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Elasmobranchs are long-lived predatory fish that show high Hg concentrations generally reflecting environmental levels, notwithstanding they are widely consumed in Brazil increasing Hg exposure to humans. This study reports on Hg concentrations in largely consumed sharks (Rhizoprionodon porosus) and rays (Hypanus guttatus) from the Pernambuco coast, NE Brazil and the risk associated with their consumption. Muscle tissue concentrations of Hg in H. guttatus and R. porosus varied from 40 to 1,020 ng.g-1 w.w. (median = 125; mean = 124 ± 48 ng.g-1 w.w.) in sharks and from 129 to 2,130 ng.g-1 w.w. (median = 976; mean = 919 ± 139 ng.g-1 w.w.) in rays. Concentrations of Hg positively correlated with size in sharks, but not in rays. Concentrations reflect the local environmental contamination of a large urban center and industrial park concentrated in a short extension of mangrove-dominated coastline (50 km) and are higher compared to other Brazilian sites where Hg concentrations in these species have been reported. Sharks had a risk coefficient (HQ) range of 0.04 to 1.1, not surpassing the reference level of exposure. On the other hand, rays' HQ ranged from 0.14 to 2.3, and exceeds the reference level of exposure and suggests adverse effects to consumers.

The smalltail shark, Carcharhinus porosus, was the most abundant elasmobranch species in fisheries off Brazil's northern coast (BNC) in the 1980s, but its population has been declining since the 1990s. For this reason, a demographic analysis is necessary to determine the extent of this decline and the fishing effect on the BNC's population. Therefore, we performed a stochastic demographic analysis of the population in the BNC, and considered its global center of abundance. Smalltail shark specimens (n = 937) were collected with gillnets in Maranhão state, eastern BNC, in the 1980s with sizes ranging between 29.6 and 120.0 cm total length. Most of the individuals (90.6%) caught were juveniles (< 6 years-old), and the mortality and exploitation rates showed that the species was overexploited (92.3% above the fishing mortality corresponding to the population equilibrium threshold). The smalltail shark's biological characteristics, such as slow growth and low fecundity, demonstrate that it is one of the least resilient species among similar sized coastal sharks in the region. All these factors yielded an annual decrease of 28% in the intrinsic population growth rate, resulting in a population decline of more than 90% in only 10 years, and much higher for the current period. This set of features comprising fishing recruitment occurring upon juveniles, overfishing, and intrinsically low resilience make the population unable to sustain fishing pressure and severely hamper biological recruitment, thus causing this drastic population decline. Furthermore, several local extinctions for this species in the northeastern and southeastern regions of Brazil highlight its concerning conservation scenario. Therefore, since similar fisheries characteristics occur throughout its distribution range, C. porosus fits the criteria E of the IUCN Red List for a critically endangered species and urgent conservation measures are needed to prevent its extinction in the near future., Competing Interests: The authors have declared no competing interests.

Simple Summary: The bluntnose sixgill shark, Hexanchus griseus, is a widely distributed species found in all oceans, even if irregularly, inhabiting continental shelves and slopes, islands, and mid-ocean ridges in deep seas. The species is currently classified by the International Union for Conservation of Nature (IUCN) as globally near-threatened, with a decreasing population. Despite some records in Brazil, the known distribution of this species in the Southwestern Atlantic is very patchy and, in some cases, not yet recorded in the world reference literature, such as in northeastern Brazil. This study, therefore, highlights new records for the species in the Tropical Southwestern Atlantic, particularly off the northeastern Brazilian coast. This information is paramount to establishing distribution maps for the species employed in a population status assessment by the IUCN. The bluntnose sixgill shark, Hexanchus griseus, is a widely distributed demersal species found in tropical and temperate waters of the Pacific, Atlantic, and Indian Oceans, inhabiting continental shelves and slopes, islands, and mid-ocean ridges at depths ranging from 200 to 1100 m. In the Southwestern Atlantic, this species has been recorded from northeastern to southern Brazil, Argentina, and Uruguay. Despite this, the known distribution of this species in the Southwestern Atlantic is very patchy and, in some cases, still mostly ignored in the literature, such as in northeastern Brazil. This study, therefore, aimed to report 23 new records of Hexanchus griseus in the Tropical Southwestern Atlantic and highlight the presence of this species off the northeastern Brazilian coast. So far, Hexanchus griseus was officially reported from the Fernando de Noronha Archipelago, Saint Peter and Saint Paul Archipelago, and the state of Ceará along the northeast coast of Brazil. Herein, the known distribution is extended to the continental shelf breaks and upper slopes of other Brazilian states, reinforcing the previously reported occurrence of the species near the Saint Peter and Saint Paul Archipelago. [ABSTRACT FROM AUTHOR]

Ecologically or Biologically Significant Marine Areas (EBSAs) are rare, and highly important sites to the life history of a number of declining shark species are endangered by fishing.The high diversity of sharks caught by fisheries is difficult to monitor due to the scarcity of information on species‐specific biological aspects (growth, maturity and fertility rate).There are two EBSAs off north‐eastern Brazil, where key species are caught, more specifically the oceanic whitetip (Carcharhinus longimanus), mako (Isurus oxyrinchus), blue (Prionace glauca) and silky (Carcharhinus falciformis) sharks. Another 23 species displaying low frequency in catches have also been recorded, many of them considered threatened according to the IUCN Red List and the Brazilian Ministry of Environment.The main purpose of this study was to generate information about shark diversity and demonstrate the role of the two EBSAs in their conservation. After analysing fishing data collected from 2000 to 2011, maps were built to categorize shark species by phases of their ontogenetic development (neonate, young and adult) based on samples of C. falciformis (n = 330), C. longimanus (n = 440), I. oxyrinchus (n = 452) and P. glauca (n = 8,176).Shark stocks comprised mainly juveniles, which raises concerns since they are considered a crucial life stage for the sustainability of shark populations. Catch monitoring also highlighted that several of the species caught are threatened and their catch is either prohibited or limited according to the Brazilian laws and international rules in place.Action plans and enforcement of laws and rules are needed to deliver the protective measures needed for shark species in these EBSAs. [ABSTRACT FROM AUTHOR]

Marginal increment ratio (MIR) analyses were conducted as part of age and growth studies on three coastal/semi-oceanic species, the smalltail shark, Carcharhinus porosus, daggernose shark, Isogomphodon oxyrhynchus and the night shark C. signatus, and two ubiquitous oceanic species, blue shark, Prionace glauca, and whitetip shark, C. longimanus, collected in equatorial areas off Brazil with the aim of establishing the interspecific temporal nature of vertebral band formation. Monthly variations in marginal bands were analyzed using mean MIR on the entire sample as the standard method for all species. Reasons for the inconclusive results regarding these species are critically appraised with respect to three main sources of bias that are associated with marginal increment analysis (MIA). Bias due to insufficient sample sizes may have hampered the analysis for I. oxyrhynchus and C. longimanus due to movements from shallow waters to seamounts for the former species and to extensive migrations for the latter. Bias due to data collection over too long a period is thought to have influenced monthly mean MIR for C. porosus and P. glauca. For the latter, individuals from different age groups lay down rings at different times, making band deposition inconsistent between individuals. Finally, bias due to births occurring over too long a period was the prevalent cause for confounding MIR values among I. oxyrhynchus and C. signatus species, whose birth period lasts several months and leads to different ages within the same cohort. Other approaches used for MIA in C. signatus and P.␣glauca led to distinct times of band formation by age-groups when compared to MIR applied on the entire sample. For the daggernose shark, delays in events related to the reproductive cycle from one year to the next were also found to confound MIR. Requirements for the use of MIR implying a band width that displays a sinusoidal cycle when temporally plotted (month or season) were not fulfilled for any of these species. The method has been of little utility for detecting the periodicity of band deposition among sharks from the tropics. This emphasizes the need for supplying information on the temporal periodicity of pair deposition based on other methods. [ABSTRACT FROM AUTHOR]

Elasmobranch nurseries are habitats where females give birth to their young and juveniles spend their early life history. Hypotheses concerning nurseries suggest that these provide the young a better source of food and protection against predation, however the degree of exposure to predatory risk in nursery areas vary. According to Branstetter hypothesis, slow growing species are either born at relatively large sizes or use protected nursery grounds, whereas faster growing species tend to rely more on growth rates than others factors. Primary nurseries are habitats where parturition occurs and in which the young live for a short time and secondary nurseries are habitats in which juveniles are found after leaving the primary nursery and before reaching maturity. Rhizoprionodon porosus and Carcharhinus acronotus use coastal waters off Caiçara do Norte as both primary and secondary nurseries, while Carcharhinus limbatus makes use of the area as a seasonal primary nursery in late spring and early summer. C. falciformis apparently makes use of the end of inner continental shelf and the outer continental shelf as a primary nursery. Gymnura micrura, Rhinobatos percellens and Narcine brasiliensis makes use of coastal and turbid waters of region as both primary and secondary nurseries throughout the year, while Dasyatis guttata utilizes the area as a primary nursery. Aetobatus narinari and Rhinoptera bonasus, although caught in lesser number, appear to use the region as both primary and secondary nurseries and only primary nursery respectively. Dasyatis marianae (endemic from Northeastern Brazil) may use coastal sandbanks as a primary nursery, while Dasyatis Americana apparently exploits waters about 10 – 20 m in depth with rocky reef substrate only as secondary nursery. There was a measurable degree of temporal and spatial separation among sharks’ species, which may effectively create separate ecological niches, whereas among rays, with the exception of the stingray D. marianae, a spatial and temporal overlaps were observed. The Branstetter’s hypothesis was supported. [ABSTRACT FROM AUTHOR]