Manta and devil ray species occurrence and distribution in Venezuela, assessed through fishery landings and citizen science data.

Manta and devil rays (collectively mobulids) belong to the monogeneric Mobulidae, which currently comprises 10 species, including a putative third manta ray species (Mobula cf. birostris). These large planktivorous rays are distributed throughout the tropical and subtropical oceans of the world. To date, six mobulid species are reported for the western Atlantic Ocean and the Caribbean Sea, three of which had previously been reported in Venezuela (Mobula birostris, Mobula tarapacana and Mobula hypostoma). A preliminary assessment of fishery landings and citizen science data was conducted to further the scientific knowledge of mobulid species in Venezuela. Fisheries landing data were collected at Margarita Island between 2006 and 2007, and again in 2014. Data mining of internet search engines and social media platforms spanning the past two decades was also conducted. A total of 117 individuals of five mobulid species were recorded: Mobula sp. (n = 27), M. birostris (n = 36), M. tarapacana (n = 3), Mobula mobular (n = 26), Mobula thurstoni (n = 14) and M. cf. birostris (n = 11). The latter three species are the first confirmation of these species in Venezuela. The authors found no records of the previously reported M. hypostoma during this study. Although the occurrence of M. hypostoma in Venezuela remains possible because of the broad regional range of this species, its current presence in Venezuela is invalidated given the repeated misidentifications which have occurred in previous publications. The results of this study increase the number of reported mobulid ray species in Venezuela to five (excluding M. hypostoma). The overall data from juvenile manta rays and pregnant M. mobular and M. thurstoni recorded in this study, combined with the occurrence of all but one species of mobulid ray found in the western Atlantic Ocean, suggest Venezuela provides important habitat for this threatened family of rays.

Pupil dilation and constriction in the skate Leucoraja erinacea in a simulated natural light field.

The skate Leucoraja erinacea has an elaborately shaped pupil, whose characteristics and functions have received little attention. The goal of our study was to investigate the pupil response in relation to natural ambient light intensities. First, we took a recently developed sensory-ecological approach, which gave us a tool for creating a controlled light environment for behavioural work: during a field survey, we collected a series of calibrated natural habitat images from the perspective of the skates' eyes. From these images, we derived a vertical illumination profile using custom-written software for quantification of the environmental light field (ELF). After collecting and analysing these natural light field data, we created an illumination set-up in the laboratory, which closely simulated the natural vertical light gradient that skates experience in the wild and tested the light responsiveness - in particular the extent of dilation - of the skate pupil to controlled changes in this simulated light field. Additionally, we measured pupillary dilation and constriction speeds. Our results confirm that the skate pupil changes from nearly circular under low light to a series of small triangular apertures under bright light. A linear regression analysis showed a trend towards smaller skates having a smaller dynamic range of pupil area (dilation versus constriction ratio around 4-fold), and larger skates showing larger ranges (around 10- to 20-fold). Dilation took longer than constriction (between 30 and 45 min for dilation; less than 20 min for constriction), and there was considerable individual variation in dilation/constriction time. We discuss our findings in terms of the visual ecology of L. erinacea and consider the importance of accurately simulating natural light fields in the laboratory.

Changes in rays' swimming stability due to the phase difference between left and right pectoral fin movements.

Swimming motions of rays that swim using undulation locomotion are not always symmetrical; there may be a phase difference between the left and right pectoral fins. However, few studies on the swimming of rays have mentioned left and right pectoral fin movements. Moreover, the effects of movements of the left and right pectoral fins on swimming have not been clarified. This paper describes a computational study of phase differences of pectoral fin movements in the swimming of rays with the validity of fluid analysis methods. The movement and shape of the ray were made based on previous biological research and pictures. An overset grid was used to reproduce the ray's complex motions. The analysis was performed under four phase difference conditions: 0 [Formula: see text] ([Formula: see text] is the period), 0.25 [Formula: see text], 0.5 [Formula: see text], and 0.75 [Formula: see text]. The results show that a phase difference between the left and right pectoral fin movements affects swimming stability and maneuverability but not propulsive efficiency. We suggest that the phase difference in pectoral fin movements is essential for the swimming of rays, and rays adjust the phase difference between the movement of the left and right pectoral fins to suit their purpose.

Insights into the behavioural responses of juvenile thornback ray Raja clavata to alternating and direct current magnetic fields.

As part of energy transition, marine renewable energy devices (MRED) are currently expanding in developed countries inducing the deployment of dense networks of submarine power cables. Concern has thus raised about the cable magnetic emissions (direct or alternating current) because of potential interference with the sensorial environment of magneto-sensitive species, such as sharks and rays. This study sought to assess the short-term behavioural responses of juvenile thornback rays (Raja clavata) (n = 15) to direct and alternating (50 Hz) uniform 450-µT artificial magnetic fields using 1 h focal-sampling design based on a detailed ethogram. Careful control of magnetic fields' temporal and spatial scales was obtained in laboratory conditions through a custom-made Helmholtz coil device. Overall, qualitative or quantitative behavioural responses of juvenile rays did not significantly vary between control vs. exposed individuals over the morning period. Nonetheless, rays under direct current magnetic field increased their activity over the midday period. Synchronisation patterns were also observed for individuals receiving alternating current exposure (chronologic and qualitative similarities) coupled with a high inter-individual variance. Further studies should consider larger batches of juveniles to address the effect of long-term exposure and explore the sensitivity range of rays with dose-response designs.

Aspectos reproductivos de la raya látigo Hypanus longus (Garman, 1880) de los desembarques de la pesca artesanal en el Pacífico de Guatemala / Reproductive aspects of the longtail stingray Hypanus longus (Garman, 1880) from the landings of the artisanal fishery in the Pacific of Guatemala

La raya látigo Hypanus longus, ha pasado de ser una especie de captura incidental a una especie objetivo en la pesca artesanal del Pacífico de Guatemala. Esta actividad es realizada sin considerar criterios biológicos esenciales para su aprovechamiento sostenible. Aunado a ello, H. longus es una especie sensible, presentando características biológicas como: madurez sexual tardía, ciclos reproductivos largos y baja fecundidad. El presente estudio contribuye al conocimiento de la biología reproductiva de la raya látigo. Durante mayo de 2019 a marzo de 2020 se realizaron 11 muestreos de los desembarques de la pesca artesanal en la comunidad de Sipacate, Escuintla, en cada muestreo se registró el ancho de disco (AD), el peso, sexo y estado de maduración sexual de H. longus. En total se registraron 336 organismos, que presentaron una proporción sexual de 1:1, un AD para hembras de M = 82.33 cm, DS = 22.24 y de M = 76.91 cm, DS = 11.86 para machos. A partir de las evaluaciones externas e internas de los aparatos reproductores se determinó la talla de madurez sexual (L50), siendo de 88.2 y 79.3 cm AD para hembras y machos respectivamente. Finalmente, este estudio evidencio que el 65.68% de hembras y el 52.10% de machos son capturados por debajo de la L50, por lo cual se recomienda elaborar e implementar estra-tegias o medidas tendientes a la regulación de las prácticas pesqueras o artes de pesca que permitan la captura de organismos mayores a 95 cm de AD.

The whip ray Hypanus longushas gone from being a bycatch species to a target species in artisanal fisheries in the Pacific of Guatemala. This activity is carried out without considering essential biological criteria for its sustainable use. In addition, H. longusis a sensitive species, presenting biological characteristics such as late sexual maturity, long reproductive cycles and low fecundity. The present study contributes to the knowledge of the reproductive biology of the whip ray. During May 2019 to March 2020, 11 samplings were conducted from artisanal fishery landings in the community of Sipacate, Escuintla, in each sampling the disc width (AD), weight, sex and sexual maturation stage of H. longus were recorded. A total of 336 organisms were recorded, which pre-sented a sex ratio of 1:1, with a female AD of M = 82.33 cm, SD = 22.24 and M = 76.91 cm, SD = 11.86 for males. From the external and internal evaluations of the reproductive apparatus, the size at sexual maturity (L50) was determined to be 88.2 and 79.3 cm AD for females and males, respectively. Finally, this study showed that 65.68% of females and 52.10% of males are caught below L50, so it is recommended to develop and implement strategies or measures to regulate fishing practices or fishing gear that allow the capture of organisms larger than 95 cm AD.

Hematology and blood biochemistry profile of the freshwater stingray Potamotrygon magdalenae as a tool for population assessment in artificial environments / Perfil hematológico e bioquímico do sangue da arraia de água doce Potamotrygon magdalenae como ferramenta para avaliação da população em ambientes artificiais

Hematological and blood biochemical reference information is important to establish physiological status of freshwater stingray populations and improve care and management protocols in artificial environments. Here, we used a commercial freshwater stingray with high mortality rates in the market (Potamotrygon magdalenae), as an example to understand how artificial environments and handling protocols influence physiological status of captive freshwater stingrays. To this purpose, blood from five adult males and six adult females was collected to perform complete blood counts and blood chemistry analyses. All sampled animals showed good body condition with no differences between sexes. Differences between sexes were only found for the differential count of lymphocytes. Red blood results were consistent with previously studied potamotrygonids while white blood results showed higher values of leukocytes, thrombocytes, heterophils and lymphocytes in P. magdalenae compared to other Potamotrygonids. All types of leukocytes described for elasmobranchs were found except neutrophils and basophils. Blood metabolites showed an influence of ex situ diet in total protein, triglycerides and cholesterol. Glucose results were consistent while urea showed lower levels than those recorded for other freshwater stingrays. These results highlight the importance of physical, physiological and health analysis in freshwater stingrays as a part of welfare assessment to improve monitoring protocols and survival rates in public or private aquaria.

A informação de referência hematológica e bioquímica do sangue é importante para estabelecer o estado fisiológico das populações de arraias de água doce e melhorar os protocolos de cuidado e manejo em ambientes artificiais. Aqui, usamos uma espécie comercial de arraia de água doce com elevadas taxas de mortalidade no mercado(Potamotrygon magdalenae) como espécie exemplo para compreender de que modo os ambientes artificiais e os protocolos de manipulação influenciam o estado fisiológico das arraias de água doce em cativeiro. Para este fim, foi coletado sangue de cinco machos adultos e seis fêmeas adultas para realizar contagens completas de células sanguíneas e análises bioquímicas de sangue. Todos os animais amostrados mostraram boa condição corpórea, sem diferenças entre os sexos. Diferenças entre os sexos foram encontradas só na contagem diferencial de linfócitos. Os resultados de células sanguíneas vermelhas foram consistentes com potamotrigonídeos previamente estudados, enquanto o leucograma revelou valores mais elevados de leucócitos, trombócitos, heterófilos e linfócitos em P. magdalenae, em comparação com outros potamotrigonídeos. Todos os tipos de leucócitos descritos para elasmobrânquios foram encontrados, exceto para neutrófilos e basófilos. Todos os tipos de leucócitos descritos para elasmobrânquios foram encontrados, exceto para neutrófilos e basófilos. Os metabólitos do sangue mostraram influência da dieta ex situ nas proteínas totais, triglicerídeos e colesterol. Os resultados da glicose foram consistentes, enquanto a ureia mostrou níveis mais baixos do que os registrados para outras espécies de arraias de água doce. Os resultados da glicose foram consistentes, enquanto a ureia mostrou níveis mais baixos em P. magdalenae. Estes resultados enfatizam a importância da análise física, fisiológica e de saúde em arraias de água doce como parte da avaliação do bem-estar para melhorar os protocolos [...].

hox gene expression predicts tetrapod-like axial regionalization in the skate, Leucoraja erinacea.

The axial skeleton of tetrapods is organized into distinct anteroposterior regions of the vertebral column (cervical, trunk, sacral, and caudal), and transitions between these regions are determined by colinear anterior expression boundaries of Hox5/6, -9, -10, and -11 paralogy group genes within embryonic paraxial mesoderm. Fishes, conversely, exhibit little in the way of discrete axial regionalization, and this has led to scenarios of an origin of Hox-mediated axial skeletal complexity with the evolutionary transition to land in tetrapods. Here, combining geometric morphometric analysis of vertebral column morphology with cell lineage tracing of hox gene expression boundaries in developing embryos, we recover evidence of at least five distinct regions in the vertebral skeleton of a cartilaginous fish, the little skate (Leucoraja erinacea). We find that skate embryos exhibit tetrapod-like anteroposterior nesting of hox gene expression in their paraxial mesoderm, and we show that anterior expression boundaries of hox5/6, hox9, hox10, and hox11 paralogy group genes predict regional transitions in the differentiated skate axial skeleton. Our findings suggest that hox-based axial skeletal regionalization did not originate with tetrapods but rather has a much deeper evolutionary history than was previously appreciated.

Evaluating artisanal fishing of globally threatened sharks and rays in the Bay of Bengal, Bangladesh.

Sharks and rays are at risk of extinction globally. This reflects low resilience to increasing fishing pressure, exacerbated by habitat loss, climate change, increasing value in a trade and inadequate information leading to limited conservation actions. Artisanal fisheries in the Bay of Bengal of Bangladesh contribute to the high levels of global fishing pressure on elasmobranchs. However, it is one of the most data-poor regions of the world, and the diversity, occurrence and conservation needs of elasmobranchs in this region have not been adequately assessed. This study evaluated elasmobranch diversity, species composition, catch and trade within the artisanal fisheries to address this critical knowledge gap. Findings show that elasmobranch diversity in Bangladesh has previously been underestimated. In this study, over 160000 individual elasmobranchs were recorded through landing site monitoring, comprising 88 species (30 sharks and 58 rays) within 20 families and 35 genera. Of these, 54 are globally threatened according to the IUCN Red List of Threatened Species, with ten species listed as Critically Endangered and 22 species listed as Endangered. Almost 98% juvenile catch (69-99% for different species) for large species sand a decline in numbers of large individuals were documented, indicating unsustainable fisheries. Several previously common species were rarely landed, indicating potential population declines. The catch pattern showed seasonality and, in some cases, gear specificity. Overall, Bangladesh was found to be a significant contributor to shark and ray catches and trade in the Bay of Bengal region. Effective monitoring was not observed at the landing sites or processing centres, despite 29 species of elasmobranchs being protected by law, many of which were frequently landed. On this basis, a series of recommendations were provided for improving the conservation status of the elasmobranchs in this region. These include the need for improved taxonomic research, enhanced monitoring of elasmobranch stocks, and the highest protection level for threatened taxa. Alongside political will, enhancing national capacity to manage and rebuild elasmobranch stocks, coordinated regional management measures are essential.

The bowfin genome illuminates the developmental evolution of ray-finned fishes.

The bowfin (Amia calva) is a ray-finned fish that possesses a unique suite of ancestral and derived phenotypes, which are key to understanding vertebrate evolution. The phylogenetic position of bowfin as a representative of neopterygian fishes, its archetypical body plan and its unduplicated and slowly evolving genome make bowfin a central species for the genomic exploration of ray-finned fishes. Here we present a chromosome-level genome assembly for bowfin that enables gene-order analyses, settling long-debated neopterygian phylogenetic relationships. We examine chromatin accessibility and gene expression through bowfin development to investigate the evolution of immune, scale, respiratory and fin skeletal systems and identify hundreds of gene-regulatory loci conserved across vertebrates. These resources connect developmental evolution among bony fishes, further highlighting the bowfin's importance for illuminating vertebrate biology and diversity in the genomic era.

A hitchhiker guide to manta rays: Patterns of association between Mobula alfredi, M. birostris, their symbionts, and other fishes in the Maldives.

Despite being among the largest and most charismatic species in the marine environment, considerable gaps remain in our understanding of the behavioural ecology of manta rays (Mobula alfredi, M. birostris). Manta rays are often sighted in association with an array of smaller hitchhiker fish species, which utilise their hosts as a sanctuary for shelter, protection, and the sustenance they provide. Species interactions, rather than the species at the individual level, determine the ecological processes that drive community dynamics, support biodiversity and ecosystem health. Thus, understanding the associations within marine communities is critical to implementing effective conservation and management. However, the underlying patterns between manta rays, their symbionts, and other hitchhiker species remain elusive. Here, we explore the spatial and temporal variation in hitchhiker presence with M. alfredi and M. birostris throughout the Maldives and investigate the factors which may influence association using generalised linear mixed effects models (GLMM). For the first time, associations between M. alfredi and M. birostris with hitchhiker species other than those belonging to the family Echeneidae are described. A variation in the species of hitchhiker associated with M. alfredi and M. birostris was identified, with sharksucker remora (Echeneis naucrates) and giant remora (Remora remora) being the most common, respectively. Spatiotemporal variation in the presence of manta rays was identified as a driver for the occurrence of ephemeral hitchhiker associations. Near-term pregnant female M. alfredi, and M. alfredi at cleaning stations, had the highest likelihood of an association with adult E. naucrates. Juvenile E. naucrates were more likely to be associated with juvenile M. alfredi, and a seasonal trend in E. naucrates host association was identified. Remora were most likely to be present with female M. birostris, and a mean number of 1.5 ± 0.5 R. remora were observed per M. birostris. It is hoped these initial findings will serve as the basis for future work into the complex relationships between manta rays and their hitchhikers.

Tracking the rising extinction risk of sharks and rays in the Northeast Atlantic Ocean and Mediterranean Sea.

The loss of biodiversity is increasingly well understood on land, but trajectories of extinction risk remain largely unknown in the ocean. We present regional Red List Indices (RLIs) to track the extinction risk of 119 Northeast Atlantic and 72 Mediterranean shark and ray species primarily threatened by overfishing. We combine two IUCN workshop assessments from 2003/2005 and 2015 with a retrospective backcast assessment for 1980. We incorporate predicted categorisations for Data Deficient species from our previously published research. The percentage of threatened species rose from 1980 to 2015 from 29 to 41% (Northeast Atlantic) and 47 to 65% (Mediterranean Sea). There are as many threatened sharks and rays in Europe as there are threatened birds, but the threat level is nearly six times greater by percentage (41%, n = 56 of 136 vs. 7%, n = 56 of 792). The Northeast Atlantic RLI declined by 8% from 1980 to 2015, while the higher-risk Mediterranean RLI declined by 13%. Larger-bodied, shallow-distributed, slow-growing species and those with range boundaries within the region are more likely to have worsening status in the Northeast Atlantic. Conversely, long-established, severe threat levels obscure any potential relationships between species' traits and the likelihood of worsening IUCN status in the Mediterranean Sea. These regional RLIs provide the first widespread evidence for increasing trends in regional shark and ray extinction risk and underscore that effective fisheries management is necessary to recover the ecosystem function of these predators.

Cartilage structure increases swimming efficiency of underwater robots.

Underwater robots are useful for exploring valuable resources and marine life. Traditional underwater robots use screw propellers, which may be harmful to marine life. In contrast, robots that incorporate the swimming principles, morphologies, and softness of aquatic animals are expected to be more adaptable to the surrounding environment. Rajiform is one of the swimming forms observed in nature, which swims by generating the traveling waves on flat large pectoral fins. From an anatomical point of view, Rajiform fins consist of cartilage structures encapsulated in soft tissue, thereby realizing anisotropic stiffness. We hypothesized that such anisotropy is responsible for the generation of traveling waves that enable a highly efficient swimming. We validate our hypothesis through the development of a stingray robot made of silicone-based cartilages and soft tissue. For comparison, we fabricate a robot without cartilages, as well as the one combining soft tissue and cartilage materials. The fabricated robots are tested to clarify their stiffness and swimming performance. The results show that inclusion of cartilage structure in the robot fins increases the swimming efficiency. It is suggested that arrangement and distribution of soft and hard areas inside the body structure is a key factor to realize high-performance soft underwater robots.

A lack of red blood cell swelling in five elasmobranch fishes following air exposure and exhaustive exercise.

In teleost fishes, catecholamine-induced increases in the activity of cation exchangers compensate for decreases in hemoglobin oxygen affinity and maximum blood oxygen carrying capacity caused by decreases in plasma pH (i.e., metabolic acidosis). The resultant red blood cell (RBC) swelling has been documented in sandbar (Carcharhinus plumbeus) and epaulette (Hemiscyllium ocellatum) sharks following capture by rod-and-reel or after a 1.5 h exposure to anoxia (respectively), although the underlying mechanisms remain unknown. To determine if RBC swelling could be documented in other elasmobranch fishes, we collected blood samples from clearnose skate (Rostroraja eglanteria), blacktip reef shark (Carcharhinus melanopterus), and sicklefin lemon shark (Negaprion acutidens) subjected to exhaustive exercise or air exposure (or both) and measured hematocrit, hemoglobin concentration, RBC count, RBC volume, and mean corpuscular hemoglobin content. We did likewise with sandbar and epaulette sharks to further explore the mechanisms driving swelling when present. We could not document RBC swelling in any species; although hematocrit increased in all species (presumably due to RBC ejection from the spleen or fluid shifts out of the vascular compartment) except epaulette shark. Our results indicate RBC swelling and associated ion shifts in elasmobranch fishes is not inducible by exercise or hypoxia, thus implying this response maybe of lesser importance for maintaining oxygen delivery during acute acidosis than in teleost fishes.

Coastal sharks and rays in a marine protected area in southern Brazil.

In southern Brazil, we investigated shark and ray capture records in an integral protection marine protection area (MPA) that allows fishing in that area. We found 10 shark and nine ray species, of which 88.5% and 66.2%, respectively, are endangered. Female adults and neonates of both sexes are abundant in the area, with records of stranding of large specimens, postcapture abortions and ovigerous capsules with fresh embryos on the beach. We suggest the application of continuous fisheries monitoring and an increase in guidelines on the capture of endangered species.

First insights into the vertical habitat use of the whitespotted eagle ray Aetobatus narinari revealed by pop-up satellite archival tags.

The whitespotted eagle ray Aetobatus narinari is a tropical to warm-temperate benthopelagic batoid that ranges widely throughout the western Atlantic Ocean. Despite conservation concerns for the species, its vertical habitat use and diving behaviour remain unknown. Patterns and drivers in the depth distribution of A. narinari were investigated at two separate locations, the western North Atlantic (Islands of Bermuda) and the eastern Gulf of Mexico (Sarasota, Florida, U.S.A.). Between 2010 and 2014, seven pop-up satellite archival tags were attached to A. narinari using three methods: a through-tail suture, an external tail-band and through-wing attachment. Retention time ranged from 0 to 180 days, with tags attached via the through-tail method retained longest. Tagged rays spent the majority of time (82.85 ± 12.17% S.D.) within the upper 10 m of the water column and, with one exception, no rays travelled deeper than ~26 m. One Bermuda ray recorded a maximum depth of 50.5 m, suggesting that these animals make excursions off the fore-reef slope of the Bermuda Platform. Individuals occupied deeper depths (7.42 ± 3.99 m S.D.) during the day versus night (4.90 ± 2.89 m S.D.), which may be explained by foraging and/or predator avoidance. Each individual experienced a significant difference in depth and temperature distributions over the diel cycle. There was evidence that mean hourly depth was best described by location and individual variation using a generalized additive mixed model approach. This is the first study to compare depth distributions of A. narinari from different locations and describe the thermal habitat for this species. Our study highlights the importance of region in describing A. narinari depth use, which may be relevant when developing management plans, whilst demonstrating that diel patterns appear to hold across individuals.

Photoreceptors in skate are arranged to allow for a broad horizontal field of view.

Studying retinal specializations offers insights into eye functionality and visual ecology. Using light microscopic techniques, including retinal whole-mounts, we investigated photoreceptor densities in the retina of the skate Leucoraja erinacea. We show that photoreceptors are not sized or oriented in the same way, and that they are not evenly distributed across the retina. There was a dorsally located horizontal visual streak with increased photoreceptor density, with additional local maxima in which densities were highest. Photoreceptors were longest and thinnest inside this visual streak, becoming shorter and thicker toward the periphery and toward the ventral retina. Furthermore, in the peripheral retinal parts, photoreceptors (particularly the outer segments) were noticeably tilted with respect to the retinal long axis. In order to understand how photoreceptors are tilted inside the eye, we used computerized tomography (CT) and micro-CT, to obtain geometrical dimensions of the whole skate eye. These CT/micro-CT data provided us with the outlines of the skate eye and the location of the retina and this enabled us to reconstruct how photoreceptors tilt in an intact eye. Findings were analyzed relative to previously published ganglion cell distributions in this species, showing a posteriorly located retinal area with photoreceptor: ganglion cell convergence as low as 39:1. Some peripheral areas showed ratios as high as 391:1. We frame our findings in terms of the animal's anatomy: body and eye shape, specifically the location of the tapetum, as well as the visual demands associated with lifestyle and habitat type. A speculative function in polarization sensitivity is discussed.

Reproductive biology of the Rasptail skate Rostroraja velezi (Rajiformes: Rajidae).

The Rasptail skate Rostroraja velezi is commercially exploited in artisanal elasmobranch fisheries along the west coast of Baja California Sur, Mexico, but information on its life history is limited. This study aimed to investigate the reproductive biology of R. velezi. A total of 105 specimens were caught from April 2008 to May 2012, including the largest reported specimen with 121 cm total length, 96 cm disc width (DW ). Females attained larger sizes than males. Males and females presented functional gonads. There was an asymmetry in the testes of males, with the left testis being larger. Histological analysis of the reproductive biology of R. velezi was performed here for the first time. The presence of sperm storage in females and spermatogenic development beginning at the first stages of maturity in males was recorded. It was possible to identify the development of secretions in the club, baffle and terminal zone of the oviducal gland. DW at maturity, defined as the DW at which 50% of the population is mature, was estimated at 68-72 cm for females and 65.1 cm for males. Egg-bearing females caught in April and May presented one egg capsule per uterus. Furthermore, a description of the egg capsule of R. velezi is provided. Elucidating the reproductive cycle, the type of reproductive strategies, and the fecundity of R. velezi will allow us to understand the impact of fisheries on this species.

Diet, trophic interactions and possible ecological role of commercial sharks and batoids in northern Peruvian waters.

The Peruvian sea represents one of the most productive ocean ecosystems and possesses one of the largest elasmobranch fisheries in the Pacific Ocean. Ecosystem-based management of these fisheries will require information on the trophic ecology of elasmobranchs. This study aimed to understand the diet, trophic interactions and the role of nine commercial elasmobranch species in northern Peru through the analysis of stomach contents. A total of 865 non-empty stomachs were analysed. Off northern Peru, elasmobranchs function as upper-trophic-level species consuming 78 prey items, predominantly teleosts and cephalopods. Two distinctive trophic assemblages were identified: (a) sharks (smooth hammerhead shark Sphyrna zygaena, thresher shark Alopias spp. and blue shark Prionace glauca) that feed mainly on cephalopods in the pelagic ecosystem; and (b) sharks and batoids (Chilean eagle ray Myliobatis chilensis, humpback smooth-hound Mustelus whitneyi, spotted houndshark Triakis maculata, Pacific guitarfish Pseudobatos planiceps, copper shark Carcharhinus brachyurus and school shark Galeorhinus galeus) that feed mainly on teleosts and invertebrates in the benthonic and pelagic coastal ecosystem. This study reveals for the first time the diet of T. maculata and the importance of elasmobranchs as predators of abundant and commercial species (i.e., jumbo squid Dosidicus gigas and Peruvian anchovy Engraulis ringens). The results of this study can assist in the design of an ecosystem-based management for the northern Peruvian sea and the conservation of these highly exploited, threatened or poorly understood group of predators in one of the most productive marine ecosystems.

Electrosensory Impairment in the Atlantic Stingray, Hypanus sabinus, After Crude Oil Exposure.

Elasmobranchs are renowned for their extremely sensitive electrosensory system, which is used to detect predators, prey, and mates, and is possibly used for navigation. The proper functioning of the electrosensory system is thus critical to fitness. The objective of this study was to test whether exposure to crude oil impairs the electroreceptive capabilities of elasmobranch fishes. Electrosensory function was quantified from six stingrays before and after exposure to a concentration of oil that mimicked empirically measured concentrations along the coast of Louisiana following the Deepwater Horizon spill. Orientation distance (cm), and angle with respect to the dipole axis of a prey-simulating electric field were used to derive the electric field intensity that elicited a response. Oil exposed stingrays continued to exhibit feeding behavior, but they initiated orientations to prey-simulating electric fields from a significantly closer orientation distance. The mean orientation distance after oil exposure was 5.29 ± 0.41 SE cm compared to a pre-exposure orientation distance of 7.16 ± 0.66 SE cm. Stingrays required a mean electric field intensity of 0.596 ± 0.21 SE µV cm-1 to initiate a response after oil exposure, compared to a mean of only 0.127 ± 0.03 SE µV cm-1 in uncontaminated seawater. Oil exposed stingrays thus exhibited a response to a stimulus approximately 4.7 times greater than controls. Stingrays impacted by an oil spill appear to experience reduced electrosensory capabilities, which could detrimentally impact fitness. This study is the first to quantify the effects of crude oil on behavioral electrosensory function.

Catch composition and life history characteristics of sharks and rays (Elasmobranchii) landed in the Andaman and Nicobar Islands, India.

Detailed information on shark and ray fisheries in the Andaman and Nicobar Islands, India are limited, including information on the diversity and biological characteristics of these species. We carried out fish landing surveys in South Andamans from January 2017 to May 2018, a comprehensive and cost-effective way to fill this data gap. We sampled 5,742 individuals representing 57 shark and ray species landed from six types of fishing gears. Of the 36 species of sharks and 21 species of rays landed, six species of sharks (Loxodon macrorhinus, Carcharhinus amblyrhynchos, Sphyrna lewini, C. albimarginatus, C. brevipinna, and Paragaleus randalli) comprised 83.35% of shark landings, while three species of rays (Pateobatis jenkinsii, Himantura leoparda and H. tutul) comprised 48.82% of ray landings, suggesting a species dominance in the catch or fishing region. We provide insights into the biology of species with extensions in maximum size for seven shark species. Additionally, we document an increase in the known ray diversity for the islands and for India with three previously unreported ray species. We found that amongst sharks, mature individuals of small-bodied species (63.48% males of total landings of species less than 1.5 m total length when mature) and immature individuals of larger species (84.79% males of total landings of species larger than 1.5 m total length when mature) were mostly landed; whereas for rays, mature individuals were predominantly landed (80.71% males of total landings) likely reflecting differences in habitat preferences along life-history stages across species and fishing gear. The largest size range in sharks was recorded in landings from pelagic longlines and gillnets. Further, the study emphasizes the overlap between critical habitats and fishing grounds, where immature sharks and gravid females were landed in large quantities which might be unsustainable in the long-term. Landings were female-biased in C. amblyrhynchos, S. lewini and P. jenkinsii, and male-biased in L. macrorhinus and H. leoparda, indicating either spatio-temporal or gear-specific sexual segregation in these species. Understanding seasonal and biological variability in the shark and ray landings over a longer study period across different fisheries will inform future conservation and fishery management measures for these species in the Andaman and Nicobar Islands.