Search

Occurrence of multiple whitetip reef sharks Triaenodon obesus in the Atlantic Ocean is reported for the first time from near a sunken ferry off the Paraná coast in south‐eastern Brazil. This occurrence is hypothesized to have been caused by either a human introduction or a remarkably long oceanic displacement. [ABSTRACT FROM AUTHOR]

Amidst global declines in elasmobranch populations resulting predominantly from overfishing, the need to gather data regarding shark ecology is greater than ever. Many species remain data deficient or at risk of going extinct before sufficient conservation measures can be applied. In this review, we summarise existing knowledge regarding the biology and ecology of the Pacific sharpnose shark Rhizoprionodon longurio (Jordan & Hilbert, 1882), a small‐bodied carcharhinid shark found in coastal waters of the Eastern Tropical Pacific Ocean that is of both commercial and ecological importance. We compare ecological parameters of this species with its closest extant relatives and identify major knowledge gaps and avenues for future research. In particular, additional studies investigating the behavioural and sensory ecology, as well as potential migratory patterns of the species are needed. Such studies will not only improve our understanding of R. longurio, but provide insight into the extent to which the numerous studies performed on a close relative—Rhizoprionodon terraenovae—provide an accurate representation of the biology and ecology of Rhizoprionodon and carcharhinids more generally. [ABSTRACT FROM AUTHOR]

Sharks and rays evolved 450 million years ago, during the Late Ordovician Period. However, during the modern Anthropocene, shark populations have declined at considerable rates, and recent global assessments indicate about one in three species is threatened with extinction. A notable reason for this elevated extinction risk is overfishing linked to increased demand for shark fins and other products. Here, we review multiple dimensions of consuming shark products, ranging from stock sustainability, product (mis)labelling and trade, the human health implications of consuming shark products, and illegal, unreported and unregulated fishing and slavery and labour abuses in the fishing industry. We conclude that traceability and increased transparency in seafood supply chains is essential to overcome obstacles to consumption of sustainable, ethical and healthy shark products. We also provide a decision tree outlining steps in consumer choice that would foster such consumption. Our aim is to provide a holistic view on issues concerning the consumption of shark products that will help policymakers, the public, management and law enforcement agencies to advocate for ecologically‐ and ethically sustainable consumption of shark products and thereby empower the general public to make informed decisions on which shark products they consume. [ABSTRACT FROM AUTHOR]

Bull shark (Carcharhinus leucas) is a near‐threatened elasmobranch species capable of moving between the fresh and salty waters of tropical and subtropical coastal areas, for which we still lack important ecological information. During their first years of life, bull sharks use estuarine systems as nursery areas, making them highly susceptible to environmental and anthropogenic pressures. We studied the trophic ecology of juveniles found in the Coyote estuary, a potential nursery area in Costa Rica, to understand the potential impact of further bull shark declines and gain knowledge that could aid in their conservation. We analysed the trophic ecology of juvenile bull sharks [81–103 cm total length (TL)] in the Coyote estuary, Costa Rica, using stable isotopes of δ15N and δ13C. Since one problem using this technique in juveniles is the confounding effect of the maternal signature, we sampled different tissues (muscle and plasma), verified the status of the shark's umbilical scar and identified the size at which the isotope signature is a result of the animal's current diet. The isotopic values of the muscle tissue reflected the maternal isotopic signature. In contrast, plasma values reflected the diet of juvenile bull sharks >95 cm TL and with a closed umbilical scar. Juvenile bull sharks fed primarily on teleost fishes of the order Anguilliformes and Siluriformes, and have a high trophic position (≥4.0) in the Coyote estuary. Our findings suggest that this estuary is an important feeding site for juvenile bull sharks of the Pacific of Costa Rica. Thus, the protection of essential habitats such as the Coyote estuary will benefit not only bull shark conservation, but also the conservation of an array of fish species that also use this habitat as a rookery, many of which are of commercial interest. [ABSTRACT FROM AUTHOR]

Trophic ecology studies on predator–prey interactions reveal insights into ecological communities and help understand a species' role in the food web by contributing to improved fisheries management and conservation capabilities. Understanding the ecological role of overexploited and endangered predators is essential to deciphering how their feeding behaviour influences food web dynamics. In this study, the authors investigated the feeding behaviour of the common and IUCN‐listed Near Threatened (NT) thornback ray Raja clavata, using carbon and nitrogen stable isotope and stomach content analysis (SCA). It has recently suffered an 87% decline in reported catches from the Sea of Marmara within the last decade. These results show that thornback ray mainly feeds on teleost species, except in summer, with both methods showing this species changes its diet ontogenetically by SCA. This ontogenetic diet shift was at lengths 40–50 cm by changing group preferences from Crustacea to Teleostei. MixSIAR results showed that both adult and juvenile individuals of R. clavata feed mainly on the crustaceans, but the contribution of teleosts represented by Trachurus sp. was very low (<15%). The trophic position increased total length and was higher than other batoid species in the Sea of Marmara. [ABSTRACT FROM AUTHOR]

Increasing fishing pressure has negatively impacted elasmobranch populations globally. Despite high levels of historical and current fishing pressure, the Bay of Bengal region remains data‐poor. Focusing on Bangladesh, we conducted a socio‐ecological study to characterize elasmobranch fisheries and evaluate their impact on threatened species. The results demonstrate that several globally threatened elasmobranch species are frequently captured, and some of them have experienced substantial population declines (e.g., wedgefishes, sawfishes, large carcharhinid sharks) over the past decade. A decrease in elasmobranch diversity, abundance, and size of caught specimens was also reported, which was attributed to increased fishing intensity, destructive practices (e.g., bottom trawling), and an accessible elasmobranch market. While catch and trade of more than 90 elasmobranchs are regulated under Bangladesh's law, non‐compliance is widespread. Likely causes include a dearth of awareness, practical alternative livelihoods, and technical facilities, and the complex nature of the fisheries. Encouraging and facilitating the engagement of fishers in science (data collection), local governance (policy‐making), and field implementation (bycatch mitigation) is vital. These interventions must be rooted in sustainable approaches and co‐designed with fishers, with appropriate training available. Development of this work through enhanced engagement with fishers has the potential to transform the elasmobranch fishery situation in Bangladesh and could be used as a model for data‐poor regions. [ABSTRACT FROM AUTHOR]

Giant guitarfishes (Glaucostegidae) and wedgefishes (Rhinidae) are some of the most threatened marine taxa in the world, with 15 of the 16 known species exhibiting global population declines and categorized as Critically Endangered according to the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. The recent inclusion of all species in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) necessitates more rigorous enforcement by regulatory authorities.Challenges in regulating the trade of giant guitarfish and wedgefish products due to difficulties in visual identification of processed products and labelling issues impede enforcement. The aim of this study is to characterize the diversity and origins of associated traded products that were commercially available in Singapore, one of the world's top importers and re‐exporters of shark and ray products.A total of 176 samples of elasmobranch products were obtained between June and December 2019 from fishery ports and various retailers in Singapore. By applying cytochrome c oxidase subunit I gene barcoding, 31 elasmobranch species were detected, with 55% of the species considered threatened (Critically Endangered, Endangered, or Vulnerable) based on the IUCN Red List and 35% of species listed in CITES Appendix II. Four species of giant guitarfishes and wedgefishes were commercially available to consumers in fresh forms of whole fish, fillet, and fin, as well as dried and cooked meats.DNA barcoding has proven to be an effective tool for identifying elasmobranch products that are impossible to recognize visually and would aid enforcement of CITES trade regulations. This work underscores the urgent need to step up enforcement of marine wildlife regulations and draw public attention to the elasmobranch trade. [ABSTRACT FROM AUTHOR]

Animal dietary information provides the foundation for understanding trophic relationships, which is essential for ecosystem management. Yet, in marine systems, high‐resolution diet reconstruction tools are currently under‐developed. This is particularly pertinent for large marine vertebrates, for which direct foraging behaviour is difficult or impossible to observe and, due to their conservation status, the collection of stomach contents at adequate sample sizes is frequently impossible. Consequently, the diets of many groups, such as sharks, have largely remained unresolved. To address this knowledge gap, we applied metabarcoding to prey DNA in faecal residues (fDNA) collected on cotton swabs from the inside of a shark's cloaca. We used a previously published primer set targeting a small section of the 12S rRNA mitochondrial gene to amplify teleost prey species DNA. We tested the utility of this method in a controlled feeding experiment with captive juvenile lemon sharks (Negaprion brevirostris) and on free‐ranging juvenile bull sharks (Carcharhinus leucas). In the captive trial, we successfully isolated and correctly identified teleost prey DNA without incurring environmental DNA contamination from the surrounding seawater. In the field, we were able to reconstruct high‐resolution teleost dietary information from juvenile C. leucas fDNA that was generally consistent with expectations based on published diet studies of this species. While further investigation is needed to validate the method for larger sharks and other species, it is expected to be broadly applicable to aquatic vertebrates and provides an opportunity to advance our understanding of trophic interactions in marine and freshwater systems. [ABSTRACT FROM AUTHOR]

Sharks and rays caught by a small-scale fisheries in the western equatorial Atlantic Keywords: artisanal fisheries; Chondrichthyes; conservation; elasmobranch; endangered species EN artisanal fisheries Chondrichthyes conservation elasmobranch endangered species 830 833 4 12/21/20 20201201 NES 201201 INTRODUCTION The more than 1,100 known species of sharks and rays (Weigmann, 2016) are important trophic components of marine ecosystems. DISCUSSION This is the first study to use systematic monitoring of fisheries landings to describe the coastal fauna of elasmobranchs for the Ceará state and one of few for northeastern Brazil. The most captured and landed elasmobranch species at the Mucuripe embayment, I H. americanus i and I R. porosus i , are currently considered Data Deficient in Brazil (ICMBio, 2016). [Extracted from the article]

This study aimed to characterize morphological aspects related to abortion through a non‐lethal approach in the shortnose guitarfish Zapteryx brevirostris, an endemic and threatened species commonly caught by artisanal fisheries. Two females with signs of abortion and one female exhibiting external signs of pregnancy were purchased alive at a fish market during the period when this species has developing embryos in southern Brazil. Scans were conducted using a portable ultrasound. Females with signs of abortion revealed an absence of embryos despite having a similar morphology of the uterus when compared to the pregnant female. Examination of the pregnant female revealed the presence of two embryos, measuring c. 100 mm, each detected through their midline. This study presents new data on uterine macromorphology following successive abortive events in a viviparous elasmobranch species and validates ultrasonography as a diagnostic tool for the species. Ultrasonography is an effective, non‐lethal and less‐invasive methodology that is recommended for use in future studies of abortion and other reproductive events in elasmobranchs. [ABSTRACT FROM AUTHOR]

The reproductive biology of Urotrygon microphthalmum was studied based on specimens caught as by-catch in shrimp ( Litopenaeus schmitti, Xiphopenaeus kroyeri, Farfantepenaeus subtilis and Farfantepenaeus brasiliensis) fishing operations between March 2010 and March 2012 on the coast of Pernambuco, Brazil. Females reached a larger total length ( LT) and total body mass ( MT) (298 mm and 148 g) than males (250 mm and 90 g). Length at maturity was estimated to be 188 and 199 mm LT for males and females. Uterine fecundity ranged from one to four embryos (mean ± s.d.: 1·85 ± 0·45). Size at birth was estimated to be 105 mm LT. Gestation lasted between 4 and 5 months. The reproductive cycle of U. microphthalmum is hypothesized to be asynchronous and biannual. [ABSTRACT FROM AUTHOR]

The diet and diel feeding behaviour of the banded guitarfish Zapteryx xyster were examined along the Pacific coast of Costa Rica. A sample of 235 stomachs was collected between March 2010 and December 2011 as part of an ongoing shrimp-trawl by-catch monitoring programme. Samples from multiple day and night periods allowed testing the hypothesis that Z. xyster is more active at night, thus increasing the amount of food intake during night-time. Overall, shrimps (52·3% prey-specific index of relative importance, PSIRI i) and teleosts (27·2% PSIRI i) were the most important prey categories. Juveniles fed primarily on smaller shrimps ( Solenocera spp.), while adults shifted to larger prey. The amount of food consumed (as % of bodymass) by juvenile and adult Z. xyster increased significantly between 0400 and 1200 hours, while the proportion of empty stomachs decreased during the same time interval. These findings contradict the hypothesis that Z. xyster is more active and feeds at night. The study also revealed that Z. xyster, particularly juveniles, forage on several shrimp species and overlap spatially with the Costa Rican bottom-trawl fisheries. This has important management and conservation implications as Z. xyster may be experiencing high by-catch rates, and because of their life history is presumed to be vulnerable to intense levels of exploitation. [ABSTRACT FROM AUTHOR]