Eagle Ray Research Articles

A hydrodynamic antenna: novel lateral line system in the tail of myliobatid stingrays.

Eagle rays, cownose rays and manta rays (order Myliobatiformes) have a slender tail that can be longer than the animal's body length, but its function and structure are unknown. Using histology, immunohistochemistry and three-dimensional imaging with micro-computed tomography scans, we describe the anatomy and function of the tail in Rhinoptera bonasus, the cownose ray. The tail is an extension of the vertebral column with unique morphological specializations. Along the tail behind the barb, vertebral centra are absent and neural and haemal arches fuse to form a solid mineralized structure that we describe for the first time and term caudal synarcual, which imparts passive stiffness to the tail, reducing bending. Two lateral line canals connected to an extensive tubule network extend along both sides of the tail. Tubules branch from the lateral line canal toward the dorsal and ventral tail surfaces, opening to the surrounding water via pores. A continuous neuromast is located within each lateral line canal, maintaining an uninterrupted structure along the entire tail. The complex lateral line mechanosensory system in the tail of R. bonasus supports the hypothesis that the tail functions like a hydrodynamic sensory antenna and may play an important role in their behavioural and functional ecology.

Novel approach to studying marine fauna: using long-life remote underwater video cameras to assess occurrence and behaviour of threatened and data-deficient elasmobranch species in southern Mozambique

Understanding the behaviour and ecological role of elasmobranchs is essential for their conservation, particularly in regions harbouring threatened and data-deficient species like the Inhambane coastline in southern Mozambique, southwestern Indian Ocean. This study employed long-life remote underwater video cameras (LL-RUV) to observe elasmobranch occurrence and behaviour at a rocky reef near Praia do Tofo known for frequent elasmobranch sightings. Between 2021 and 2024, 524 hours of LL-RUV data were collected, revealing the presence of 14 threatened and data-deficient elasmobranch species. Reef manta rays (Mobula alfredi), small eye stingrays (Megatrygon microps), and oceanic manta rays (Mobula birostris) were identified as the primary elasmobranch users of the studied cleaning stations (n = 81, n = 72 and n = 61 respectively), engaging in mutualistic interactions with cleaner fish and spending significant amounts of time at the studied reef. In contrast, spotted eagle rays (Aetobatus narinari) and blacktip sharks (Carcharhinus limbatus) were solely observed cruising over the reef without engaging in cleaning interactions (n = 40 and n = 27 respectively). In addition, this study provides evidence of intra- and inter-specific interactions between reef and oceanic manta rays, small eye stingrays and bowmouth guitarfish (Rhina ancylostoma) and co-occurrences of both manta ray species and smalleye stingrays with “hitchhiker” species including cobia (Rachycentron canadum) and remoras (Echeneis spp.). The use of LL-RUV cameras represents a significant advancement in marine research. These cameras enable continuous, non-intrusive, long-term monitoring of marine environments, capturing natural behaviours, while minimising disturbances caused by divers. As a result, more accurate observations of elasmobranch behaviour and cleaning station dynamics can be recorded, which might be missed during short-term surveys. This research highlights the potential of LL-RUV cameras as powerful tools for advancing our understanding of elasmobranch occurrence and behaviour and underscores their value in informing targeted and effective conservation strategies. Beyond elasmobranch research, LL-RUVs hold tremendous potential for studying a wide range of marine species and habitats, offering a versatile tool for ecological monitoring and conservation efforts across diverse marine ecosystems.

Comparative feeding analysis between the Chilean eagle ray Myliobatis chilensis (Philippi, 1982) and the Peruvian eagle ray Myliobatis peruvianus (Garman, 1913) from northern Peru

This study analyzed the diets of eagle rays in northern Peru to understand their intraspecific and interspecific feeding patterns, as well as their roles in the marine ecosystem. We obtained 109 stomachs with contents from Chilean eagle ray Myliobatis chilensis and 81 from Peruvian eagle ray Myliobatis peruvianus, between December 2020 and November 2021 in northern Peru (6º47'54"S and 79º59'30"W, San Jose, Lambayeque). The results show that M. chilensis has a benthic-pelagic feeding behavior with 14 prey families identified in its diet. The Peruvian anchovy Engraulis ringens, unidentified polychaetes, and families Onuphidae, Sternaspidae, Opheliidae, among others preys, were identified. On the other hand, M. peruvianus consumed Nassariidae, unidentified mollusks, unidentified polychaetes, and Veneridae, among other preys. We also found that both rays are secondary consumers with a restricted diet breadth (Bi < 0.6), where M. chilensis showed significant differences in diet by season and size class, while M. peruvianus only by size class. This study provides new information about eagle rays and is the first study to compare their diets. Furthermore, it also provides evidence of trophic segregation; however, given some overlap of some prey groups, low ecological redundancy. Finally, this study provides key information for the conservation of eagle rays in an important marine ecosystem in the eastern Pacific Ocean.

Spatial ecology and philopatric tendencies of whitespotted eagle ray, Aetobatus narinari, in Cozumel, Mexico

Spatial ecology and philopatric tendencies of whitespotted eagle ray, Aetobatus narinari, in Cozumel, Mexico

Genetic Diversity, Kinship, and Polychromatism in the Spotted Eagle Ray Aetobatus ocellatus of Fiji

The spotted eagle ray Aetobatus ocellatus (Kuhl, 1923) has a widespread Indo-West Pacific distribution and displays substantial population genetic structuring. Genetic data are crucial for understanding the species’ diversity, connectivity, and adaptation. However, molecular genetic information on A. ocellatus from Melanesia is lacking, which impedes our understanding of gene flow among geographic regions. In this study, we sampled 45 A. ocellatus, primarily from Fiji’s largest fish market in the capital, Suva. Mitochondrial DNA Cytochrome C Oxidase subunit I (COI) barcoding was used for species identification, and DArT-seqTM technology was applied to assess the nuclear genetic diversity. Barcoding of the COI gene showed a 98.6% to 99.8% similarity to A. ocellatus reference sequences in the Barcode of Life Data System, and the 45 individuals were represented by three major evolutionary haplotype clusters. Genotyping resulted in 24,313 Single-Nucleotide Polymorphisms (SNPs) which were quality-filtered to 7094 SNPs per individual. The observed heterozygosity level was 0.310. The inbreeding coefficient was positive, and genotyping identified one full-sibling pair and one half-sibling pair from the 45 individuals. Additionally, eagle rays exhibit polychromatic patterns, and at least three ventral pattern variations were recorded in specimens from the market. Collectively, our main findings characterize the genetic profile of A. ocellatus in Fiji and can help to understand the diversification of this species within the region.

Citizen science highlights rare behaviours by the spotted eagle ray Aetobatus ocellatus Kuhl 1823

Citizen science highlights rare behaviours by the spotted eagle ray Aetobatus ocellatus Kuhl 1823

Assessing the vulnerability of Elasmobranch species in the Bay of Bengal: Insights from Lakkha gill net fishery of Bangladesh

The elasmobranch population is declining in the Bay of Bengal of Bangladesh due to large-mesh gill net fishing, locally known as the Lakkha net, which primarily targets Indian threadfin (Leptomelanosoma indicum). This study was the first attempt to identify megafaunal bycatch in Lakkha fishing and assess its vulnerability using Productivity Susceptibility Analysis. A total of 40 elasmobranch bycatch species were identified, with sharks comprising 13 species from three families, while 27 rays belonged to six families, with the majority belonging to the Myliobatiformes order (60 %). Productivity and susceptibility scores were assigned to all identified species, with values ranging from 1.27 to 2.73 and 1.50 to 2.63, respectively. The target Lakkha fish exhibited the highest susceptibility score, followed by several pelagic sharks and eagle rays. Vulnerability assessment revealed that 31.7 % (n = 13) of species were highly vulnerable, while 43.9 % (n = 18) were classified as moderate, and 24.4 % (n = 10) were considered to have low vulnerability. All the high-risk megafauna species (n = 13) are classified as threatened by the global IUCN Red List. Sensitivity analysis highlighted susceptibility as a major contributor to species’ vulnerability. Alterations in susceptibility scores led to significant changes in the vulnerability status of many species. The overall data quality assessment indicated moderate data quality across species, with variability observed between productivity (76 % of species received a poor data quality score) and susceptibility attributes. However, vulnerability of these species can be reduced through adequate gear modification, shorter net deployment periods, adoption of safe discharge techniques, identification of critical habitats, and establishment of marine protected areas within this region. This study provides valuable insights into the species composition and vulnerability of elasmobranchs in the Lakkha gill net fishery, emphasizing the need for conservation measures to mitigate bycatch impacts on threatened species.

The complete mitochondrial genome of the imperiled Bullnose ray Myliobatis freminvillei (Myliobatiformes: Myliobatidae) with comments on its phylogenetic position and claims of diversifying selection affecting protein coding genes in a closely related species

The Bullnose ray Myliobatis freminvillei is a bentho-pelagic eagle ray that inhabits the north Gulf of Mexico and the Western Atlantic Ocean Coast, discontinuously, from Massachusetts, USA to Buenos Aires, Argentina. Myliobatis freminvillei is currently listed as vulnerable by the 2019 IUCN Red List of Threatened Species given that it is often captured as bycatch by artisanal and commercial fisheries, along the coasts of Argentina, Brazil, and Venezuela. This study, for the first time, assembled and characterized the mitochondrial genome of M. fremnvillei. The A+T rich mitochondrial genome of M. fremnvillei is 18,356 bp long and encodes 22 transfer RNA genes (tRNA), 2 ribosomal RNA genes (12S ribosomal RNA and 16S ribosomal RNA), 13 protein coding genes (PCGs), and also contains a non coding control region 2,617 bp long. Nonsynonomous codon usage with a preference for A+T rich codons was observed in all 13 PCGs. Leu (CTA), Ile (ATC), Phe (TTC), Thr (ACA), and Ala (GCC) were the most frequently used codons. Ka/Ks ratios estimated for all 13 PCGs exhibited values < 1, indicating strong purifying selection affecting all these genes. In contrast to the results of a previous study that claimed diversifying selective pressure in two mitochondrial PCGs of Mobula tarapacana, reanalysis of the Ka/Ks values for the same species indicated purifying selection in all 13 PCGs. Of the 22 tRNA genes, all have a cloverleaf secondary structure except tRNA-Ser1 which has a truncated dihydrouridine arm. In the control region, A+T rich microsatellites (n = 42) and short tandem repeats (n = 6) were identified, and the secondary structure of the same region contained numerous hairpin loops. Phylomitogenomic analyses supported the monophyletic status of the order Myliobatiformes and family Myliobatidae. The assembled mitochondrial genome will assist with conservation efforts in Myliobatis fremnvillei.

Population Structure of Aetobatus narinari (Myliobatiformes) Caught by the Artisanal Fishery in Northeast Brazil

In Brazil, the Whitespotted Eagle Ray Aetobatus narinari is considered data-deficient due to the scarcity of basic information on its biology, ecology, and vulnerability to capture. Despite this, the species is caught by artisanal fishing along most of the coast, especially in the northeast of Brazil. This study analyzed mitochondrial DNA data in specimens of A. narinari caught by artisanal fishing in the northeast coast of Brazil to understand their population structure. For this, 42 individuals were sequenced at three mitochondrial genes: cytochrome oxidase 1 (COI), cytochrome b (Cytb), and NADH dehydrogenase subunit 4 (ND4). Concatenated COI-Cytb-ND4 sequences yielded 14 haplotypes, with moderate haplotype diversity (h = 0.646), low nucleotide diversity (π = 0.00087), and low fixation index ΦST values, indicating no population structure. Our results suggest that there is only one population of A. narinari in the study area. Genetic studies can contribute to improving management plans in these areas, avoiding the overexploitation of this and other species.

Persistent organic pollutants and chlorpyrifos in tissues of a histotrophic viviparous species, the Southern Eagle Ray Myliobatis goodei

Elasmobranchs are good indicators of marine pollution as they accumulate pollutants from water and food, and occupy different trophic levels. Concentrations of organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs) and chlorpyrifos were quantified in muscle, liver, gonads, gills, and brain in both sexes and maturity stages of the Southern Eagle Ray, Myliobatis goodei, captured in Argentine coastal waters. Moreover, possible histological alterations in the liver and gonads were analyzed. Pollutant concentrations were pervasive across all tissues, with PCBs > OCPs > chlorpyrifos. Elevated pollutant levels were notably found in the liver and gills. We identified thirty-six PCB congeners in tissues, with low-chlorine congeners prevailing. Among OCPs, ∑DDT and ∑endosulfan were predominant. Females exhibited higher pollutant levels in most tissues compared to males, except in the gonads, and adults generally displayed elevated pollutant levels. Histological analysis revealed the presence of atretic follicles and melanomacrophages (MM). Continuous monitoring of pollutant levels, alongside their effects on physiological and ecological traits, is imperative for effective management and conservation efforts.

The occurrences and reclassification of eagle ray Aetobatus flagellum (Bloch &amp; Schneider,1801) in Iraqi Marine waters

The species Aetobatus flagyllem was caught and reclassified in the Iraqi marine waters on board the boat Anwar 2, and from its specifications, 17 morphometric traits were calculated. The species contains three thorns to defend against prey. It is noted that some morphometric traits are close to each other after using the PCA analysis for some traits of the species from different environments.

Two new American species of Aberrapex (Eucestoda: Lecanicephalidea: Aberrapecidae) from myliobatid stingrays (Batoidea: Myliobatidae).

Here I describe Aberrapex panamensis sp. nov., a parasite of the rough eagle ray Aetomylaeus asperrimus from the eastern Pacific coast of Panama, and Aberrapex catarinensis sp. nov., found in Myliobatis goodei off southern coast of Santa Catarina, Brazil. Aberrapex panamensis sp. nov. is the second record of Aberrapex Jensen, 2001 for the eastern Pacific Ocean and A. catarinensis sp. nov. is the fifth species of the genus registered in southwestern Atlantic Ocean. The two new species are morphologically distinct from all their congeners. Aberrapex panamensis sp. nov. and A. catarinensis sp. nov. can be distinguished from the majority of their congeners by the microthrix pattern on the scolex surface, number of proglottids and testes, length and width of the scolex, uterus extension, and presence and extension of an external seminal vesicle. The description of these two new species of lecanicephalideans expands the knowledge of this cestode order, with A. panamensis sp. nov. being the third species of the genus reported from Aetomylaeus Garman, and A. catarinensis sp. nov. being the sixth species of Aberrapex reported from Myliobatis Cuvier.

Multi-method approach identifies a South African estuary as an important elasmobranch habitat and potential nursery ground

Elasmobranchs play important ecological roles but are highly threatened. Understanding their habitat use and abundance is crucial for the management and conservation of these species and their habitats. While some species are known to use estuaries as vital habitats (e.g. feeding or nursery grounds), this remains an understudied area. A multi-method approach was used to survey the Keurbooms Estuary on the south coast of South Africa, over two years, to quantify the diversity, relative abundance and habitat use of elasmobranchs in this system. The survey methods were baited remote underwater video (BRUV), boat-based visual sightings, and unmanned aerial video (UAV). Opportunistic sightings were also collected. Six elasmobranch species were observed, with significant differences in community composition between the methods. Whereas effort was skewed towards BRUV surveys, the boat and UAV surveys recorded more elasmobranchs more frequently, and opportunistic sightings recorded the highest diversity. The common eagle ray Myliobatis aquila was the most abundant elasmobranch species and the only one recorded year-round; most individuals (93%) were juveniles, suggesting the Keurbooms Estuary may be a nursery area for this Critically Endangered species. The duckbill ray Aetomylaeus bovinus and common smoothhound shark Mustelus mustelus were observed during summer, the latter forming large aggregations. Another three ray species were recorded rarely. This study highlights the benefit of using a multi-method survey approach for shallow ecosystems and reveals the Keurbooms Estuary as an important habitat for elasmobranchs.

Spatiotemporal abundance of the whitespotted eagle ray and the giant manta ray (Chondrichthyes: Myliobatiformes) from aerial surveys in southeast Florida

Spatiotemporal abundance of the whitespotted eagle ray and the giant manta ray (Chondrichthyes: Myliobatiformes) from aerial surveys in southeast Florida

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.

Spots of trouble: shedding light on the species complex of eagle rays (Aetobatus) along eastern tropical Pacific, Cocos Island’s case

The eagle ray (Aetobatus) species complex has undergone several reassessments in previous decades. We present photographic evidence that supports the possible existence of a second species of Aetobatus in the eastern tropical Pacific. Broader morphological and molecular assessment is needed to reevaluate the distribution ranges of species in Aetobatus.

Mating sanctuary for whitespotted eagle rays (Aetobatus narinari) in Brazilian southeastern waters

Mating sanctuary for whitespotted eagle rays (Aetobatus narinari) in Brazilian southeastern waters

Marine megafauna interactions with the Peruvian artisanal purse-seine fleet

Bycatch is a global problem for marine megafauna. Peru is a major fishing nation known in particular for its industrial purse-seine fishery for the Peruvian anchovy (Engraulis ringens). However, Peru also has an artisanal purse-seine fishery for this same resource and other species such as Pacific bonito (Sarda chiliensis), Pacific chub mackerel (Scomber japonicus) and Chilean jack mackerel (Trachurus murphyi) used for human consumption. While there is limited documentation of bycatch of megafauna by the industrial purse-seine fishery, there is no similar information for the artisanal purse-seine fishery. Therefore, this study aimed to assess the marine megafauna (small-cetaceans, seabirds, sea turtles, and elasmobranchs) bycatch interactions of the Peruvian artisanal purse-seine fishery for consumption for the year 2019 (before the COVID-19 pandemic) through interviews with artisanal fishers in 5 landing ports (San Jose, Santa Rosa, Callao, Pucusana, and San Andres). We found that these fisheries had bycatch with all taxa groups, with dusky dolphins (Lagenorhynchus obscurus), guanay cormorants (Leucocarbo bougainvilliorum) and eagle rays (Myliobatis spp.) having the highest quantity and most frequently reported bycatch. Multiple correspondence analysis (MCA) indicated an association between the bycatch of 1–3 common dolphins (Delphinus spp.) per set from the northern ports (San Jose and Santa Rosa) and vessels of 20–36 MT. Likewise, a relationship was found between smooth hammerhead sharks (Sphyrna zygaena) and vessel storage capacity, with a similar result reported for the bycatch of humpback smoothhounds (Mustelus whitneyi). In addition, a relationship of eagle ray (Myliobatis spp.) bycatch with a landing port was identified, and several respondents mentioned catching more than 1 MT per set. Fifty-three percent of fishers considered bycatch to be a problem, mainly because it wastes their time during fishing operations. This preliminary study is the first research that demonstrates bycatch in artisanal purse-seine in Peru and can serve as a baseline for future research. We also highlight the need to quantify bycatch rates of marine megafauna using additional methodologies, such as monitoring with onboard observers.

Divergent mechanisms for crushing shelled prey in parallel lineages of durophagous stingrays (Myliobatoidei)

Durophagous vertebrates feed on shelled prey and share many morphological traits; in particular, high leverage jaws with robust jaw-closing muscles. Myliobatid stingrays are no exception, having reinforced jaw skeletons, large jaw adductor muscles, and with all species in the family consuming some combination of shelled prey. Myliobatid rays have a long evolutionary history (65–70 million years) and number over thirty species, yet despite similar performance demands given their diet ecology, exhibit considerable morphological diversity of the feeding apparatus. We examined how feeding performance changes in the bullnose ray, Myliobatis freminvillei over its ontogeny, and compared how these rays produce crushing bite forces relative to confamilial and co-occurring cownose rays (Rhinopterinae). Within the durophagous family Myliobatidae, rhinopterines are more generalist in their dietary preferences, feeding on small bivalves and infaunal crustaceans, whereas eagle rays (Aetobatinae) prey on gastropods and bivalves exclusively, while bullnose/bat rays (Myliobatinae) consume a size range of gastropods and hermit crabs. We found that bullnose rays show isometric changes in feeding performance over their ontogeny, relying on the high mechanical efficiency of their jaws to crush shelled prey throughout their ontogeny. This manner of generating high bite forces diverges from cownose rays and other durophagous elasmobranchs, which primarily rely on muscular hypertrophy to generate forceful bites. These two lineages evolved distinct means of dismantling hard prey, which further showcases how multiplicity of form can result in similar ecological function. These predators are frequently subsumed within a single ecological category, durophagy, which underestimates their diversity.

First insights into the population characteristics and seasonal occurrence of the great hammerhead shark, Sphyrna mokarran (Rüppell, 1837) in the Western Tuamotu archipelago, French Polynesia

The occurrence and seasonality of the Critically Endangered great hammerhead shark, Sphyrna mokarran, is data deficient in the Central Pacific region. Using photo-identification and laser-photogrammetry, we describe the seasonal population of great hammerhead sharks in the Tiputa pass (Rangiroa atoll) and Tuheiava pass (Tikehau atoll) in the Tuamotu archipelago of French Polynesia. During the austral summer of 2020 and 2021, we recorded a female-biased aggregation of at least 55 individuals (54 females; 1 unknown sex), representing an unprecedented number of S. mokarran in one study. All measured sharks were likely mature with pre-caudal lengths ranging from 147 cm to 297 cm (n = 35). Videos from citizen scientists recorded over a 15-year period enable us to identify 30 additional individuals between 2006 and 2019, with strong evidence of sexual segregation during the year. Our findings revealed seasonal residency (n = 32) of up to 6 days/month and for up to 5 months at the study site during the austral summer. We also demonstrated site fidelity with 32 individuals returning to the same atoll for up to 12 years between the first and last sighting, and with limited evidence of connectivity between the two sites. Our analysis also provides preliminary insight into the environmental factors driving S. mokarran aggregation in the Tiputa pass, suggesting a marked influence of the lunar cycle and of ocellated eagle rays (Aetobatus ocellatus) abundance. This study, conducted in situ with non-invasive methods offers a unique opportunity to study a great hammerhead shark population in a near-pristine ecosystem and provides important life-history elements for the Central Pacific region.