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Depredation (the partial or complete removal of a hooked species by a non‐target species) is a human–wildlife conflict as old as humans and the sea. In some ways, depredation is no different today than it was a century ago. But in many ways, this conflict has become more complicated. Following three decades of successful management, some US shark populations have begun to rebuild. However, many anglers attribute perceived increases in shark depredation to management measures, claiming they have led to 'overpopulation' of sharks and/or learned behaviour by sharks. We investigated whether these factors could explain the reported increases in depredation. Based on fishery‐independent surveys, neither shark population increases nor learned behaviour by sharks is evident. However, increases in angler effort provide an alternative explanation that is not often considered. While far from a smoking gun, at least four themes emerge from this thought exercise. First, it is important to understand historical predator baselines. Second, it is important to acknowledge lifting baselines, that is, instances where previously depleted populations are recovering. Third, it is important to remember that there are many instances when stakeholder observations were initially misaligned with traditional scientific observations but were ultimately recognized as pivotal for filling data gaps. Finally, and perhaps most important, is the acknowledgement that perceived conflict is as potent as real conflict. Arguably, it may not matter if depredation has increased or decreased; the overwhelming perception from stakeholders is an increase in depredation, and this is the perceived (or real) conflict that must be addressed. [ABSTRACT FROM AUTHOR]

Objective: The Blackchin Guitarfish Glaucostegus cemiculus is endemic to the Mediterranean Sea and is critically endangered, but relevant routine laboratory data are unavailable. Our objectives were to determine the packed cell volume (PCV), comprehensive serum chemistry analytes, and serum total thyroxine (sTT4) concentration; compare serum albumin and serum globulin concentrations as measured by two different methods; and describe the blood cell morphology of healthy, free‐ranging Blackchin Guitarfish. Methods: Wild Blackchin Guitarfish were captured using a seine net. Blood samples for serum chemistry and hematological analyses were obtained and measured using routine laboratory methods. The fish were tagged and released. Result: This study included 43 Blackchin Guitarfish (17 males and 26 females) that were younger than 6 months as estimated based on total length and body weight. The median PCV (n = 23) was 22% (minimum–maximum [min–max] = 15–25%). Median sTT4 (n = 10) measured by chemiluminescence immunoassay was 7.86 nmol/L (min–max = 7.52–9.57 nmol/L). The study included a comprehensive, 25‐analyte serum chemistry analysis (e.g., serum iron and unbound and total iron‐binding capacity) and a morphological description of all blood cells. Serum electrophoresis (SEP; n = 13) yielded a consistent serum albumin‐migrating protein fraction and four globulin fractions. Serum electrophoretograms corroborating these results are presented. Conclusion: In Blackchin Guitarfish, the serum albumin‐migrating fraction measured by SEP combined with serum total protein concentration yields a much higher albumin concentration compared to that measured by bromocresol green spectrophotometry. The true identity of this albumin‐migrating fraction remains to be identified. The analytes' calculated 2.5–97.5% interpercentile intervals should be considered as reference intervals applying to Blackchin Guitarfish of similar age but should be applied cautiously to adult fish. Impact statementThis study incudes novel comprehensive basic laboratory data describing young, healthy Blackchin Guitarfish, a critically endangered species in the Mediterranean Sea. The findings significantly increase the scientific knowledge of this species, potentially contributing to its conservation. [ABSTRACT FROM AUTHOR]

Purse‐seine tropical tuna fishing in the eastern tropical Pacific Ocean (EPO) results in the bycatch of several sensitive species groups, including elasmobranchs. Effective ecosystem management balances conservation and resource use and requires considering trade‐offs and synergies. Seasonal and adaptive spatial measures can reduce fisheries impacts on nontarget species while maintaining or increasing target catches. Identifying persistently high‐risk areas in the open ocean, where dynamic environmental conditions drive changes in species' distributions, is essential for exploring the impact of fisheries closures. We used fisheries observer data collected from 1995 to 2021 to explore the spatiotemporal persistence of areas of high bycatch risk for 2 species of oceanic sharks, silky shark (Carcharhinus falciformis) and oceanic whitetip shark (Carcharhinus longimanus), and of low tuna catch rates. We analyzed data collected by fisheries scientific observers onboard approximately 200 large purse‐seine vessels operating in the EPO under 10 different flags. Fishing effort, catch, and bycatch data were aggregated spatially and temporally at 1° × 1° cells and monthly, respectively. When areas of high fishing inefficiency were closed the entire study period and effort was reallocated proportionally to reflect historical effort patterns, yearly tuna catch appeared to increase by 1–11%, whereas bycatch of silky and oceanic whitetip sharks decreased by 10–19% and 9%, respectively. Prior to fishing effort redistribution, bycatch reductions accrued to 21–41% and 14% for silky and oceanic whitetip sharks, respectively. Our results are consistent with previous findings and demonstrate the high potential for reducing elasmobranch bycatch in the EPO without compromising catch rates of target tuna species. They also highlight the need to consider new dynamic and adaptive management measures to more efficiently fulfill conservation and sustainability objectives for exploited resources in the EPO. [ABSTRACT FROM AUTHOR]

Climate change is an environmental emergency threatening species and ecosystems globally. Oceans have absorbed about 90% of anthropogenic heat and 20%–30% of the carbon emissions, resulting in ocean warming, acidification, deoxygenation, changes in ocean stratification and nutrient availability, and more severe extreme events. Given predictions of further changes, there is a critical need to understand how marine species will be affected. Here, we used an integrated risk assessment framework to evaluate the vulnerability of 132 chondrichthyans in the Eastern Tropical Pacific (ETP) to the impacts of climate change. Taking a precautionary view, we found that almost a quarter (23%) of the ETP chondrichthyan species evaluated were highly vulnerable to climate change, and much of the rest (76%) were moderately vulnerable. Most of the highly vulnerable species are batoids (77%), and a large proportion (90%) are coastal or pelagic species that use coastal habitats as nurseries. Six species of batoids were highly vulnerable in all three components of the assessment (exposure, sensitivity and adaptive capacity). This assessment indicates that coastal species, particularly those relying on inshore nursery areas are the most vulnerable to climate change. Ocean warming, in combination with acidification and potential deoxygenation, will likely have widespread effects on ETP chondrichthyan species, but coastal species may also contend with changes in freshwater inputs, salinity, and sea level rise. This climate‐related vulnerability is compounded by other anthropogenic factors, such as overfishing and habitat degradation already occurring in the region. Mitigating the impacts of climate change on ETP chondrichthyans involves a range of approaches that include addressing habitat degradation, sustainability of exploitation, and species‐specific actions may be required for species at higher risk. The assessment also highlighted the need to further understand climate change's impacts on key ETP habitats and processes and identified knowledge gaps on ETP chondrichthyan species. [ABSTRACT FROM AUTHOR]

Glucose has important roles in the development of zebrafish, the vertebrate animal model; however, in most oviparous animals, the amount of maternally provided glucose in the yolk is scarce. For these reasons, developing animals need some ways to supplement glucose. Recently, it was found that developing zebrafish, a teleost fish, undergo gluconeogenesis in the yolk syncytial layer (YSL), an extraembryonic tissue that surrounds the yolk. However, teleost YSL is evolutionarily unique, and it is not clear how other vertebrates supplement glucose. In this study, we used cloudy catshark (or Torazame catshark), an elasmobranch species which possesses a YSL‐like tissue during development, and sought for possible gluconeogenic activities in this tissue. In their yolk sac, glucose increased, and our isotope tracking analysis detected gluconeogenic activities with glycerol most preferred substrate. In addition, many of gluconeogenic genes were expressed at the YSL‐like tissue, suggesting that cloudy catshark engages in gluconeogenesis in this tissue. The gluconeogenesis in teleost YSL and a similar tissue in elasmobranch species implies conserved mechanisms of yolk metabolism between these two lineages. Future studies on other vertebrate taxa will be helpful to understand the evolutionary changes in the modes of yolk metabolism that vertebrates have experienced. [ABSTRACT FROM AUTHOR]

Small‐scale fisheries ensure food security and employment in Angolan coastal communities. These dynamic, widespread fisheries remain mostly unregulated, with limited data available despite their likely significant impact on marine megafauna. We used an interview‐based survey to investigate local fisher interactions with elasmobranchs (sharks and rays) and gather information on utilization, trade and perceptions. All fishers (n = 83) landed elasmobranchs. Most fishers considered sharks as bycatch (74.7%, n = 62), while 100% targeted rays (Order Myliobatiformes), and 62.8% (n = 52) targeted guitarfishes (Order Rhinopristiformes). Over 80% of fishers reported declining catches and sizes of elasmobranchs over the last 30 years, raising concerns about the sustainability of these fisheries. Utilization and trade routes varied depending on elasmobranch products, with exports to China (fins) and local market sales (meat). Specifically, 8.4% (n = 5) of fishers confirmed meat and fin exports to China (4.8%, n = 3). The protection of sharks was considered by 32.5% (n = 30) of respondents, while 21.7% (n = 18) believed only certain shark species should be protected. Most respondents reported that rays (80.5%, n = 67) and guitarfishes (61%, n = 51) should not be protected. Regarding the ban on fishing, none considered it for ray species, with only 6.1% (n = 5) supporting this idea for guitarfishes. We highlight the lack of elasmobranch‐specific conservation measures and the need for a multi‐pronged approach to inform policy. Considering the scale of these fisheries, management actions need to be urgently developed and implemented to ensure the sustainability of elasmobranch fisheries while securing the livelihoods of coastal communities. [ABSTRACT FROM AUTHOR]

Sertoli cells of sharks are non‐permanent components of the spermatocyst that they share exclusively with only one germ cell stage. After spermiation, all Sertoli cells, and thus the whole spent cyst, are disposed of in an area adjacent to the spermatozoal spermatocysts, that is, the resorption zone (RZ). Differences in the histology and magnitude of the RZ of the mature blue shark and Greenland shark correlate with differences in how spent cysts are dismantled. In the blue shark's RZ, the spent cyst's Sertoli nuclei were synchronously and stepwise fragmented into pyknotic bodies that were eventually resorbed in a whorl in the RZ interstitium. Conversely, cyst dismantling in the Greenland shark, that also lacked a spatially definitive RZ, revealed redundancy. One mode entailed the sloughing of the bulky Sertoli nuclei through an indistinct cyst–ductule transition area into its attached collecting ductule. A second mode entailed the asynchronous, progressive fragmentation of the bulky Sertoli nuclei into membrane‐enclosed pyknotic bodies. Both these modes solely entailed an internally coordinated demise of the spent cyst and whose basal lamina remained intact almost right to the end. Whatever the underlying mechanisms of these differences, these findings nonetheless reveal species‐specificity in the clearing up of the elasmobranch testicular parenchyma after the completion of a round of spermiogenesis. One consideration is the blue shark's expansive immune cell augmented RZ, that adjoins the animal's bone marrow equivalent tissue. The notable finding of a second conspicuous Sertoli cell type in the Greenland shark's spent cysts is also discussed. [ABSTRACT FROM AUTHOR]

The sharpnose sevengill shark (Heptranchias perlo) is a rare and poorly understood deep‐sea species, with only a few records in the Adriatic Sea over the last two centuries and a significant gap in sightings.Throughout 2023, three new records are documented in the southernmost Adriatic Sea, found at depths ranging from 391 to 452 m off Vlorë.This study marks the first comprehensive health examination of a deep‐sea shark, investigating potential trauma and injuries resulting from trawling. It encompasses pathological and histopathological examinations, supplemented by magnetic resonance imaging (MRI).The research highlights alarming post‐capture mortality rates in this data deficient species, discusses further conservation implications, and proposes protective measures for the species.Beyond addressing critical knowledge gaps, this study advocates for collaborative efforts with local fishermen to establish long‐term monitoring and obtain data on the frequency and abundance of elusive species. [ABSTRACT FROM AUTHOR]

Obtaining robust estimates of population abundance is a central challenge hindering the conservation and management of many threatened and exploited species. Close‐kin mark‐recapture (CKMR) is a genetics‐based approach that has strong potential to improve the monitoring of data‐limited species by enabling estimates of abundance, survival, and other parameters for populations that are challenging to assess. However, CKMR models have received limited sensitivity testing under realistic population dynamics and sampling scenarios, impeding the application of the method in population monitoring programs and stock assessments. Here, we use individual‐based simulation to examine how unmodeled population dynamics and aging uncertainty affect the accuracy and precision of CKMR parameter estimates under different sampling strategies. We then present adapted models that correct the biases that arise from model misspecification. Our results demonstrate that a simple base‐case CKMR model produces robust estimates of population abundance with stable populations that breed annually; however, if a population trend or non‐annual breeding dynamics are present, or if year‐specific estimates of abundance are desired, a more complex CKMR model must be constructed. In addition, we show that CKMR can generate reliable abundance estimates for adults from a variety of sampling strategies, including juvenile‐focused sampling where adults are never directly observed (and aging error is minimal). Finally, we apply a CKMR model that has been adapted for population growth and intermittent breeding to two decades of genetic data from juvenile lemon sharks (Negaprion brevirostris) in Bimini, Bahamas, to demonstrate how application of CKMR to samples drawn solely from juveniles can contribute to monitoring efforts for highly mobile populations. Overall, this study expands our understanding of the biological factors and sampling decisions that cause bias in CKMR models, identifies key areas for future inquiry, and provides recommendations that can aid biologists in planning and implementing an effective CKMR study, particularly for long‐lived data‐limited species. [ABSTRACT FROM AUTHOR]

Dextrocardia is a rare congenital malformation in humans in which most of the heart mass is positioned in the right hemithorax rather than on the left. The heart itself may be normal and dextrocardia is sometimes diagnosed during non‐related explorations. A few reports have documented atypical positions of the cardiac chambers in farmed teleost fish. Here, we report the casual finding of a left–right mirrored heart in an 85 cm long wild‐caught spiny dogfish (Squalus acanthias) with several organ malformations. Macroscopic observations showed an outflow tract originating from the left side of the ventricular mass, rather than from the right. Internal inspection revealed the expected structures and a looped cavity. The inner curvature of the loop comprised a large trabeculation, the bulboventricular fold, as expected. The junction between the sinus venosus and the atrium appeared normal, only mirrored. MRI data acquired at 0.7 mm isotropic resolution and subsequent 3D‐modeling revealed the atrioventricular canal was to the right of the bulboventricular fold, rather than on the left. Spurred by the finding of dextrocardia in the shark, we revisit our previously published material on farmed Adriatic sturgeon (Acipenser naccarii), a non‐teleost bony fish. We found several alevins with inverted (left‐loop) hearts, amounting to an approximate incidence of 1%–2%. Additionally, an adult sturgeon measuring 90 cm in length showed abnormal topology of the cardiac chambers, but normal position of the abdominal organs. In conclusion, left–right mirrored hearts, a setting that resembles human dextrocardia, can occur in both farmed and wild non‐teleost fish. [ABSTRACT FROM AUTHOR]

International trade in croaker swim bladders or maws and incidental catches in fisheries targeting croakers for their maws pose a global problem that needs addressing to protect target croakers and globally threatened small cetaceans, sharks, rays and marine turtles.The lesson of the likely imminent extinction of the vaquita porpoise (Phocoena sinus) in the Gulf of California, Mexico, owing to entanglement in gillnets targeting the totoaba croaker for its maw, is that the underlying threats to marine species must be addressed well before precipitous declines make their extinction inevitable.Opportunistic interviews with fishers and fish traders in Bangladesh indicate that the increasing demand for fish maws, selling for as much as 5,000 USD per kg, may be intensifying small‐scale coastal fisheries and bycatches of globally threatened marine wildlife, especially due to the potential for a windfall profit.In 137 croaker catches made in gillnets, sharks were bycaught in 22%, marine turtles in 8% and rays in 3% of catches. Of particular concern were six bycatches of 125 Critically Endangered scalloped hammerhead sharks (Sphyrna lewini), 11 bycatches of 20 Vulnerable (VU) olive ridley turtles (Lepidochelys olivacea) and two bycatches of 13 VU longtail butterfly rays (Gymnura poecilura).A recent IUCN Motion for 'Controlling and monitoring trade in croaker swim bladders to protect target croakers and reduce incidental catches of threatened marine megafauna' recommends conducting an analysis on the impacts of the demand for and trade in fish maws on croaker species and threatened marine megafauna, regulating trade in fish maws through national laws and developing a potential proposal to list croaker species in the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).To prevent species extinctions, additional measures focusing on fishery management will be needed. [ABSTRACT FROM AUTHOR]

There is intense public interest surrounding the conservation and management of sharks, including a debate over whether sustainable shark fisheries are possible or fishing bans on sharks are needed to conserve these animals. An important but rarely discussed data point in discussions of global shark fisheries is the case of British Columbia's fishery for Pacific spiny dogfish, Squalus suckleyi, which in 2011 became the first Marine Stewardship Council−certified shark fishery anywhere in the world. A few years later, despite reportedly healthy local stocks and thriving global markets for this shark, the fishery voluntarily withdrew its MSC certification, and in recent years more than 95% of the quota for Pacific spiny dogfish has been left in the water. This study provides insight into what happened to this fishery through a review of grey literature and a series of stakeholder interviews with British Columbian fishermen, fish processors, managers and environmentalists. It is a rare case study of a fishery that largely ceased operations without a clear mechanistic explanation like a stock collapse, a government mandate to limit fishing or a clear shift in market demand. This fishery appears to have been affected by the combination of several factors, including a temporary reduction in biomass due to oceanographic effects, potential blowback from overly broad environmental messaging that did not distinguish between sustainable and unsustainable shark fisheries, management changes resulting in altered fishing incentives and changes to processing capacity associated with consolidating the fishing industry into ownership by relatively few large companies. [ABSTRACT FROM AUTHOR]

Isolated cases of skin pigment disorders, including leucism, in sharks and rays have been reported for multiple species. Nonetheless, the morphological basis behind these chromatic anomalies has not been examined histologically. In this study, the authors quantified and compared the presence of melanin in multiple tissue samples of leucistic and fully pigmented blacktip sharks Carcharhinus limbatus. The authors' results support lack of melanin to be responsible for leucistic colouration. The histological differences responsible were evaluated. [ABSTRACT FROM AUTHOR]

Post‐release mortality threatens shark populations already imperiled by overfishing, capture stress, and a changing climate. Few studies have quantified post‐release mortality for sharks captured in land‐based recreational fisheries. From 2018 to 2021, a land‐based shark post‐release mortality study was conducted and identified water temperature and species‐specific behavior as contributing factors to post‐release mortality. The purpose of this study was to estimate the effectiveness of disseminating the recommendation for best practices to recreational shark anglers and to determine if this information influenced angler behavior. Awareness of our post‐release mortality study influenced an angler's likely release behavior, with an increase in sharks landed in the water and corresponding decrease of sharks landed on dry sand. This study demonstrated direct evidence of conservation‐based changes in angler behavior following effective research communication and involvement of anglers in research. Outreach and engagement initiatives aimed at providing best handling practices to recreational anglers should be easily digestible, widely available, and an important component of future research. [ABSTRACT FROM AUTHOR]

We report the first case of partial albinism in the Critically Endangered angelshark, Squatina squatina. The encounter with this specimen took place while SCUBA diving on the beach of Tufia, located on the east coast of the island of Gran Canaria on 2 April 2021. This is also the first confirmed finding of an albino elasmobranch specimen in the Canary Island archipelago. [ABSTRACT FROM AUTHOR]

Aim: Large marine predators, such as cetaceans and sharks, play a crucial role in maintaining biodiversity patterns and ecosystem function, yet few estimates of their spatial distribution exist. We aimed to determine the species richness of large marine predators and investigate their fine‐scale spatiotemporal distribution patterns to inform conservation management. Location: The Hauraki Gulf/Tīkapa Moana/Te Moananui‐ā‐Toi, Aotearoa/New Zealand. Methods: We conducted a replicate systematic aerial survey over 12 months. Flexible machine learning models were used to explore relationships between large marine predator occurrence (Bryde's whales, common and bottlenose dolphins, bronze whaler, pelagic and immature hammerhead sharks) and environmental and biotic variables, and predict their monthly distribution and associated spatially explicit uncertainty. Results: We revealed that temporally dynamic variables, such as prey distribution and sea surface temperature, were important for predicting the occurrence of the study species and species groups. While there was variation in temporal and spatial distribution, predicted richness peaked in summer and was the highest in coastal habitats during that time, providing insight into changes in distributions over time and between species. Main Conclusions: Temporal changes in distribution are not routinely accounted for in species distribution studies. Our approach highlights the value of multispecies surveys and the importance of considering temporally variable abiotic and biotic drivers for understanding biodiversity patterns when informing ecosystem‐scale conservation planning and dynamic ocean management. [ABSTRACT FROM AUTHOR]

Sharks, rays, and chimaera form the clade Chondrichthyes, an ancient group of morphologically and ecologically diverse vertebrates that has played an important role in our understanding of gnathostome evolution. Increasingly, studies seek to investigate evolutionary processes operating within the chondrichthyan crown group, with the broad aim of understanding the driving forces behind the vast phenotypic diversity observed among its constituent taxa. Genetic, morphological, and behavioral studies have all contributed to our understanding of phenotypic evolution yet are typically considered in isolation in the context of Chondrichthyes. In this viewpoint, I discuss why such isolation is prevalent in the literature, how it constrains our understanding of evolution, and how it might be overcome. I argue that integrating these core fields of organismal biology is vital if we are to understand the evolutionary processes operating in contemporary chondrichthyan taxa and how such processes have contributed to past phenotypic evolution. Despite this, the necessary tools to overcome this major limitation already exist and have been applied to other taxa. [ABSTRACT FROM AUTHOR]

The occurrence of smooth muscle sphincters around gastric gland tubules in the cardiac stomach of some elasmobranch species is reported for the first time. These "microsphincters" took the form of a twisted torus, approximately 12–16 muscle fibres thick, that could fully constrict the gland tubules. However, their inconsistent positioning does not suggest a role in partitioning the tubules from the stomach lumen or in modulating secretory activity. Further research is required to ascertain the full taxonomic occurrence of these structures across the Elasmobranchii and to elucidate their function. [ABSTRACT FROM AUTHOR]

Laboratory‐based studies examining fish physiological and behavioural responses to temperature can provide important insight into species‐specific habitat preferences and utilisation, and are especially useful in examining vulnerable life stages that are difficult to study in the wild. This study couples shuttle box behavioural experiments with respirometry trials to determine the temperature preferences and metabolic thermal sensitivity of juvenile California horn shark (Heterodontus francisci) and leopard shark (Triakis semifasciata). As juveniles, these two species often occupy similar estuarine habitats but display contrasting behaviours and activity levels – H. francisci are relatively sedentary, whereas T. semifasciata are more active and mobile. This study shows that juvenile H. francisci and T. semifasciata have comparable thermal preferences and occupy similar temperature ranges, but H. francisci metabolism is more sensitive to acute changes in temperature as expressed through a higher Q10 (H. francisci = 2.58; T. semifasciata = 1.97; temperature range: 12–24°C). Underlying chronic temperature acclimation to both warm (21°C) and cool (15°C) representative seasonal temperatures did not appear to significantly affect these parameters. These results are discussed in the context of field studies examining known distributions, habitat and movement patterns of H. francisci and T. semifasciata to better understand the role of temperature in species‐specific behaviour. Juvenile H. francisci likely target thermally stable environments, such as estuaries that are close to their preferred temperature, whereas juvenile T. semifasciata metabolism and behaviour appear less dependent on temperature. [ABSTRACT FROM AUTHOR]

In the context of marine species declines in data‐limited regions, local ecological knowledge (LEK) is a valuable source of information on species ecology and historical trends. LEK can also help understand how threatened species exist within a local culture, in terms of their uses and values, and reveal attitudes towards their conservation. Rhino rays (guitarfish and wedgefish) are highly threatened by overfishing with most species critically endangered, yet poorly studied in countries like India that fish them the most.We drew on LEK to understand the socio‐ecological status of rhino rays in Goa, on the west coast of India. We investigated their habitat use and seasonality, interaction with fisheries, socio‐economic uses and relational values. We also explored attitudes of fishers towards rhino rays and their conservation. A combination of semistructured interviews and key informant interviews (88 in total) was conducted with fishers at multiple sites.Local knowledge suggests that nearshore habitats around river mouths form important nursery grounds for some rhino rays, and provided insights on their seasonality and breeding. Rhino rays appeared to be targeted historically but are entirely bycaught at present, with highest catches in gillnets and in the South Goa district, during September and October. LEK indicated that taxa like sawfish (Pristis spp.) and wedgefish (Rhynchobatus spp.) have severely declined or disappeared from this region. We coded different relational values, from recreation (rhino rays are consumed and enjoyed with alcohol) to symbolic values (rhino rays are considered lucky). All key informants expressed positive attitudes towards rhino ray conservation and stated that a ban on landing these species would have little to no impact on fisher earnings.The usefulness of LEK suggests it should be brought into the scientific mainstream to support development of more equitable and socially appropriate management plans. Fostering relational values can reinforce fishers' positive attitudes, thereby enhancing rhino ray conservation. Their low commercial value and potentially high post‐capture survival suggest that using norm‐based approaches to promote live release may be successful. Further research on rhino ray ecology and human dimensions can support the development of appropriate conservation interventions. Read the free Plain Language Summary for this article on the Journal blog. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Flake and shark samples were purchased from outlets in several coastal Australian regions and genetically barcoded using the cytochrome oxidase subunit 1 (CO1) gene to investigate labelling reliability and species‐specific sources of ambiguously labelled fillets. Of the 41 shark fillet samples obtained, 23 yielded high‐quality CO1 sequences, out of which 57% (n = 13) were labelled ambiguously (misleading) and 35% (n = 8) incorrectly. In contrast, barramundi fillets, which are widely available and sought after in Australian markets, were shown to be accurately labelled. Species identified from shark samples, including the shortfin mako (n = 3) and the scalloped hammerhead (n = 1), are assessed by the IUCN as endangered and critically endangered, respectively, with several others classified as vulnerable and near threatened. [ABSTRACT FROM AUTHOR]

Online research methods are increasingly used in conservation science to monitor and collect data on online wildlife trade. Shark‐like rays (Rhinopristiformes) are among the most threatened vertebrates, prized for their high‐value fins while other uses for their derivatives are largely unrecognized in the literature. The bowmouth guitarfish (Rhina ancylostomus) is characterized by ridges of enlarged thorns, sometimes sold as amulets. Listed on the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) Appendix II, the thorn‐market has been ignored and undocumented. Using systematic, retrospective online searches, we recorded 977 bowmouth‐derivatives for sale. In our global and multi‐lingual scope, 97% of products were offered from Thailand, despite prohibited trade. 98% of all products were thorns (USD3‐300) and sold alongside high‐profile CITES‐listed taxa (e.g., tiger claws). Consistent advertisements from 2012 revealed a previously unquantified trade of an often‐neglected marketplace in elasmobranch research. Our findings offer insight into the drivers of the thorn trade, potentially rooted in cultural beliefs. Our accessible research methods can be applied internationally and across species, providing quantitative and qualitative insights on aspects of the wildlife trade of a critically endangered fish. Continued monitoring of online markets, like this study, is necessary to fill critical gaps for informed policy and species‐specific management. [ABSTRACT FROM AUTHOR]

Elasmobranchs (sharks and rays) are charismatic cartilaginous fish, popular in public aquaria. Almost 200 shark and ray species are listed as threatened by the International Union for Conservation of Nature (IUCN), demonstrating the importance of captive breeding and research programmes. Limited studies investigate diseases of elasmobranchs in captive and free‐living environments, and among available literature neoplasia is rarely reported, with even fewer cases of lymphoid neoplasia documented. This article outlines the first reports of lymphoid neoplasia in three elasmobranch species in which haematopoietic neoplasms have not been reported to date. It summarizes signalment, history and histopathologic findings in an undulate ray, Raja undulata (Lacepede), a common smooth‐hound, Mustelus mustelus (Linnaeus) and a bat ray, Myliobatis californica (Gill). Lesions were confirmed in a wide range of tissues and evidence of lymphoid leukaemia was seen in two cases. This small‐scale review demonstrates that lymphoid neoplasia should be considered as a differential diagnosis in elasmobranchs presenting with lethargy and anorexia and highlights the challenges of immunohistochemical work up. [ABSTRACT FROM AUTHOR]

With the increasingly imperilled status of shark populations, there is a pressing need to evaluate management solutions. Given the threats posed by fishing, marine reserves (MRs) present a promising option.Ata Whenua (Fiordland) in the South Island of Aotearoa/New Zealand is an ideal location to investigate this phenomenon owing to the presence of several shark species in coastal MRs.One‐hundred and sixty‐seven baited remote underwater video deployments were made in five MRs. A multi‐model inference approach using generalized linear modelling was used to assess the combined effect of the MRs on two trophic groups of coastal sharks.Generalized linear modelling was used to assess the effect of protection on, firstly, the presence of broadnose sevengill sharks (Notorynchus cepedianus), while accounting for variations in environmental variables, and secondly, the combined relative abundance of mesopredatory sharks detected (spiny dogfish, Squalus acanthias; school shark, Galeorhinus galeus; and carpet shark, Cephaloscyllium isabellum).Mesopredators had a higher relative abundance in MRs by a factor of 2.5 and there was a strong significant effect of protection, suggesting that MRs have led to an increase in their abundance or a change in distribution. In contrast, there was no effect of protection detected for sevengill sharks.It is concluded that the relatively small (<40 km2) MRs sampled do not provide conservation benefits for a large, mobile shark, but that they are potentially large enough to offer protection for mesopredatory sharks with smaller home ranges.To be effective for shark conservation, we therefore recommend that MRs need to be appropriately sized for the ranging behaviour of the target species for protection. [ABSTRACT FROM AUTHOR]

The evolutionary context in which shark bioluminescence originated is poorly understood, despite it being critical to uncovering influential factors in the evolutionary history and diversity of living chondrichthyans as well as the mechanisms of deep‐water colonization by vertebrates. This study provides the first joint reconstruction of the habitats, lifestyles, and occurrence of bioluminescence in the evolution of squalomorph sharks using ancestral state estimation analysis to resolve the timing of deep‐sea colonization, the evolutionary origin of bioluminescence and the ancestral ecologies of this group. The results suggest that most squalomorphs originated in neritic environments from where they colonized deep waters on several independent occasions during the Late Jurassic and Early Cretaceous, predating most of the previous estimates of the timing of this event. The colonization of the deep sea took place via the benthic zone, in contrast to the view that an intermediate mesopelagic stage occurred during this ecological transition. Finally, the analyses accounting for uncertainty of the presence of bioluminescence strongly support that this trait evolved only once among sharks in a bathydemersal ancestor. This study reveals that shark bioluminescence evolved in a complex scenario that combines elements of several previous proposals, and enriches our perspective on the sequence of events that characterized the vertebrate conquest of the deep sea. [ABSTRACT FROM AUTHOR]

The use of size‐selective fishing gear has been fundamental for the successful management of shark populations. For the main Australian shark fisheries, available data sets on gillnet selectivity experiments conducted since the 1990s were used to estimate gillnet selectivity parameters for nine commonly caught non‐target species: broadnose, draughtboard, Port Jackson and school sharks, common and southern sawsharks, smooth hammerhead and spikey and whitespotted dogfish. Size at selection increased with mesh size, but it varied with species, with some species having broader selectivity curves due to their particular morphological features. In particular, smooth hammerhead had much broader selectivity curves and larger length at maximum selection than other species of comparable size such as the broadnose shark. The selectivity curves derived in this study will allow a more accurate interpretation of catch size composition and model‐based assessments of stock status of these species [ABSTRACT FROM AUTHOR]

Marine wildlife stranding is a global phenomenon, and for some taxonomic groups, these events are well monitored and documented. Although sharks are among the most threatened vertebrates, strandings have historically been neglected, with little information on this topic currently available. To address this knowledge gap, a systematic review on scientific publications from indexed databases, multimedia material and citizen science databases was performed. A total of 3150 reports were recovered, with strandings dating back to 1880 including 89 species of sharks from 22 families. Both single/small‐scale and mass stranding events were observed. Species ranged from coastal to oceanic, with reports for small‐, medium‐ and large‐sized sharks. Leopard (Triakis semifasciata, Triakidae), brown smooth‐hound (Mustelus henlei, Triakidae) and salmon sharks (Lamna ditropis, Laminidae) were the species with most records. Females stranded significantly more than males, but juveniles and adults were affected in the same proportion. Shark strandings were reported for 47 countries, and the United States was the most representative location, highlighting the states of California and Oregon. Survival rates were extremely low, indicating that stranded sharks are more vulnerable that other taxonomic groups. Potential and putative causes were identified, being similar to those suggested for marine mammal strandings. Our results indicate that although they occur to a lesser extent when compared to mammals, shark strandings are neglected, and urgent measurements are necessary to better understand, document and to properly respond to these events. [ABSTRACT FROM AUTHOR]

Multiple paternity (MP) in the brown smooth‐hound shark (Mustelus henlei) was assessed in 15 litters (15 mothers and 97 embryos) collected in the northern Gulf of California of which 86.7% were sired by more than one male (i.e., from 2 to 4 sires). When taken together with results from previous studies, this record indicates that there is regional variation in MP in M. henlei in the northeastern Pacific. This pattern is associated with variations in the reproductive traits of each population (e.g., female size and litter size). In the Gulf of California, the results of a generalized linear model (GLZ) indicated that the litters of larger females had a higher probability of MP compared to those of smaller females. [ABSTRACT FROM AUTHOR]

Ocean acidification can cause dissolution of calcium carbonate minerals in biological structures of many marine organisms, which can be exacerbated by warming. However, it is still unclear whether this also affects organisms that have body parts made of calcium phosphate minerals (e.g. shark teeth), which may also be impacted by the 'corrosive' effect of acidified seawater. Thus, we examined the effect of ocean acidification and warming on the mechanical properties of shark teeth (Port Jackson shark, Heterodontus portusjacksoni), and assessed whether their mineralogical properties can be modified in response to predicted near‐future seawater pH (–0.3 units) and temperature (+3°C) changes. We found that warming resulted in the production of more brittle teeth (higher elastic modulus and lower mechanical resilience) that were more vulnerable to physical damage. Yet, when combined with ocean acidification, the durability of teeth increased (i.e. less prone to physical damage due to the production of more elastic teeth) so that they did not differ from those raised under ambient conditions. The teeth were chiefly made of fluorapatite (Ca5(PO4)3F), with increased fluoride content under ocean acidification that was associated with increased crystallinity. The increased precipitation of this highly insoluble mineral under ocean acidification suggests that the sharks could modulate and enhance biomineralization to produce teeth which are more resistant to corrosion. This adaptive mineralogical adjustment could allow some shark species to maintain durability and functionality of their teeth, which underpins a fundamental component of predation and sustenance of the trophic dynamics of future oceans. [ABSTRACT FROM AUTHOR]

Twelve teleosts and one shark species were recorded chafing against eight different species of shark (Figs. Keywords: behavior; chafing; cleaning station; dermal denticles; ecological function; fish; microbiome; parasite; predation risk; shark; skin; symbiosis EN behavior chafing cleaning station dermal denticles ecological function fish microbiome parasite predation risk shark skin symbiosis 1 4 4 01/05/22 20220101 NES 220101 Ectosymbionts, such as bacteria and parasites, are found on the body surface of the host organisms throughout the ecosystems across the world. Future studies investigating the profilometry of sharks' dermal denticles and their efficacy in removing skin irritants with respect to the location on the body will provide further insights into the function of dermal denticle as a cleaning mechanism. [Extracted from the article]

Dwarf sperm whales (Kogia sima) have been studied rarely at sea. We used photo‐identification, boat‐ and drone‐based behavioral observations, and citizen science photo contributions to examine site fidelity, spatial use, and behavior in Hawaiʻi. Sighting rates were highest in island slope (500–1,000 m) waters. Over 40% of photo‐identified individuals were linked by association in the same social network. More than half of the very distinctive individuals were seen more than once, and 28.5% were seen in multiple years, with one individual seen 14 times over a 15‐year span. Resighted individuals and those in the main cluster of the social network were found in significantly shallower water than individuals that were not resighted or that were in isolated clusters. Distances between resighting locations suggest small home ranges. This suggests an insular slope‐dwelling population that overlaps with an offshore population. Evidence of unsuccessful predatory attempts by large sharks was recorded on four individuals, and linear wounds consistent with interactions with line fisheries were documented on three individuals. Surface and subsurface behavior recorded by drone revealed vigilance behavior likely to minimize predation risk. Lessons learned from this study can be applied elsewhere to increase knowledge of this poorly known and difficult‐to‐study species. [ABSTRACT FROM AUTHOR]

Objective: There are increasing numbers of shark attacks in Australasian waters, with death commonly resulting from uncontrolled lower limb bleeding. The present study aims to determine the most effective first aid method using immediately available resources for controlling lower limb haemorrhage, which could be provided by single unsupported rescuer. Methods: The present study was a clinical trial performed at a single tertiary referral hospital. Healthy volunteers who completed a screening questionnaire, a baseline popliteal velocity measurement and then consented were eligible. The present study used Doppler ultrasound to record the reduction in popliteal artery peak systolic velocity created by surfboard leg rope tourniquet and by inguinal region external compression in healthy volunteer subjects with and without a wetsuit. Leg circumference and sex data were also collected. Results: Pooled data from each intervention without and with a wetsuit showed that inguinal compression resulted in a mean reduction of popliteal artery peak systolic velocity of 89.7% (95% CI 83.9%, 95.5%) compared to leg rope application 43.8% (95% CI 34.5%, 53.1%; P ≤ 0.001). There was no significant influence by the wetsuit on effectiveness of either intervention technique. Conclusion: The present study has shown that manual inguinal compression, an easily taught first aid technique, can reliably completely stop or substantially reduce blood loss in the setting of a lower limb injury and is superior to an improvised tourniquet. [ABSTRACT FROM AUTHOR]

In recent years, the incorporation of lower levels of organization to the understanding of population ecology, has led to an increase in interest for animal personality and individual foraging specialization. Despite these topics investigating comparable phenomena, that is, individual consistency in behaviour and in food resource use respectively, they have rarely been investigated together.Food resource use is thought to be at the interface between personality and life history. More explorative individuals in a population, for example, are thought to increase encounter rates with food resources and consequently have faster growth than less explorative conspecifics.Such hypotheses have so far only received partial support, and the link between personality and life history is increasingly speculated to be plastic and dependent on spatio‐temporal variation in ecological conditions. Intraspecific competition and/or predation risk, for example are known to influence foraging specialization.Here, we investigated the relationship between exploration personality of juvenile lemon sharks Negaprion brevirostris (measured in captivity) and foraging habitat use (high risk vs. low risk; measured via stable isotope analysis in the field) in relation to conspecific and predator abundance.We identified predator abundance as the main driver for the association between foraging habitat and exploration personality. When predators were less abundant, increased exploration was associated with foraging in riskier habitats. When predator abundance increased, an inverse relationship occurred, with less explorative individuals using more dangerous habitat.We conclude that the relationship between personality and resource use is plastic and context dependent, which could explain the inconclusive results of previous studies investigating links between personality and life history. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Ladybird homeobox (Lbx) transcription factors have crucial functions in muscle and nervous system development in many animals. Amniotes have two Lbx genes, but only Lbx1 is expressed in spinal cord. In contrast, teleosts have three lbx genes and we show here that zebrafish lbx1a, lbx1b, and lbx2 are expressed by distinct spinal cell types, and that lbx1a is expressed in dI4, dI5, and dI6 interneurons, as in amniotes. Our data examining lbx expression in Scyliorhinus canicula and Xenopus tropicalis suggest that the spinal interneuron expression of zebrafish lbx1a is ancestral, whereas lbx1b has acquired a new expression pattern in spinal cord progenitor cells. lbx2 spinal expression was probably acquired in the ray‐finned lineage, as this gene is not expressed in the spinal cords of either amniotes or S. canicula. We also show that the spinal function of zebrafish lbx1a is conserved with mouse Lbx1. In zebrafish lbx1a mutants, there is a reduction in the number of inhibitory spinal interneurons and an increase in the number of excitatory spinal interneurons, similar to mouse Lbx1 mutants. Interestingly, the number of inhibitory spinal interneurons is also reduced in lbx1b mutants, although in this case the number of excitatory interneurons is not increased. lbx1a;lbx1b double mutants have a similar spinal interneuron phenotype to lbx1a single mutants. Taken together these data suggest that lbx1b and lbx1a may be required in succession for correct specification of dI4 and dI6 spinal interneurons, although only lbx1a is required for suppression of excitatory fates in these cells. Research Highlights: lbx1 spinal expression and function is conserved in vertebrates. In contrast, zebrafish lbx1b and lbx2 have novel spinal expression patterns that probably evolved in the ray‐finned vertebrate lineage (lbx2) or teleosts (lbx1b). [ABSTRACT FROM AUTHOR]

Historically, the Mediterranean Sea supported a rich shark fauna. Presently, however, populations of most shark species have significantly declined, largely due to intense fishing pressure.Interviews with crew members of bottom trawlers, drifting longliners and bottom longliners operating off the Costa Brava (Catalonia, NE Spain) were conducted between October 2016 and July 2017 in order to gather information on the current bycatch rate of several shark species.Interviews covered 41.2% of the fleet and respondents were asked for the bycatch of selected shark species—Alopias vulpinus, Cetorhinus maximus, Galeorhinus galeus, Hexanchus griseus, Isurus oxyrinchus, Mustelus spp., Prionace glauca, and Squalus acanthias—in two distinct time periods.Bottom trawlers captured the highest diversity of species (eight) followed by bottom longliners (seven), and drifting longliners (three). Most respondents (89.7%) declared having captured at least one shark from 2006 to 2016 but only 56.4% declared having captured at least one shark from 2016 to 2017.From 2016 to 2017, the whole fleet captured 89 specimens of H. griseus (95% confidence interval (CI) = 145, 34), 14 of G. galeus (95% CI = 30, 0), 3 of A. vulpinus (95% CI = 8, 0), 3 of I. oxyrinchus (95% CI = 8, 0), 3 of C. maximus (95% CI = 6, 0), and no Mustelus spp. The total bycatch of P. glauca and S. acanthias was uncertain due to extremely loose confidence intervals.A significant decline was perceived by fishermen in the bycatch of C. maximus and S. acanthias, whereas the bycatch of H. griseus was considered to have remained stable.This study suggests a dramatic reduction in the abundance of most of the medium‐sized and large sharks of the Costa Brava and the likely disappearance of Mustelus spp. from the area. Only H. griseus, S. acanthias, and P. glauca are still being bycaught frequently. [ABSTRACT FROM AUTHOR]

Throughout their life history, many animals transition among heterogeneous environments to facilitate behaviours such as reproduction, foraging and predator avoidance. The dynamic environmental and biological conditions experienced by mobile species are integrated in the chemical composition of their tissues, providing retrospective insight into movement.Here, we present a unique application of nitrogen stable isotope clocks ('isotopic clocks'), which integrate tissue turnover rates, consumer stable isotope ratios and habitat‐specific isotope baselines to predict time‐since‐immigration and the timing of habitat shifts in a migratory species. Nitrogen stable isotope values of blood plasma collected from juvenile sand tiger sharks Carcharias taurus, a species known to undertake seasonal movements between ocean and estuarine environments, were used to derive estimates of time‐since‐immigration and the timing of seasonal habitat shifts undertaken by this species.Nitrogen isotopic clocks estimated for 65 juvenile sand tiger sharks sampled across 6 years indicated that individual sharks predominantly arrived to estuarine habitats between June and July, with some individuals arriving as early as mid‐May. These estimates were validated by comparing isotope‐derived estuarine arrival times with those from acoustically tracked individuals. The median estuarine arrival day estimates from our isotopic approach aligned with estimates from acoustic telemetry for each sampling population.Sensitivity analyses indicated that isotopically inferred time‐since‐immigration and estuarine arrival estimates were robust to variation in isotopic turnover rate and diet tissue discrimination factors under multiple modelling scenarios. This suggests that parameterization of the nitrogen isotopic clock provides reliable estimates of time‐since‐immigration and day of arrival into new habitats if isotopic variation exists between origin and new locations.Our study presents a unique application of telemetry‐validated isotope clocks to derive retrospective estimates of time‐since‐immigration and timing of habitat shifts for animals that seasonally traverse heterogeneous environments. This approach can be readily applied across many temporal and spatial scales, and to other species and ecosystems, to facilitate rapid assessment of changes in animal habitat use and broader ecosystem structure. [ABSTRACT FROM AUTHOR]

While the negative effects of consumptive pressures on marine predators are well established, the effects of increasing non‐consumptive activities such as wildlife tourism are still understudied. As such, the long‐term effects of the provision of bait on shark behaviour are still unclear. Here, we assessed the effects of provisioning using a Control‐Impact design on the spatial use and level of residency of the blacktip reef shark Carcharhinus melanopterus over a 2‐year period. We used effect sizes to model the relative changes in residency between provisioning and non‐provisioning sites. Sharks showed a high degree of residency and significant changes in their habitat use which persisted overnight while the activity ceased. We suggest that provisioning activities can affect species with high level of residency such as the blacktip reef shark. Further research is needed to better understand how these behavioural modifications can alter the fitness of this species. It is important to adapt shark provisioning activities to limit the induced changes in habitat use. [ABSTRACT FROM AUTHOR]

Keywords: animal-borne video; behavior; morphology; predator-prey interaction; sea turtle; shark; trait compensation EN animal-borne video behavior morphology predator-prey interaction sea turtle shark trait compensation 1 4 4 04/03/21 20210401 NES 210401 Predation is a primary selection pressure contributing to both the morphological and behavioral adaptations of organisms (Brodie 1983, Lima and Dill 1990). Animal-borne video from a sea turtle reveals novel anti-predator behaviors 1 for full interaction. gl Although our single observation should not be considered to redefine sea turtle anti-predator behavior, it raises a new hypothesis regarding sea turtle anti-predator behaviors and the evolutionary forces that shape them. However, studying the anti-predator behaviors of aquatic taxa such as sea turtles is currently limited by the difficulty of observing the natural behaviors of free-ranging individuals at sea (Heithaus et al. 2008). [Extracted from the article]

The idea that the presence of sharks impacts the behavior of mesopredatory reef fishes is controversial and lacks clear evidence at reef‐wide scales. We compared the abundance and behavior of these reef fishes in response to the presence of reef sharks using Baited Remote Underwater Video System (BRUVS) deployments in two adjacent reef systems where sharks have either been exclusively targeted by fishing or protected by a no‐take marine reserve. For a subset of videos, we also compared the behavior of mesopredatory reef fishes immediately before and after the appearance of sharks in the video. On reefs where sharks were more abundant, mesopredatory fishes spent less time swimming in midwater (i.e., away from shelter) and guarding bait compared to reefs where sharks have been selectively removed. The same responses occurred after the appearance of sharks in the video. Reactions to sharks varied both in strength and type among species of mesopredator and were mediated by the availability of shelter on the reef and, for one species, by the levels of activity of the reef sharks. In contrast, we did not find that the presence of sharks influenced the abundance of mesopredators at either reef system across hour‐long videos or immediately before and after a shark appeared in the video. Collectively, our findings show that the presence of sharks reduces the propensity of mesopredatory fish to engage in potentially risk‐prone behaviors over large spatial scales and that these interactions are mediated by the behavioral characteristics of both predators and prey, and the environment in which they co‐occur. Our results are consistent with the idea that sharks as predators or larger competitors initiate changes in the behavior of mesopredatory reef fishes likely to affect trophic structuring within coral reef ecosystems. [ABSTRACT FROM AUTHOR]

A mega‐tooth belonging to a Miocene fossil shark was discovered along the shores of the Arabian Sea inside one of the Neolithic domestic settlements at Sharbithat (SHA‐10) (Sultanate of Oman). Attributed to a representative of the extinct genus Otodus (Megaselachus), this tooth is the first ever discovered in the Arabian Peninsula. In the field, research permitted the localization and study, a few kilometres away, of the palaeontological deposit where this retrieval was made. The shark, traditionally extensively hunted on the shores of the Arabian Sea, is well attested in the region's Neolithic ichthyological assemblages. Moreover, during this period, some groups of seaborne hunters were specialized in this form of fishing, which was indeed quite dangerous. But why did an individual some 5,500 years ago collect this curio, an unusual fossil, but also one he could easily recognize? The fossils of large sharks sometimes played an important part in ancient societies. Could this also have been the case in South‐Eastern Arabia? [ABSTRACT FROM AUTHOR]

Five prosomatostatin genes (PSST1, PSST2, PSST3, PSST5, and PSST6) have been recently identified in elasmobranchs (Tostivint et al., General and Comparative Endocrinology, 2019, 279, 139–147). In order to gain insight into the contribution of each somatostatin to specific nervous systems circuits and behaviors in this important jawed vertebrate group, we studied the distribution of neurons expressing PSST mRNAs in the central nervous system (CNS) of Scyliorhinus canicula using in situ hybridization. Additionally, we combined in situ hybridization with tyrosine hydroxylase (TH) immunochemistry for better characterization of PSST1 and PSST6 expressing populations. We observed differential expression of PSST1 and PSST6, which are the most widely expressed PSST transcripts, in cell populations of many CNS regions, including the pallium, subpallium, hypothalamus, diencephalon, optic tectum, midbrain tegmentum, and rhombencephalon. Interestingly, numerous small pallial neurons express PSST1 and PSST6, although in different populations judging from the colocalization of TH immunoreactivity and PSST6 expression but not with PSST1. We observed expression of PSST1 in cerebrospinal fluid‐contacting (CSF‐c) neurons of the hypothalamic paraventricular organ and the central canal of the spinal cord. Unlike PSST1 and PSST6, PSST2, and PSST3 are only expressed in cells of the hypothalamus and in some hindbrain lateral reticular neurons, and PSST5 in cells of the region of the entopeduncular nucleus. Comparative data of brain expression of PSST genes indicate that the somatostatinergic system of sharks is the most complex reported in any fish. [ABSTRACT FROM AUTHOR]

In addition to canonical TCR and BCR, cartilaginous fish assemble noncanonical TCR that employ various B‐cell components. For example, shark T cells associate alpha (TCR‐α) or delta (TCR‐δ) constant (C) regions with Ig heavy chain (H) variable (V) segments or TCR‐associated Ig‐like V (TAILV) segments to form chimeric IgV‐TCR, and combine TCRδC with both Ig‐like and TCR‐like V segments to form the doubly rearranging NAR‐TCR. Activation‐induced (cytidine) deaminase‐catalyzed somatic hypermutation (SHM), typically used for B‐cell affinity maturation, also is used by TCR‐α during selection in the shark thymus presumably to salvage failing receptors. Here, we found that the use of SHM by nurse shark TCR varies depending on the particular V segment or C region used. First, SHM significantly alters alpha/delta V (TCRαδV) segments using TCR αC but not δC. Second, mutation to IgHV segments associated with TCR δC was reduced compared to mutation to TCR αδV associated with TCR αC. Mutation was present but limited in V segments of all other TCR chains including NAR‐TCR. Unexpectedly, we found preferential rearrangement of the noncanonical IgHV‐TCRδC over canonical TCR αδV‐TCRδC receptors. The differential use of SHM may reveal how activation‐induced (cytidine) deaminase targets V regions. [ABSTRACT FROM AUTHOR]

The study of the fish bones from the Neolithic shell midden of Suwayh 1, excavated in the 2000s, identified a total of 1060 identifiable fish bones, from 23 families, 33 genera and 28 different species. Radiocarbon dating demonstrates that the sites date to the early 6th to mid 5th millennium BC. The results follow an eight‐phase chronology highlighted by an earlier malacological study. The most important taxa were the Carcharhinidae (requiem shark), Rhinopteridae (cownose rays), Sparoidea (Sparidae and Lethrinidae: sea breams and emperors) and Ariidae (sea catfishes). The results of the fish study show that the Suwayh lagoon must have gradually opened up to the sea and been populated with mangroves. The unique presence of so many sharks at this site seems to indicate that the inhabitants had a special interest in shark fishing and that their location was ideal for this specialised activity. Two types of fishing nets and hooks have been discovered, which require the use of different fishing techniques. [ABSTRACT FROM AUTHOR]

This study developed a portable, low‐cost field respirometer for measuring oxygen consumption rates of large‐bodied fishes. The respirometer performed well in laboratory tests and was used to measure the oxygen consumption rates (M˙O2) of bull sharks Carcharhinus leucas (mean: 249.21 ± 58.10 mg O2 kg−1 h−1 at 27.05°C). Interspecific comparisons and assessments of oxygen degradation curves indicated that the respirometer provided reliable measurements of M˙O2. This system presents a field‐based alternative to laboratory respirometers, opening opportunities for studies on species in remote localities, increasing the ability to validate physiological field studies. [ABSTRACT FROM AUTHOR]

In this study, life‐history traits (maximum and average size, size at maturity and fecundity) of two congeneric smooth‐hounds, Mustelus mustelus and Mustelus punctulatus, which share a geographical distribution and experience a similar fishing exploitation, were estimated and compared between species. The results indicated a lower maximum and average size, a lower size at maturity and a higher fecundity in M. punctulatus compared with those in M. mustelus. Considering that these two species co‐occur in the same areas and are caught by the same fishing gears, the results indicate a higher vulnerability to exploitation of M. mustelus compared with that of M. punctulatus. [ABSTRACT FROM AUTHOR]

It is challenging to assess long‐term trends in mobile, long‐lived and relatively rare species such as sharks. Despite ongoing declines in many coastal shark populations, conventional surveys might be too fleeting and too recent to describe population trends over decades to millennia. Placing recent shark declines into historical context should improve management efforts as well as our understanding of past ecosystem dynamics.A new palaeoecological approach for surveying shark abundance on coral reefs is to quantify dermal denticle assemblages preserved in sediments. This approach assumes that denticle accumulation rates correlate with shark abundances. Here, we test this assumption by comparing the denticle record in surface sediments to three conventional shark survey methods at Palmyra Atoll, Line Islands, central Pacific Ocean, where shark density is high and spatially heterogeneous.We generally found a significant positive correlation between denticle accumulation rates and shark abundances derived from underwater visual census, baited remote underwater video and hook and line surveys.Denticle accumulation rates reflected shark abundances, suggesting that denticle assemblages can preserve a signal of time‐averaged shark abundance in low‐energy coral reef environments. We offer suggestions for applying this tool to measure shark abundance over long time‐scales in other contexts. [ABSTRACT FROM AUTHOR]

Atmospheric CO2 levels have been rising due to an increase in anthropic activities and its implications over marine ecosystems are unprecedented. The present study focused on the effects of ocean acidification (OA) on key hematological parameters of the juvenile small‐spotted catsharks (Scyliorhinus canicula). Eggs were reared throughout the entire embryogenesis (~4 months) plus 5 additional months, in two experimental treatments (control: pCO2 ~ 400 μatm; and high CO2: pCO2 ~ 900 μatm, Δ −0.3 pH units). After blood collection, the following hematological parameters were evaluated: (a) normal blood cells count (erythrocytes, leukocytes, and thrombocytes), (b) presence of erythrocytes with nuclear abnormalities, and (c) erythrocyte nucleus to cytoplasmic ratio. Concomitantly, to determine the cardiac and hematopoietic conditions, the spleen and heart to body ratios were also assessed. The present findings indicate that the measured variables may not be affected by elevated pCO2 in this temperate species, as no significant differences were observed between treatments across all the endpoints tested. Nonetheless, it is worth mentioning a decreasing trend observed in a number of thrombocytes associated with OA, which should foster further investigation, regarding other aspects of their coagulation response. Along with OA, other stressors are expected to impact marine life, such as warming and hypoxia. Thus, future research should aim to investigate the cumulative effect of these stressors on hematological parameters in sharks. HIGHLIGHTS: Hematological parameters were evaluated in temperate sharks exposed to high CO2 (OA). Measured variables may not be affected by elevated pCO2, since no significant differences were observed between treatments. Although there was a decreasing trend observed in the number of thrombocytes associated with OA. [ABSTRACT FROM AUTHOR]

International trade in vulnerable marine species is regulated once they are listed in CITES Appendices (the Convention on International Trade in Endangered Species of Wild Fauna and Flora). Parties to the Convention submit proposal(s) 150 days prior to the CITES Conference for voting on the inclusion of new species in Appendices I and II, making a case for why CITES listing criteria are met in each case. Before the vote, Parties receive advice from (a) the Food and Agriculture Organization of the United Nations, (b) the International Union for Conservation of Nature—TRAFFIC and (c) the CITES Secretariat, among others. This paper offers an expert review of listing processes, which are the subject of much debate in fishery and environment‐protection communities, looking at two specific cases: silky shark (Carcharhinus falciformis, Carcharhinidae) and bigeye thresher shark (Alopias superciliosus, Alopiidae). The reviewers determine that the evidence made available to voting Parties is substantial, but suffers from non‐standard presentation across assessments. The best available data are not always presented or described transparently in relation to CITES criteria. An extension of the assessment period, as well as the opportunity to refute evidence, has been suggested as ways to support more informed and effective decision‐making by CITES Parties, whose composition of delegations varies greatly in their experience of marine species management and trade. Experts welcomed a greater coherence of advice between fishery and non‐fishery sources in the long term, and proposed a range of suggested improvements for the delivery of information and advice to CITES Parties. [ABSTRACT FROM AUTHOR]

Neonatal predation in multispecies aquarium exhibits can prevent detection of captive breeding by wobbegong sharks. We used ultrasonography and isolation strategies to prevent neonatal predation and maximize survival/growth of the dwarf ornate wobbegong (Orectolobus ornatus de Vis, 1883). We captured seven free‐living wobbegongs (two males and five females) and subjected each animal to a health assessment which led to the euthanasia of one female with a retained hook. Ultrasonography showed that females were pregnant, one was preovulatory, and one was in a resting phase. Two females (one pregnant) and one male were placed in isolation in each of two tanks. In October 2006, 25 neonates were born overnight with the two litters placed into separate neonate tanks. Over the ∼6.5‐month monitoring period, four neonates with reduced body condition died without premonitory signs resulting in a 63.0% annual survival rate. Finite growth rates did not differ between sexes or litters and averaged (±SE) 12.2 (1.5) cm/year and 156.4 (26.4) g/year. At the cessation of monitoring, total length had increased by ∼30%, whereas total weight had almost doubled with neonatal body condition in line with free‐living wobbegongs. Our efficacious, six‐step manipulative, the approach should be applicable with all wobbegongs given their reproductive similarities, but we recommend that efforts focus on the dwarf ornate, tasselled and Japanese wobbegongs because all are small in size and have bred in aquaria. Ultimately, this approach should produce self‐sustaining aquarium populations, place less reliance on the wild acquisition and provide animals for other aquaria, population restocking, or scientific research. HIGHLIGHTS: 1.Capture and isolation of pregnant wobbegongs from the main exhibit aquarium enables predation‐fre parturition. Continued isolation enables public exhibition of neonates and the monitoring of growth, survival and the effects of enhanced feeding regimes. [ABSTRACT FROM AUTHOR]

By examining the maturity of 283 black dogfish Centroscyllium fabricii from Greenland waters, a shift in size‐at‐maturity in both sexes over the past 25 years is observed. Size‐at‐first maturity decreased approximately 10 cm in both sexes, and L50 and L95 shifted similarly in males, but not in females. It is argued that bycatch in the Greenland halibut Reinhardtius hippoglossoides fishery has contributed to the observed shift, but also emphasised that such a distinct change could have a methodological component as well as being subject to effects of environmental change. [ABSTRACT FROM AUTHOR]