Batoid Species Research Articles

Elasmobranch Mark–Recapture Experiment off the Balearic Islands: Insight into Scyliorhinus canicula Growth, Mobility, and Population Size

Despite the high diversity of elasmobranch fishes in the Balearic Islands, knowledge of their biology and population dynamics is still scarce. A recent mark-and-recapture experiment off the Balearic Islands tagged 3738 individuals of 23 shark and batoid species during MEDITS and CANAL bottom trawl scientific surveys from June 2021 to August 2023. Retrieval was reported for the sharks Scyliorhinus canicula and Mustelus mustelus, revealing relatively small home ranges for these species (0.2–38.5 km and 7.8–15.3 km for S. canicula and M. mustelus, respectively). Recapture efficiency was higher from scientific surveys than from commercial catches, highlighting potential challenges in collaboration with fishermen and recapture reports. Density estimates obtained from the MEDITS bottom trawl survey suggest a much larger population for S. canicula than estimates from the mark–recapture data, indicating MEDITS density estimates for this species may be overestimated due to its scavenger behavior perhaps favoring individuals searching for discards aggregated in the fishing grounds. This study emphasizes the importance of monitoring, collaborative efforts, and improved reporting mechanisms to enhance our understanding of elasmobranch populations and provide support for sustainable management of these vulnerable marine species.

Vulnerability of Eastern Tropical Pacific chondrichthyan fish to climate change.

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.

Cranial musculature of batoids: A standardized nomenclature.

Batoids (rays and skates) are cartilaginous fishes whose jaws are not articulated directly to the neurocranium. The only point of contact between them are the hyomandibular cartilages, resulting in a unique mandibular suspension called euhyostyly. Due to this decoupling of the jaws from the skull, muscles play an essential role in modulating mandibular movements during the feeding process, especially during mandibular protrusion. The main objectives of our study were: (1) to examine the mandibular musculature of eight batoid species from different orders in the Batoidea and (2) establish a standardized musclulature terminology for future comparative myological studies in batoids. For each muscle bundle, the general characteristics of each cranial muscle were described and their origin and insertions were identified. The number of muscle bundles differed intraspecifically. On the dorsal surface, we reported the first evidence of the presence of the precranial muscle (PCM) in U. halleri, as well as the ethmoideo-parethmoidalis muscle (ETM) in R. velezi, P. glaugostigma and Z. exasperata; in addition, the insertion of the spiracularis muscle (SP) extended to the ventral surface of the oropharyngeal tract in myliobatiforms. On the ventral surface of the head, both N. entemedor and M. californica exhibited additional muscles in the mandibular area. These muscles were renamed as part of the standardization of mandibular terminology: the depressor mandibularis minor (DMM) in N. entemedor and the adductor mandibulae profundus (AMP) in M. californica. The standardization of terminology is essential for futures studies of the mandibular apparatus in batoids, to facilitate the morphological description of muscles in species without anatomical accounts and for continuity in broader comparative analyses.

Age Readings and Assessment in Coastal Batoid Elasmobranchs from Small-Scale Size-Selective Fishery: The Importance of Data Comparability in Multi-Specific Assemblages

The large variation in vertebral shape and calcification observed among elasmobranch species prevents using a single method for enhancing growth bands and reading age. Further, estimating age and growth parameters can be difficult or impractical when samples are incomplete due to the bycatch of a size-selective fishery. Using a single and rapid method, age readings were obtained on the vertebrae of four batoid species, namely 53 individuals of Dasyatis pastinaca, 51 of Raja asterias, 15 of Torpedo marmorata, and 55 specimens of Torpedo torpedo, from the local small-scale trammel net fishery in the coastal waters (5–20 m depth) of the Central Tyrrhenian Sea during 2019–2021. Based on these data, a statistical routine was developed to obtain multiple estimates of age and growth parameters for incomplete samples due to size-selective fishing. The acceptable agreement between and within readers (intra and inter-reader disagreement < 5%) and the rate of increase in vertebral size with body size (differently ranked across species) demonstrated the consistency of the enhancing method. The parameters estimated by the Von Bertalanffy and Gompertz growth models matched the data available in the Mediterranean Sea for the species studied, with D. pastinaca, T. torpedo, and R. asterias showing the lowest (k = 0.05–0.12), intermediate (k = 0.112–0.19), and highest (k = 0.18–0.23) growth rates, respectively, in line with the life history traits of these species. Overall, the method proved effective both in delineating band pairs in vertebrae of different species and in reliably estimating the age and growth parameters of problematic samples due to size-selective fishing. The proposed method supports the collection of comparable demographic data from other areas where similar multi-specific assemblages are bycatch of size-selective fisheries impacting potential nursery areas and other essential habitats for elasmobranchs.

Correction: Dietary and niche analyses of four sympatric batoid species of the subtropical South Atlantic Ocean

Correction: Dietary and niche analyses of four sympatric batoid species of the subtropical South Atlantic Ocean

Dietary and niche analyses of four sympatric batoid species of the subtropical South Atlantic Ocean

Dietary and niche analyses of four sympatric batoid species of the subtropical South Atlantic Ocean

Rays in the Shadows: Batoid Diversity, Occurrence, and Conservation Status in Fiji.

Over recent decades, elasmobranchs (sharks, rays, and skates) have been increasingly recognized among the world's most threatened marine wildlife, leading to heightened scientific attention. However, batoids (rays and skates) are relatively understudied, especially in Large Ocean States of the Pacific. This synthesis compiles insights on batoid diversity and occurrence in Fiji's waters by integrating a literature review, participatory science programs such as the Great Fiji Shark Count (GFSC) Initiative, Projects Abroad Fiji (PA), Manta Project Fiji (MPF), and iNaturalist, along with environmental DNA. Nineteen batoid species from seven families were identified: 19 species from the literature, 12 from participatory science programs, and six from eDNA analysis. Notably, this study provides the first photographic evidence for the bentfin devil ray (Mobula thurstoni, Lloyd, 1908) in Fiji. GFSC data indicated the highest species diversity in the Western Division, with spotted eagle rays (Aetobatus ocellatus, Kuhl, 1823) and maskrays (Neotrygon sp.) being observed most. In-person interviews conducted by PA provided information on the occurrence of wedgefishes and potentially sawfishes. MPF records and iNaturalist uploads were dominated by reef manta rays (M. alfredi, Krefft, 1868), while the pink whipray (Pateobatis fai, Jordan and Seale, 1906) yielded the most DNA sequences. Overall, 68.4% of the species face an elevated extinction risk based on the International Union for the Conservation of Nature Red List criteria. Although caution is warranted with older literature-based records for the giant guitarfish (Glaucostegus typus, Anonymous [Bennett], 1830), giant stingaree (Plesiobatis daviesi, Wallace, 1967), and the lack of sawfish verification, this synthesis highlights the effectiveness of a combined methodological approach in establishing a reference point for the diversity and occurrence of this understudied taxon in Fiji.

Network Analysis Reveals Species-Specific Organization of Microbial Communities in Four Co-Occurring Elasmobranch Species along the Georgia Coast

Comparing co-occurring species may provide insights into how aspects of ecology may play a role in influencing their microbial communities. During the 2019 commercial shrimp trawl season off coastal Georgia, swabs of skin, gills, cloaca, and gut were taken for three species of batoids (Butterfly Ray, Bluntnose Stingray, and Atlantic Stingray) and one shark species (Atlantic Sharpnose) for high-throughput sequencing of the V4 region of the bacterial 16S rRNA gene. White muscle was analyzed for stable isotopes (δ13C and δ15N) to evaluate potential niche overlap in these four sympatric mesopredators. Significant differences were found in both δ13C and δ15N signatures across species, suggesting a degree of resource partitioning. When examined within tissue type, the host species had a weak effect on β-diversity for cloaca and skin, with no differences found for gill and gut samples. However, network analysis metrics demonstrated a stronger species-specific effect and distinct microbial community relationships were apparent between the shark and batoids, with the former having tighter networks for both internally- and externally-influenced tissues (gut/cloaca and skin/gills, respectively). Despite overlapping habitat use, species’ microbiomes differed in their organizational structuring that paralleled differences in stable isotope results, suggesting a mediating role of species-specific ecology on bacterial microbiomes.

Chondrichthyan fishes from the Middle Eocene Osinovaya Formation of Rostov Region, Russia

ABSTRACT A new chondrichthyan assemblage comprising 27 genera is described from the Middle Eocene Osinovaya Formation of the Bystraya River Basin, Morozovsk District of Rostov Region, in the southern part of European Russia. The Morozovsk assemblage consists of 21 genera and 24 species of shark, 5 genera and species of batoid and a single genus and species of chimaeroid fish (Edaphodon sp.). A composition of the assemblage is characterised by the coexistence of Otodus sokolovi, O. auriculatus, Isurolamna bajarunasi, Macrorhizodus praecursor, Jaekelotodus trigonalis and Brachycarcharias lerichei and indicates the Lutetian age of the deposits (possibly middle – upper Lutetian because of the presence of O. sokolovi together with O. auriculatus). This corresponds to the previous dating of the Osinovaya Formation. Lamniformes (12 taxa) and Myliobatiformes (5 taxa) are dominated in assemblage between elasmobranchs, characterising the inner to middle neritic warm-water environments. The Morozovsk elasmobranch assemblage belongs to the European paleobiogeographic region and shows a great similarity with the previously known coeval assemblages from the Western Europe, as well as with Uzbek assemblages from the adjacent Crimean-Caucasian paleobiogeographic region. Scarce data on chimaeroid fishes show that only the genus Edaphodon is rarely present in shallow-water environments and only in the European paleobiogeographic region.

Chondrichthyan systematics in Brazil depicted: historical overview, research trends and future perspectives

Abstract Brazil comprises one of the world’s biodiversity hotspots of the chondrichthyan fauna, currently with 12 orders, 44 families, 90 genera and over 200 species of sharks, batoids, and chimaeras. These species inhabit marine, estuarine and freshwater realms of coastal and oceanic zones from the North equatorial central to the South-western Atlantic Ocean. Reporting on species occurrence in Brazil goes back to the pre-Linnaean Period. The golden era of the European Zoological studies put in place the knowledge on the local fauna with many Brazilian endemic and native species being officially described. The birth of Ichthyology in Brazil in the early 20th century, however, represents the milestone for the Chondrichthyan Systematics in the country when national scientists published the first list of species. This study provides an historical overview of the Chondrichthyan Systematics research in Brazil through a literature review of peer-reviewed publications in shark taxonomy, phylogenetics and morphology. Scientific trends of over 120-year period of dedicated investigations are herein pointed out regarding research scope and subject area, methodology, target study taxa, and gender diversity. Research recommendations and priorities are further given to assist researchers and interested stakeholders on future efforts in shark science and conservation in the country.

Trophic assessment of three sympatric batoid species in the Southern Gulf of California.

The competitive exclusion principle establishes that the coexistence of closely related species requires a certain degree of resource partitioning. However, populations have individuals with different morphological or behavioral traits (e.g., maturity stages, sexes, temporal or spatial segregation). This interaction often results in a multi-level differentiation in food preferences and habits. We explored such resource partitioning between and within three batoid species: Hypanus dipterurus, Narcine entemedor, and Rhinoptera steindachneri in the southern Gulf of California, Mexico, using a combination of stomach content (excluding R. steindachneri) and stable isotope analyses. We found a clear differentiation between H. dipterurus and N. entemedor, where the latter exhibited more benthic habitats, supported by a greater association to infaunal prey and higher δ13C values. Though the degree and patterns of intra-specific segregation varied among species, there was a notable differentiation in both sex and stage of maturity, corresponding to changes in specialization (i.e., isotopic niche breadth) or trophic spectrum (varying prey importance and isotopic values per group). This work is a promising step towards understanding the dietary niche dynamics of these species in a potentially important feeding area within the southern Gulf of California, as well as the biological and ecological mechanisms that facilitate their coexistence.

Preliminary study on antimicrobial activities of skin mucus fromby-catch of Elasmobranch species

Skates and rays, which are widely encountered in the by-catch of fisheries activities from the Sea of Marmara and banned for sale by regulation, are species that are discarded if caught. For this reason, in our study, we aimed to determine the bioactive potentials of these species, considered fishing waste, by investigating the skin secretions and microbial flora. In our study, both the skin flora and mucus contents of the discarded species Dasyatis pastinaca (Linnaeus,1758), Myliobatis aquila (Linnaeus, 1758), and Raja clavata (Linnaeus, 1758) caught in the Sea of Marmara were investigated to determine their potential antimicrobial activities. A total of 164 bacteria were isolated from the epidermal mucus of the three batoid species. Antibacterial activity was observed from three isolated bacteria against Escherichia coli, Vancomycin-resistant Enterococcus faecium, E. faecalis, and Bacillus subtilis. Additionally, the highest antibacterial activity was observed for skin mucus of R. clavata. Mouse fibroblast cell viability was challenged with mucus secretions. M. aquila and R. clavata mucus secretions exhibited no observable change after 24 and 48 hours. The assays indicated that both the isolates and the skin mucus have potential antimicrobial activity against opportunistic pathogens.

Batoid fishery in Peru (1950-2015): Magnitude, management and data needs

Historical landings from the Food and Agriculture Organization (1950–2015) were used to estimate the contribution of the Peruvian batoid fishery to the eastern Pacific Ocean, and species-specific landings from Instituto del Mar del Peru (1997-2015) were used to identify the most-landed species, their landings sites and monthly variation throughout the year, and fishing gear types most used. The regulatory and research landscape were evaluated toward identifying potential gaps that may be hindering conservation and management of batoids in Peru. Results showed that in the eastern Pacific, Peru ranked second, after Chile, for batoid landings from 1950 to 2015. Of the twenty-three species of marine batoids that interact with Peruvian fisheries, the most landed taxonomic groups, from 1997 to 2015, were: Myliobatis spp. (i.e., M. chilensis and M. peruvianus; 45% of batoids landings), Mobula spp. (primarily M. mobular, and secondarily M. thurstoni, M. munkiana, M. tarapacana; 28%), Pseudobatos planiceps (6%), and Hypanus dipterurus (6%). Most of these species are landed in northern Peru, where gillnets are the most-used fishing gear to capture them. Batoid landings occurred year-round; yet, for H. dipterurus and P. planiceps landings were highest during the austral summer. Only three management measures exist for batoids fisheries in Peru for three species (i.e., M. birostris, Pristis pristis, Rhinoptera steindachneri) and two taxa (i.e., Mobula and Myliobatis) which are not fully enforced. Batoid research in Peru is limited, with only 25 publications from 1978 to 2022, in which the most studied species are Mobula birostris, M. chilensis and M. peruvianus. This study establishes an information baseline for batoids in Peru that can help guide their management, research, and conservation.

Trophic ecology of three sympatric batoid species (Dasyatis pastinaca, Raja clavata, and Raja maderensis) from the Azores, NE Atlantic

Trophic ecology of three sympatric batoid species (Dasyatis pastinaca, Raja clavata, and Raja maderensis) from the Azores, NE Atlantic

Ensamble de batoideos costeros en el norte del Perú: Conocimiento preliminar

This preliminarily study aims at increasing our understanding of an assemblage of coastal batoids on the northern coast of Peru by determining species composition, body size structure and its behaviour in Los Órganos bay, Piura. During 20 field trips in Los Organos Bay, Piura region, between the years 2016, 2017, and 2019, eighty-six individuals were sampled belonging to eight species: Zapteryx xyster (n= 22), Narcine entemedor (n= 11), Urobatis tumbesensis (n= 7), Urotrygon chilensis (n= 40), Pseudobatos planiceps (n= 1), Urobatis halleri (n= 1), Gymnura crebripunctata (n= 2), Aetobatus laticeps (n= 2). In the study area, a predominance of adult females was observed for Z. xyster, N. entemedor and U. chilensis. These preliminary results suggest that during the morning some batoid species (i.e., Z. xyster, N. entemedor, U. chilensis) use the coastal zone to rest since they are found inactive and partially or totally buried in the sand – N. entemedor could be also hunting through ambush. Future studies should determine if this is a gestation area for some of these batoid species.

Age, growth and maturity of the yellow stingray (Urobatis jamaicensis), a biannually reproductive tropical batoid.

Urobatis jamaicensis is a coastal batoid species affected by habitat loss and small-scale exploitation from fisheries and the aquarium trade, yet the life-history information available is limited. This is the first study to assess the vertebral centra from 195 stingrays to estimate age and growth patterns, and compare them with the biannual reproductive pattern previously reported for this species. Age-at-size data were compared using five different growth models and found a two-parameter von Bertalanffy growth function (VBGF), the Gompertz model and a modified VBGF fit best for males, females and sexes combined, respectively. Maturity was achieved before 1 year. However, growth did not cease with the onset of maturity, but instead slowed down. Results from marginal increment analysis and edge analysis indicated a nonannual somatic growth pattern with influences from the biannual reproduction cycle where peaks in resource allocation may be focused on ovulation rather than growth during March when larger brood sizes are present, while resources may be allocated more towards growth during August and September when brood sizes are generally smaller. These results may be used as a proxy for species with similar reproductive patterns or for those that lack annual or seasonal growth patterns.

Advancing DNA Barcoding to Elucidate Elasmobranch Biodiversity in Malaysian Waters.

The data provided in this article are partial fragments of the Cytochrome c oxidase subunit 1 mitochondrial gene (CO1) sequences of 175 tissues sampled from sharks and batoids collected from Malaysian waters, from June 2015 to June 2022. The barcoding was done randomly for six specimens from each species, so as to authenticate the code. We generated barcodes for 67 different species in 20 families and 11 orders. DNA was extracted from the tissue samples following the Chelex protocols and amplified by polymerase chain reaction (PCR) using the barcoding universal primers FishF2 and FishR2. A total of 654 base pairs (bp) of barcode CO1 gene from 175 samples were sequenced and analysed. The genetic sequences were blasted into the NCBI GenBank and Barcode of Life Data System (BOLD). A review of the blast search confirmed that there were 68 valid species of sharks and batoids that occurred in Malaysian waters. We provided the data of the COI gene mid-point rooting phylogenetic relation trees and analysed the genetic distances among infra-class and order, intra-species, inter-specific, inter-genus, inter-familiar, and inter-order. We confirmed the addition of Squalus edmundsi, Carcharhinus amboinensis, Alopias superciliosus, and Myliobatis hamlyni as new records for Malaysia. The establishment of a comprehensive CO1 database for sharks and batoids will help facilitate the rapid monitoring and assessment of elasmobranch fisheries using environmental DNA methods.

Contrasting the reproductive potential of Narcine entemedor and Rhinoptera steindachneri: 2 viviparous batoid species with different reproductive strategies

Narcine entemedor and Rhinoptera steindachneri are 2 viviparous batoid species of commercial importance on the Pacific coast of Mexico. However, no adequate management plan has been set forth for either of them to ensure sustainable use. The aims of this study were to assess the reproductive potential and the potential rate of population increase (rʹ) of both species, as well contrasting their reproductive strategies, to infer how susceptible they are to fishing exploitation. Comparatively, among batoids, N. entemedor females have an early age at maturity, relatively high fecundity, and an intermediate lifespan, while R. steindachneri females have an early age at maturity, low fecundity, and a relatively short lifespan. According to our estimates, however, both species have relatively high reproductive potential, which N. entemedor exhibits by investing energy in maximizing fecundity and R. steindachneri by increasing the embryo’s body mass. Therefore, N. entemedor has better capacity to recover from relatively high overfishing (rʹ = 0.48) in comparison with R. steindachneri (rʹ = –0.18). The methodology used in this study proved to be a good option to assess the risk of overfishing in species for which there is limited data.

Depredation of spanner crabs (Ranina ranina) by endangered batoids off the east coast of Australia

Cryptic mortality in fisheries relates to the unobserved or unrecorded mortality in a target ecosystem and is an important aspect of harvest management for fishery managers. Depredation is a key, observable form of cryptic mortality that relates to predators consuming a targeted species being caught within a fishing industry. This is of particular interest to the Queensland spanner crab fishing industry, where additional unobserved or unrecorded mortality through depredation of catch could be restricting current efforts to rebuild the population. High-resolution cameras were deployed on 178 baited tangle-nets (dillies) to investigate cryptic mortality, species interactions, and depredation within the spanner crab Ranina ranina fishery in Queensland, Australia. Physical parameters including current speed, temperature, depth, and time of soak were recorded. Depredation events were observed in the fishery by two species of endangered batoid species, the bowmouth guitarfish Rhina ancylostoma and wedgefish Rhynchobatus spp. However, rates of depredation in the fishery were low, with only 3.82% of crabs depredated. Fishing losses were calculated by comparing the total crabs on retrieval of a dilly, against total crabs observed while still soaking (MaxN) and at the beginning of retrieval. Overall, there was a loss of 37% in potentially harvested crabs through a combination of cryptic mortality and inefficient fishing practices. However, 27% of the losses could be reduced through shorter deployment times. We identified a significant correlation between the rate of depredation and current speed (∼0.6–0.8 knots), soak time and depth (<35 m). We also report spanner crab shell damage caused by mantis shrimp interactions, that likely contribute to an increase in spanner crabs discards due to unmarketable product. By identifying the species and drivers involved in spanner crab depredation, this study provides insights into ways that depredation events can be mitigated and managed.

Tracing Patterns and Biodiversity Aspects of the Overlooked Skates and Rays (Subclass Elasmobranchii, Superorder Batoidea) in Greece

Species belonging to the superorder Batoidea have been poorly assessed due to the lack of information on their life history aspects and their limited economic value. This work presents an overview of skates and rays inhabiting the marine Greek waters and reports biodiversity issues requiring resolution for conservation purposes. Overall, 30 species from nine families and 16 genera have been documented within the past 22 years, based on the available literature and technical reports from research surveys of the Hellenic Centre for Marine Research (HCMR). However, 28 species are currently confirmed, since the presence of two rajids has not been sufficiently demonstrated and hence is considered as doubtful. Recent changes in nomenclature allowed us to replace old with new names in four species on the Greek list; patterns in the frequency of occurrence were observed and species were assigned into five categories; and diversity and misidentification issues were reported by family. Although Greek waters are oligotrophic and not considered a biodiversity hot spot for elasmobranchs, a high number of batoid species is documented in the area; therefore, the need to reinforce knowledge on biological aspects of skates and rays, define their status and identify their main threats is essential.