and jeopardizing wild populations. By investigating the intricate balance between metal accumulation and physiological consequences, our study contributes with crucial insights into potential conservation strategy formulations towards pollution for this critically endangered elasmobranch species.

A systematic review on polycyclic aromatic hydrocarbon contamination in elasmobranchs and associated human health risks

Polycyclic aromatic hydrocarbon (PAH) contamination is ubiquitous and comprises a significant worldwide concern in ecological and Public Health frameworks. Many aquatic biota representatives have been reported as contaminated by these toxic compounds, including one of the most threatened vertebrate groups, elasmobranchs (sharks and rays). Although elasmobranchs play important ecological roles and provide significant ecosystem services, they are highly consumed and comprise a cheap source of protein for humans globally. Studies concerning elasmobranch PAH contamination are, however, notably lacking. A systematic review was, thus, conducted herein to assess PAH elasmobranch contamination and discuss potential human health risks following the Preferred Reporting Item Statement Guidelines for Systematic Reviews and Meta-analyses (PRISMA) guidelines applying the Population (P), Intervention (I), Comparison I, and Outcome (O) (PICO) strategy. A total of 86 published papers were retrieved by this method and analyzed. Only nine studies of this total concerned PAH elasmobranch contamination, assessed in 10 shark species and one ray species, with only one study calculating human health risks. A significant knowledge gap is, thus, noted for this subject, indicating the need to monitor PAH elasmobranch contamination in consumed shark and ray species worldwide.

The fate of plastic-wearing sharks: Entanglement of an iconic top predator in marine debris

Plastic waste is currently a major threat to marine ecosystems, and the ever-growing production of plastic materials suggests that this scenario will not change soon. Understanding cryptic effects of plastic debris on keystone marine species is warranted to address ecosystem-level impacts caused by plastic pollution. This study reports on plastic entanglement in top predator tiger sharks, Galeocerdo cuvier, from the western South Atlantic Ocean. Circular plastic straps produced severe trauma in 3 % of all tiger sharks sampled and led to abnormal anatomical development, indicating worrisome incidence and consequences of plastic entanglement in this species. Removing the plastic strap from one shark which had been entangled for at least 9 months was probably the cause for the shark having experienced post-release mortality. This suggests that, in some circumstances, strap removal is not effective to promote the survival of entangled sharks. Eliminating the circular integrity of plastic materials at first use should contribute to mitigate some of the impacts of plastic pollution on marine megafauna since this shape might be determinant in the process of shark entanglement.

Tissue metal concentrations and antioxidant enzyme activity in western north Atlantic white sharks (Carcharodon carcharias)

Anthropogenic practices have increased metal contamination in marine ecosystems. Most sharks have long lifespans, occupy an important ecological position at the top of marine food webs, and can accumulate metals. However, reference levels of metal contaminants in the tissues of sharks, particularly, apex predators such as the white shark (Carcharodon carcharias), are lacking. In this study, concentrations of copper (Cu), cadmium (Cd), nickel (Ni), lead (Pb), silver (Ag), and zinc (Zn) were measured in the muscle tissue of white (n = 42) and tiger (Galeocerdo cuvier; n = 3) sharks. Metal exposure in various species, including sharks, has been correlated with increased oxidative stress. Therefore, the main objectives of this study were to assess metal accumulation and antioxidant enzyme activity (superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx)) in the muscle tissue of the population of white sharks and tiger sharks inhabiting the Western North Atlantic. The measured parameters were qualitatively compared between species. The small sample size of tiger sharks (collected from only one site) limited statistical analyses, therefore, white sharks were the primary focus of this study. Differences in tissue metal (Cu, Cd, Ni, and Zn) concentrations and antioxidant enzyme activities were detected based on collection site, with significant positive correlations between Cd and enzymes, SOD and CAT, and Zn and enzymes, SOD and GPx in C. carcharias. Differences in Ni concentration were detected based on sex, with females having higher Ni levels. Additionally, plasma osmolality was not correlated with tissue metal concentrations; however, osmolality decreased with increasing length in C. carcharias. This study is the first to report baseline levels of Cu, Zn, Cd, Ni, Ag, and Pb in muscle of North Atlantic white sharks and provides new insights into oxidative stress responses of these sensitive species to metal contaminants.

Comparative genomic damage among three shark species with different habits: Sublethal impacts of human origin in a protected island environment in the South Atlantic

Elasmobranchs can bioaccumulate and biomagnify pollutants. However, few studies are directed to the effects of pollutants on the health of these animals, and in most cases, are limited to the analysis of biochemical markers. Thus, the incidence of genomic damage among shark species inhabiting a protected ocean island in the South Atlantic was investigated in association with the analysis of pollutants in seawater sample. High levels of genomic damage were identified, especially in Negaprion brevirostris and Galeocerdo cuvier, in addition to interspecific variations that may be related to characteristics such as animal size, metabolism and habits. High concentrations of Surfactants were observed in seawater sample, in addition to low concentrations of Cadmium, Lead, Copper, Chromium, Zinc, Manganese, and Mercury. The results evidenced the potential of shark species as a bioindicator of environmental quality and allowed assessing the anthropic impact on the archipelago, which currently drives its economy through tourism.

Exploring the Impact of Contaminants of Emerging Concern on Fish and Invertebrates Physiology in the Mediterranean Sea

In this historical context, the Mediterranean Sea faces an increasing threat from emerging pollutants such as pharmaceuticals, personal care products, heavy metals, pesticides and microplastics, which pose a serious risk to the environment and human health. In this regard, aquatic invertebrates and fish are particularly vulnerable to the toxic effects of these pollutants, and several species have been identified as bio-indicators for their detection. Among these, bivalve molluscs and elasmobranchs are now widely used as bio-indicators to accurately assess the effects of contaminants. The study focuses on the catshark Scyliorhinus canicular and on the Mediterranean mussel Mytilus galloprovincialis. The first one is a useful indicator of localised contamination levels due to its exposure to pollutants that accumulate on the seabed. Moreover, it has a high trophic position and plays an important role in the Mediterranean Sea ecosystem. The bivalve mollusc Mytilus galloprovincialis, on the other hand, being a filter-feeding organism, can acquire and bioaccumulate foreign particles present in its environment. Additionally, because it is also a species of commercial interest, it has a direct impact on human health. In conclusion, the increasing presence of emerging pollutants in the Mediterranean Sea is a serious issue that requires immediate attention. Bivalve molluscs and elasmobranchs are two examples of bio-indicators that must be used to precisely determine the effects of these pollutants on the marine ecosystem and human health.

Impacts of water pollutants on chondrichthyans species from South America: A review

This is the first research that extensively compiles all the available scientific literature on the presence of trace metals (TMs), persistent organic pollutants (POPs), and plastic debris in Chondrichthyan species inhabiting South America (including the Atlantic and Pacific Oceans), providing an insight into Chondrichthyans as bioindicators of pollutants as well as the impacts of pollutant exposure on the organisms. Seventy-three studies were published in South America between 1986 and 2022. While 68.5% focused on TMs, 17.8% on POPs, and 9.6% on plastic debris. Brazil and Argentina were at the top in terms of the number of publications; however, there is an absence of information regarding pollutants for Chondrichthyans in Venezuela, Guyana, and French Guiana. Of the 65 Chondrichthyan species reported, 98.5% belong to the Elasmobranch group, and 1.5% from the Holocephalans. Most studies focused on Chondrichthyans of economic importance, and the most analyzed organs were the muscle and liver. There is a lack of studies on Chondrichthyan species with low economic value and critical conservation status. Due to their ecological relevance, distribution, accessibility, high trophic position, capacity to accumulate high levels of pollutants, and the number of studies published, Prionace glauca and Mustelus schmitii seem to be adequate to serve as bioindicators. For TMs, POPs, and plastic debris there is a lack of studies focusing on the pollutant levels as well as their effect on Chondrichthyans. Future research reporting TMs, POPs, and plastic debris occurrences in Chondrichthyan species are required in order to increase the scarce databases about pollutants in this group, with a clear need for further research on the responses of chondrichthyans to pollutants, as well as making inferences about the potential risks to the ecosystems and human health.

Contamination by Trace Elements and Oxidative Stress in the Skeletal Muscle of Scyliorhinus canicula from the Central Tyrrhenian Sea

Marine pollution, due to the regular discharge of contaminants by various anthropogenic sources, is a growing problem that imposes detrimental influences on natural species. Sharks, because of a diet based on smaller polluted animals, are exposed to the risk of water contamination and the subsequent bioaccumulation and biomagnification. Trace elements are very diffuse water pollutants and able to induce oxidative stress in a variety of marine organisms. However, to date, studies on sharks are rather scarce and often limited to mercury. In this context, the present study aimed to analyze the accumulation of trace elements and their putative correlation with the onset of an oxidative status in the muscle of the lesser spotted dogfish Scyliorhinus canicula, from the Central Mediterranean Sea. Ecotoxicological analysis detected the presence of Pb, As, Cd, Mn, Zn, Ni, Cu, and Fe; no significant differences were observed between sexes, while a negative correlation was found between Pb and animal length. Analysis of oxidative stress markers showed either positive or negative correlation with respect to the presence of trace elements. Lipid peroxidation (TBARS) positively correlated with Zn, Ni, and Fe; SOD enzyme activity negatively correlated with Cu and Ni; LDH was negatively correlated with Fe and positively correlated with Pb. Moreover, positive correlations between the leukocyte count and Mn and Zn, as well as with LDH activity, were also observed. The data suggested that, in sharks, trace elements accumulation may affect oxidant and antioxidant processes with important outcomes for their physiology and health.

Almost nothing is known about the tiger shark in South Atlantic waters

The tiger shark (Galeocerdo cuvier) has been relatively well assessed concerning biology and ecology aspects in both Atlantic and Pacific North America and in Caribbean waters. The amount of data in these regions has led to the species protection under capture quotas and with the creation of sanctuaries. The reality in developing countries, however, is the exact opposite, with scarce information on the species in the southern hemisphere, namely South American and African waters. In these regions, protection measures are insufficient, and studies on tiger shark biology and ecology are scarce, significantly hindering conservation and management efforts. Thus, the aim of this study was to compile scientific literature on the tiger shark in the South Atlantic and discuss the impact of these data (or lack thereof) distributed within a total of ten research categories for guiding management plans. In total, 41 scientific publications on different G. cuvier biology and ecology aspects were obtained. The most studied topics were Feeding Ecology (n = 12), followed by Human Interactions (n = 8), and Movements and Migration (n = 7). Northeastern Brazil (Southwest Atlantic) was the most researched area, probably due to the higher coastal abundance of tiger sharks in this area, alongside a high number of recorded attacks, justifying funding for studies in the region. No studies carried out in other South American or African countries were found. It is important to mention that even though some research topics are relatively well covered, a severe knowledge gap is noted for risk assessments and fisheries management, with a proposition for the implementation of sanctuaries noted. This is, however, particularly worrisome, as the South Atlantic is mostly unexplored in this regard for tiger sharks. It is also important to note how different the attention given to this species is in the North Atlantic when compared to the South region. Lastly, we highlight that the existence of sub-populations, the lack of migratory corridors geographically connecting distinct areas used by the species, and the lack of fisheries statistics on tiger shark landings, all increase the vulnerability of this species in the South Atlantic.

Determination of metals in estuarine fishes in a metropolitan region of the coastal zone of the Brazilian Amazon

The aim of the present study was to determine concentrations of cadmium, copper, chromium, manganese and iron in fishes in the São Marcos (SMB), São Jose (SJB) and Arraial (AB) Bays. Metal concentrations were determined using inductively coupled plasma optical emission spectrometry. Mean Cd and Cr levels were above the permissible limits set by different international or national guidelines in all three bays, whereas copper levels were well below the maximum acceptable limit. High concentrations of iron were found in all species analyzed, whereas high concentrations of manganese were found, especially in specimens caught in SJB. Spatial analysis indicated significant differences among the elements investigated. Copper was correlated more with SMB and AB as well as the species Macrodon ancylodon (carnivore) and Sciades herzbergii (omnivore). Cadmium and iron were strongly associated with AB and SJB, while manganese was only associated with SJB, mainly in carnivorous and herbivorous species.

Trace elements in edible tissues of elasmobranchs from the North Aegean Sea (Eastern Mediterranean) and potential risks from consumption

Trace elements have the potential to bioaccumulate in marine organisms and to biomagnify towards the upper levels of marine trophic webs, resulting in a range of negative effects on organisms. Elasmobranchs are highly susceptible to bioaccumulation of trace metals, while their consumption by humans is increasing worldwide. Therefore, it is important to monitor the trace metal content in the edible tissues of elasmobranchs. This work reveals the content of 12 trace metals in the edible tissues of 10 elasmobranch species caught in Greek waters. Levels above the permissible limits for Hg and Pb were found in some species, while analysis of the lifetime consumption risk for adults and children using the Target Hazard Quotient (THQ), revealed a high risk for two of the most toxic substances on the priority list for substances, namely As and Hg. These are preliminary results, and further research is required to understand better the issue.

First report on metal and metalloid contamination of Ampullae of Lorenzini in sharks: A case study employing the Brazilian sharpnose shark Rhizoprionodon lalandii from Southeastern Brazil as an ecotoxicological model

Metal contamination has never been assessed in Ampullae of Lorenzini. This study employed Rhizoprionodon lalandii, as an ecotoxicological model to investigate potential metal accumulation in Ampullae of Lorenzini jelly. No differences between sexes were observed regarding jelly metal concentrations at Rio das Ostras (RJ) or Santos (SP). Statistically significant correlations were noted between total lengths (TL) and condition factors and several metals at both sampling sites, demonstrating the potential for Chondrichthyan sensory capacity disruption and possible effects on foraging success. Maternal metal transfer to Ampullae jelly was confirmed. Rhizoprionodon lalandii is thus, a good model to assess Ampullae of Lorenzini contamination, as this electrosensory organ seems to be highly vulnerable to metal contamination.

Subcellular metal partitioning as a novel tool in ecotoxicological elasmobranch assessments: The case of lesser numbfish (Narcine brasiliensis) affected by the Mariana dam disaster in Southeastern Brazil

This study comprises a novel report on subcellular metal partitioning and metallothionein (MT) metal detoxification efforts in lesser numbfish (Narcine brasiliensis) electric ray specimens, as well as the first assessment on MT contents in any ray electric organ. Individuals sampled from an area in Southeastern Brazil affected by the Mariana dam rupture disaster were assessed concerning subcellular metal partitioning and MT metal-detoxification in the liver, gonads, electric organ and muscle of both adults and embryos. Yolk was also assessed when available. Relative total and heat-stable (bioavailable) metal and metalloid comparisons between adults and embryos in different developmental stages demonstrates maternal transfer of both total and bioavailable metals and significant MT associations demonstrate the detoxification of As, Ag, Mn, Ni, Cd, Co, Cu, Se and V through this biochemical pathway. Our findings expand the lacking ecotoxicological assessments for this near-threatened species and indicates significant ecological concerns, warranting further biomonitoring efforts.

Elasmobranchs as bioindicators of pollution in the marine environment

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 in relevant 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 than 12 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., heat shock 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., lactate dehydrogenase, lactate, and cholinesterases), and histopathological and morphologic biomarkers (e.g., tissue lesions and gross indices).

Nurse sharks, space rockets and cargo ships: Metals and oxidative stress in a benthic, resident and large-sized mesopredator, Ginglymostoma cirratum

It is widely recognized that apex predators, such as large sharks with highly migratory behavior, are particularly vulnerable to pollution, mainly due to biomagnification processes. However, in highly impacted areas, mesopredator sharks with resident behavior can be as vulnerable as apex sharks. In this context, this study evaluated cadmium (Cd), mercury (Hg), lead (Pb), and rubidium (Rb) concentrations, as well as the potentially protective effects of selenium (Se) and the behavior of two non-enzymatic biomarkers, metallothionein (MT) and reduced glutathione (GSH), employing the Atlantic nurse shark Ginglymostoma cirratum as a study model and compared the results with other resident benthic sharks, as well as highly mobile apex sharks. Muscle tissue samples from 28 nurse sharks opportunistically sampled from the Brazilian Amazon Coast were analyzed. Lower metal concentrations were observed for Pb, Rb and Se in the rainy season, while statistically significant correlations between metals were observed only between Hg and Cd and Pb and Se. Molar ratio calculations indicate potential protective Se effects against Pb, but not against Cd and Hg. No associations between MT and the determined metals were observed, indicating a lack of detoxification processes via the MT detoxification route. The same was noted for GSH, indicating no induction of this primary cellular antioxidant defense. Our results indicate that benthic/mesopredator sharks with resident behavior are, in fact, as impacted as highly mobile apex predators, with the traditional detoxification pathways seemingly inefficient for the investigated species. Moreover, considering the studied population and other literature data, pollution should be listed as a threat to the species in future risk assessments.

Research trends on elasmobranchs from the Brazilian Amazon Coast: a four-decade review

Abstract: Elasmobranchs exhibit the biggest population declines among vertebrates, being considered one of the groups with the highest risk of extinction. The Brazilian Amazon Coast (BAC) is considered a priority area for elasmobranch conservation, as many species are endemic to the region, and most of them are threatened with extinction. The present study made a scientometric analysis using the IRAMUTEQ method (Interface de R pour les Analyses Multidimensionnelles de Textes et de Questionnaires) to evaluate the trends of research with elasmobranchs in BAC in the last four decades. Ten research trends were identified, highlighting “Biodiversity”, “Reproduction”, “Trophic Ecology” and “Conservation”. However, most of the publications found are aimed at understanding the diversity and abundance of species in the region, with the number of studies focused on reproduction, feeding and other aspects of the biology and ecology of elasmobranchs in the BAC being less expressive. Although the research area “Conservation” stood out in the search, the amount of relevant information so that management and conservation measures can be implemented is still low. Lastly, despite following the global trend of studies with elasmobranchs between 2000 and 2010, investigations into the BAC need to advance, especially considering the poor level of basic information on most species (Biology and population dynamics) and the incomplete knowledge of specific composition of elasmobranch species in the entire area, aspects relevant to conservation and more applied studies that rely on more recent methodologies and technologies.