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Global marine biodiversity declines require bold and ambitious plans to safeguard ecosystem services. Overfishing, habitat loss and projected climate impacts have yielded deleterious effects on marine predators, in particular, driving increasing threat of extinction for many shark species with implications for ecosystem health. Identifying and protecting critical habitat areas for sharks is fundamental to their protection, and may allow for species recovery. Here we use baited remote underwater video stations to investigate spatial and temporal patterns of habitat use by sharks in a Special Area of Conservation (SAC) that is centrally important to the regional blue economy in the UK, the Cardigan Bay SAC. Our results show heterogeneous spatial habitat use and temporal trends in habitat sharing between smallspotted catsharks Scyliorhinus canicula and nursehounds S. stellaris. Nearshore reef habitats are substantially more important than non-reef habitats for both species. The relative abundance of each species, however, is roughly inversely seasonally proportional, with S. canicula and S. stellaris relative abundance highest in March and September, respectively. Temporal niche partitioning may be an important mechanism in marine systems, but has not been widely investigated in sympatric shark communities. These findings are directly relevant for ongoing development of the Welsh Marine Evidence Strategy (2019-2025) and the Welsh National Marine Plan, particularly to inform spatial planning to strengthen the role of SAC management design in protecting important shark areas. [ABSTRACT FROM AUTHOR]

Age and growth estimates are essential for life historymodeling in elasmobranchs and are used to informaccurate conservation andmanagement decisions. The nurse shark (Ginglymostoma cirratum) is abundant in coastal waters of the Atlantic Ocean, yet many aspects of their life history remain relatively understudied, aside from their reproductive behavior.We usedmark-recapture data of 91 individual G. cirratum from Bimini, The Bahamas, from 2003 to 2020, to calculate von Bertalanffy (vB) growth parameters, empirical growth rate, and age derived from the resulting length-at-age estimates. The Fabens method for estimating growth from mark-recapture methods was applied through a Bayesian framework using Markov chain Monte Carlo (MCMC) methods. This provided growth parameters with an asymptotic total length (L∞) of 303.28 cm and a growth coefficient (k) of 0.04 yr-1. The average growth rate for G. cirratum was approximately 8.68 ± 6.00 cm yr-1. This study also suggests that the previous maximum age for G. cirratum is likely underestimated, with the oldest individual predicted to be 43 years old. Our study is the first to present vB growth parameters and a growth curve for G. cirratum. It indicates that this species is slowgrowing and long-lived, which improves our understanding of their life history. [ABSTRACT FROM AUTHOR]

Effective management and conservation of threatened species biodiversity requires knowledge of reproductive biology, such as cyclicity, mode, and age at maturity. We combined reproductive endocrinology and in-situ ultrasonography to examine reproductive characteristics of female Caribbean reef sharks Carcharhinus perezi, a widely distributed, threatened marine predator which remains largely understudied throughout its range. Unique to this study was the opportunity to conduct longitudinal assessments of two individuals, recaptured across multiple seasons during sampling in The Bahamas. Within- individual, paired hormone analyses and in-situ ultrasounds of female sharks that were confirmed as either pregnant, non-pregnant, or reproductively active, suggest a biennial reproductive cycle for Carcharhinus perezi. This unique opportunity to assess the reproductive biology of the same individuals over time underscore the importance of repeated sampling for elucidating population reproductive cyclicity of highly mobile sharks in the wild. [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]

Manta and devil rays (Mobulids) face several immediate threats, including incidental capture in industrial tropical tuna fisheries. As a result, efforts have emerged to avoid or mitigate Mobulid bycatch in these fisheries. However, many mitigation efforts fail to incorporate fisher expertise from the outset, potentially leading to interventions that are not viable. Here, we combine survey and focus group data to synthesize knowledge of Mobulid bycatch and mitigation ideas in Eastern Pacific Ocean purse seine fisheries. Primary obstacles for mitigating Mobulid bycatch, according to respondents, are: (1) an inability to sight Mobulids before capture, (2) the lack of specific equipment on board, and (3) the difficulty of releasing large individuals; we suggest that the latter two can be addressed by simple operational modifications. We also find that Mobulids are most likely to be sighted by fishers after capture, suggesting that this is an important time in the fishing operation for bycatch mitigation interventions that ensure Mobulids survive capture. To address this, we share creative ideas brought by fishers for avoidance of Mobulids. This study provides a model of how to incorporate stakeholder input in the design of bycatch technology in large-scale fisheries and could inform similar efforts around the world. [ABSTRACT FROM AUTHOR]

A new species of softnose skate, Bathyraja chapmani n. sp., is described from two female specimens collected in deepwater off Lima, Peru (-11.933°, -78.15°), in the southeastern Pacific, at 1714 m deep, in a fishery for Patagonian toothfish. The new species is separated from other southeastern Pacific Bathyraja species by having the same color and same irregular spotted pattern on both the dorsal and ventral surfaces, as well as the form and arrangement of thorns and denticles and several meristic characters. Bathyraja chapmani n. sp. has a uniform black-to-chocolate or dark-plum-brown background coloration with an irregular pattern of whitish to darkcolored scattered spots. Its closest congener, Bathyraja aguja, also from Peru, has two symmetrically arranged, large, white spots on the dorsal surface at the pectoral-fin bases, symmetrically arranged white spots along the disc margins, and a ventral surface lacking any spots or patterning. The new species is the fourth Bathyraja species known to occur in Peruvian waters. [ABSTRACT FROM AUTHOR]

There is currently a limited understanding of the morphological and functional organization of the olfactory system in cartilaginous fishes, particularly when compared to bony fishes and terrestrial vertebrates. In this fish group, there is a clear paucity of information on the characterization, density, and distribution of olfactory receptor neurons (ORNs) within the sensory olfactory epithelium lining the paired olfactory rosettes, and their functional implications with respect to the hydrodynamics of incurrent water flow into the nares. This imaging study examines the brownbanded bamboo shark Chiloscyllium punctatum (Elasmobranchii) and combines immunohistochemical labeling using antisera raised against five G-protein α-subunits (Gαs/olf, Gαq/11/14, Gαi–1/2/3, Gαi–3, Gα o ) with light and electron microscopy, to characterize the morphological ORN types present. Three main ORNs ("long", "microvillous" and "crypt-like") are confirmed and up to three additional microvilli-bearing types are also described; "Kappe-like" (potential or homologous "Kappe" as in teleosts), "pear-shaped" and "teardrop-shaped" cells. These morphotypes will need to be confirmed molecularly in the future. Using X-ray diffusible iodine-based contrast-enhanced computed tomography (diceCT), high-resolution scans of the olfactory rosettes, olfactory bulbs (OBs), peduncles, and telencephalon reveal a lateral segregation of primary olfactory inputs within the OBs, with distinct medial and lateral clusters of glomeruli, suggesting a potential somatotopic organization. However, most ORN morphotypes are found to be ubiquitously distributed within the medial and lateral regions of the olfactory rosette, with at least three microvilli-bearing ORNs labeled with anti-Gα o found in significantly higher densities in lateral lamellae [in lateral lamellae] and on the anterior portion of lamellae (facing the olfactory cavity). These microvilli-bearing ORN morphotypes (microvillous, "Kappe-like," "pear-shaped," and "teardrop-shaped") are the most abundant across the olfactory rosette of this species, while ciliated ORNs are less common and crypt cells are rare. Spatial simulations of the fluid dynamics of the incurrent water flow into the nares and within the olfactory cavities indicate that the high densities of microvilli-bearing ORNs located within the lateral region of the rosette are important for sampling incoming odorants during swimming and may determine subsequent tracking behavior. [ABSTRACT FROM AUTHOR]

Elasmobranchs contribute heavily to bycatch in longline fisheries globally, and an effective method of deterring them from baited fishing gear is needed. Electrosensory stimulus holds promise as a method of disrupting elasmobranch close-range feeding responses as their electric sense guides their final strike during prey capture. We used laboratory experiments to test the hypothesis that weak electric stimuli generated by a prototype electronic bycatch reduction device (BRD) could deter sandbar shark (Carcharhinus plumbeus) and spiny dogfish (Squalus acanthias) from eating bait. Voltage gradients <1 mV cm−1at the location of bait were produced by an Arduino microcontroller powered by a 9 V battery and attached to carbon electrodes. Median bait consumption by groups of juvenile sandbar shark declined by 74% when bait was located 10 cm vs. 2 m from active electrodes. Spiny dogfish median bait consumption halved when bait was located 10 cm from active vs. inactive electrodes. Although laboratory studies often produce a larger effect for electrosensory shark deterrents than can be demonstrated during field trials, if the effects seen in our laboratory studies produced similar effects in the field, it could meet fishermen's requirements for a BRD. [ABSTRACT FROM AUTHOR]

Elasmobranchs present four clasper movements, which can be seen in different contexts from mating to no obvious reason. Three movements have been reported in Carcharias taurus and here the first occurrence of clasper flaring in this species is described. Clasper flaring was observed while other species were in a reproductive state and their aggressive behaviour towards the subject of this study was also observed. [ABSTRACT FROM AUTHOR]

The ability to produce estimates of the metabolic rate of free-ranging animals is fundamental to the study of their ecology. However, measuring the energy expenditure of animals in the field has proved difficult, especially for aquatic taxa. Accelerometry presents a means of translating metabolic rates measured in the laboratory to individuals studied in the field, pending appropriate laboratory calibrations. Such calibrations have only been performed on a few fish species to date, and only one where the effects of temperature were accounted for. Here, we present calibrations between activity, measured as overall dynamic body acceleration (ODBA), and metabolic rate, measured through respirometry, for nurse sharks (Ginglymostoma cirratum), lemon sharks (Negaprion brevirostris) and blacktip sharks (Carcharhinus limbatus). Calibrations were made at a range of volitional swimming speeds and experimental temperatures. Linear mixed models were used to determine a predictive equation for metabolic rate based on measured ODBA values, with the optimal model using ODBA in combination with activity state and temperature to predict metabolic rate in lemon and nurse sharks, and ODBA and temperature to predict metabolic rate in blacktip sharks. This study lays the groundwork for calculating the metabolic rate of these species in the wild using acceleration data. [ABSTRACT FROM AUTHOR]

Bythaelurus naylori sp. n. is described based on 41 specimens collected from seamounts in the southwestern Indian Ocean. The new species can be separated from all other Bythaelurus species by a combination of distinctly enlarged dermal denticles on the upper caudal-fin margin, lack of papillae on the roof of the mouth and tongue, an anal-fin base length equal to or less than 1.5 times second dorsal-fin base length, and a uniformly plain medium to dark brown body coloration, with light fin edges and a distinct dark dusky-colored snout. No other Bythaelurus species has the combination of a caudal crest of prominent, distinctly enlarged, comb-like dermal denticles along the upper caudal margin and lacks oral papillae. Bythaelurus naylori sp. n. can be distinguished from its two closest congeners, B. giddingsi and B. lutarius, by a combination of prominent comb-like dermal denticles along the upper caudal-fin margin, absence of oral papillae, uniform body coloration, and noticeable dark dusky snout; Bythaelurus giddingsi has oral papillae present and a variegated color pattern, while B. lutarius lacks a caudal crest of enlarged denticles and matures at a much smaller size than the new species. [ABSTRACT FROM AUTHOR]

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