Understanding the breeding biology of endangered species, including breeding sex ratios (BSRs) and relative contributions of breeders to the next generation, is important for assessing population resiliency. Determining BSRs is especially relevant for species with temperature-dependent sex determination, such as marine turtles, to track potential shifts in BSRs driven by climate change. However, complex oceanic life cycles for marine turtles hinder research on individuals and life stages beyond nesting beaches, resulting in a comparative paucity of information regarding breeding males. Here, we estimated the BSR and described mating behavior for Eastern Caribbean (EC) hawksbill turtles Eretmochelys imbricata by reconstructing paternal genotypes with genetic assays of nesting females and their hatchlings at Jumby Bay, Antigua. We genotyped 821 hatchlings from the nests of 23 females with 5 microsatellite markers and generated paternal identities with a maximum-likelihood full-pedigree reconstruction program. Overall, 24 discrete male genotypes were reconstructed from the nests of 23 females, suggesting an even within-season BSR. We found single paternity for the nests of 21 out of 23 females (91.3%) and multiple paternity for the remaining 2 females (8.7%), with primary paternal contributions of 57 and 80%, respectively. One male sired the clutches of 2 different females, providing evidence of polygyny. Finally, fathers identified from the second nests of 6 females matched the fathers identified from first nests, indicating no inter-nest mating occurred. Our results provide baseline data for EC hawksbills to track BSRs over time, and according to 'convenience polyandry', suggest a low density of breeding individuals in the region.

Knowledge of the dietary composition of Atlantic marlins, especially for recently acknowledged species such as roundscale spearfish (Tetrapturus georgii), is limited, as sample access is constrained by international quotas and intermittent landing rates. A series of annual offshore recreational fishing tournaments target Atlantic blue marlin (Makaira nigricans), white marlin (Kajikia albida) and roundscale spearfish on their seasonal foraging grounds in the South and Mid-Atlantic Bight. Through this network of tournaments and recreational anglers, we collected stomachs from Atlantic blue marlin (n = 32), white marlin (n = 35) and roundscale spearfish (n = 44) from 2018 to 2020 to investigate general diet composition. Stomach content analysis and DNA barcoding identified a total of 16 prey families across the three focal species, but the majority of prey weight (%W) was from two families (Scombridae and Ommastrephidae). Blue marlin and roundscale spearfish were predominantly piscivorous (99.0 and 80.6%W fishes, respectively), whereas white marlin mainly consumed cephalopods (80%W). The contribution of Scombridae was highest for blue marlin (94.6%W), intermediate for roundscale spearfish (51.7%W) and lowest for white marlin (11%W), with an inverse pattern of relative contribution for Ommastrephidae (0.9, 16.1 and 73.9%W, respectively). Roundscale spearfish and white marlin, despite having a near identical morphology, had diets composed of different prey types in our sample. These dietary data, from three epipelagic apex predators, provide important information for wider ecosystem-based studies, including in relation to the Mackerel, Squid and Butterfish Fishery Management Plan overseen by the Mid-Atlantic Fishery Management Council.

Due to continued overexploitation and anthropogenic change, hammerhead sharks (Carcharhiniformes: Sphyrnidae) have experienced drastic declines over most of their geographic range. Owing to the K-selected life histories of these sharks, their population resilience and persistence, remain severely strained, further compromising ecosystem stability. Moreover, some species are largely understudied e.g. the cryptic congener, the Carolina hammerhead shark (Sphyrna gilberti), whilst specific regions, such as the South-West Indian Ocean (SWIO), remain relatively devoid of data, risking the eventual extirpation of unique hammerhead shark lineages. The aim of the present study was to verify the phylogenetic placement of the cryptic S. gilberti within the family Sphyrnidae through the inclusion of underrepresented species sequences in order to provide a more comprehensive phylogenetic perspective for understanding historical drivers of Sphyrnidae biodiversity. The present study describes the first complete mitochondrial genome of the cryptic S. gilberti originating from the US Atlantic, as well as the mitogenomes of smooth hammerhead shark (Sphyrna zygaena) and scalloped hammerhead shark (Sphyrna lewini) samples originating from the data deficient South-West Indian Ocean (SWIO). Furthermore, we estimate the phylogenetic interrelationships of the Sphyrnidae family using mitochondrial protein-coding (PCG) and rRNA genes, reaffirming the placement of S. gilberti as a sister lineage to S. lewini. The resulting phylogenetic estimate is further used to evaluate the most likely age of the first occurrence of S. gilberti, corresponding to the Late Miocene to Early Pleiocene Epoch (3.8-10.8 million years ago). Comparative analysis of these Sphyrnids between ocean basins, as well as preliminary divergence estimates for S. lewini and S. gilberti has contributed towards resolving the global hammerhead phylogeny. This has provided unique insights into the evolution of the genus, thereby aiding future efforts directed towards effective conservation and management of hammerhead populations over a larger spatial scale.

The commercially important Atlantic bluefin tuna (Thunnus thynnus), a large migratory fish, has experienced notable recovery aided by accurate resource assessment and effective fisheries management efforts. Traditionally, this species has been perceived as consisting of eastern and western populations, spawning respectively in the Mediterranean Sea and the Gulf of Mexico, with mixing occurring throughout the Atlantic. However, recent studies have challenged this assumption by revealing weak genetic differentiation and identifying a previously unknown spawning ground in the Slope Sea used by Atlantic bluefin tuna of uncertain origin. To further understand the current and past population structure and connectivity of Atlantic bluefin tuna, we have assembled a unique dataset including thousands of genome-wide single-nucleotide polymorphisms (SNPs) from 500 larvae, young of the year and spawning adult samples covering the three spawning grounds and including individuals of other Thunnus species. Our analyses support two weakly differentiated but demographically connected ancestral populations that interbreed in the Slope Sea. Moreover, we also identified signatures of introgression from albacore (Thunnus alalunga) into the Atlantic bluefin tuna genome, exhibiting varied frequencies across spawning areas, indicating strong gene flow from the Mediterranean Sea towards the Slope Sea. We hypothesize that the observed genetic differentiation may be attributed to increased gene flow caused by a recent intensification of westward migration by the eastern population, which could have implications for the genetic diversity and conservation of western populations. Future conservation efforts should consider these findings to address potential genetic homogenization in the species.

Historic over-exploitation and the more recent threats caused by fisheries by-catch, disease and climate change have left sea turtle populations in the Wider Caribbean at risk of extinction. In 1995, following regional declines in nesting and foraging populations, the island of Anguilla implemented a moratorium on the hunting of turtles. At the request of the Government of Anguilla for scientific data to either support or remove the moratorium, comprehensive population estimates were obtained, and foraging, nesting and migratory movements were examined. In addition, community perspectives on turtles and their protection were assessed. Between 2015 and 18 surveys of 30 nesting beaches estimated low nesting activity with a maximum of 41 hawksbill, 15 green, and 1-2 leatherback turtles nesting in Anguilla annually. The inter-nesting range of hawksbills exhibited high levels of geographic overlap and occurred within 1.5 km of nesting beaches. Migratory tracks of hawksbill turtles traversed through seven exclusive economic zones, two of which allow a legal turtle fishery. Site fidelity was observed in foraging areas of green turtles and genetic analysis revealed population differentiation between green turtle foraging sites in Anguilla and between hawksbill rookeries in Anguilla compared to other Leeward Islands, indicating the individual importance of each foraging and nesting site. The Anguillan public (n = 302) overwhelmingly agreed with the current ban on harvesting sea turtles and considered turtles important for ecotourism. Our work provides a case-study, that can be applied globally, of how scientific research combined with community perspectives can effectively inform policy and ultimately protect endangered species, and highlights that local Governments provided with high quality data in a timely fashion for their policy making timetable are more likely to integrate findings into their decision-making process.

Context Fourier transform near-infrared spectroscopy (FT-NIRS) is of interest to fisheries managers for rapid age prediction in fish otoliths, yet the underlying prediction mechanism is unknown. Aims To better understand drivers of FT-NIRS age prediction, we evaluated FT-NIRS spectra and age prediction models for otoliths of red snapper, Lutjanus campechanus, related to otolith structure, mass, and constituents (calcium carbonate (CaCO3) and protein). Methods Spectra were collected from a set of whole otoliths (n = 84, 0–28 years) and again sequentially after grinding to powder and subsampling a fixed mass of each ground otolith. Protein content was also measured (n = 26) and related to spectra. Key results Age prediction was diminished in ground and fixed-mass otolith models, but remained within 2 years of traditional ages. Protein content (0.43–0.92% weight) increased significantly with age, implying a concomitant decrease in CaCO3 content. FT-NIRS models predicted protein content to within 0.04%, but protein variability hindered modelling. Spectral characteristics of both CaCO3 and protein are evident in otolith spectra and are implicated in age-prediction models. Conclusions Changes in otolith composition, mass, and structure underlie FT-NIRS age prediction, but compositional changes inform the majority of age prediction. Implications These results provide a foundation for understanding FT-NIRS age prediction.

The geographic specificity of natal philopatry (how precisely breeding individuals return to their natal origins) influences breeding biology, genetic diversity and habitat range, and therefore has important implications for species resiliency and management. Also, the age at which individuals reach sexual maturity and enter the breeding population is a vital parameter for demographic analyses. Empirical research on philopatry and maturation, however, is challenging for long‐lived animals that are difficult to observe, such as marine turtles that have complex oceanic life histories. Regional natal philopatry is well established for marine turtles, but the geographic specificity of philopatry is unclear. Similarly, estimates of age at maturity vary widely, and direct evidence is lacking. Here, we targeted these information gaps by assessing kinship among 256 females from Antigua’s Jumby Bay (JB) hawksbill turtle rookery, a population with demonstrated nest‐site fidelity and neophyte assimilation. We estimated mother–daughter and full sibling relationships with a maximum‐likelihood full‐pedigree reconstruction approach, incorporating genotypic (12 microsatellites), maternal genealogy (mitochondrial DNA) and age structure (long‐term mark–recapture) data. We validated relationships with parentage assignment and pairwise relatedness estimators. Fourteen veteran nesters were the mothers of 42 younger nesters, and 94 nesters formed 35 full sibships. Time between the first nesting records of mothers and their daughters indicated maximum time to maturity as short as 14 years in Caribbean hawksbills. Thirteen of the 14 mothers showed consistently high fidelity to JB for two decades, providing compelling evidence that 41 of these daughters originated from JB nests and returned to this 1‐km‐long natal site to breed. Rookeries with strongly philopatric individuals might have limited colonization potential and be at a disadvantage in the event of habitat loss. This study demonstrates the utility of long‐term mark–recapture data in kinship analyses for answering questions relevant to endangered species conservation.

Environmental variation influences fish assemblage structure; however, fish assemblage composition shifts due to natural or anthropogenic stressors have been observed in marine ecosystems worldwide, altering ecosystem structure and function, and fisheries sustainability. Previous research in waters off North and South Carolina (USA) was limited in scope and repeatability or did not quantify fish assemblages at a scale suitable for monitoring composition shifts. Concurrent chevron traps, underwater video, and environmental data from an annual fishery-independent survey were used to characterize the environment and enumerate demersal reef fishes caught in the traps, and priority fish species observed in video in depths ~15-110 m. Multivariate analyses detected assemblage patterns and environmental influences. An 8-variable (distance to shelf edge, depth, consolidated substrate size, latitude, percent biotic cover, temperature, undercut height, biotic class) model predicted assemblages, while 4 variables explained the greatest variation (distance to shelf edge [19%], depth [15%], consolidated substrate vertical relief [4%], size [4%]). The largest number of discriminator species occurred in mid- to outer shelf areas with greater substrate complexity (i.e. increasing substrate size and relief). Assemblages dominated by Centropristis striata at depths (~15-40 m) with little substrate complexity transitioned towards assemblages dominated by Pagrus pagrus , higher prevalence of larger-bodied predators, and invasive Pterois spp. at depths (~40-110 m) with greater substrate complexity. Understanding baseline assemblage characteristics and natural drivers of variability in fish assemblage structure is vital to conservation and management efforts that monitor changes in population abundance, the presence/absence of key species, and stressor-induced modifications of local assemblages, which are all measures of ecological health that underpin comprehensive assessments and management.

Legacies of ancient riverine systems are often manifest in patterns of genetic diversity within aquatic species. The ancient Teays River, a principal drainage of the eastern United States, engaged in several ephemeral connections with neighboring palaeodrainages prior to and during the Pleistocene, when cyclical glacial advance and retreat reconfigured the region's fluvial systems. This study assayed DNA-sequence diversity at one mitochondrial (mtDNA) and three single-copy nuclear DNA (scnDNA) loci from the Tonguetied Minnow (Exoglossum laurae), a species distributed as four disjunct populations, one each within the Upper Great Miami, Upper Allegheny, Upper Genesee, and New rivers. Mitochondrial DNA variation revealed that the New River harbors the highest diversity (h = 0.73) and that the Tonguetied Minnow is composed of two ancient lineages, a Teays River lineage and a Pittsburgh River lineage. Analyses of the scnDNA loci revealed sharing of alleles among populations of E. laurae and between the Tonguetied Minnow and its only congener, the Cutlip Minnow (E. maxillingua), sampled from the Roanoke and Potomac rivers. The probability of interspecific hybridization in the New and Upper Genesee rivers was estimated as 0.16 and 0.34, respectively, but it is likely that some degree of incomplete lineage sorting contributed to these estimates. Probabilities of interspecific hybridization for Cutlip Minnow were 0.62 and 0.65, for the Roanoke and Potomac rivers, respectively, and might reflect ancient hybridization resulting from stream capture events involving these drainages by the Teays River. Management strategies should focus on maintaining the security of the Pittsburgh River lineage in the Upper Great Miami and Upper Allegheny River drainages. Finally, insights into the Tonguetied Minnow's rather convoluted taxonomic history are few, but genetic variation is inconsistent with subspecies status for Tonguetied Minnow in the Upper Great Miami River drainage.

Loss of wetlands throughout the southeastern United States threatens the persistence of the region's highly diverse freshwater fauna. Losses are especially concerning for rare species that maintain small or fragmented ranges, zoogeographies that characterize many of the region's numerous freshwater endemics. We assayed nuclear and mitochondria' DNA sequence data from the Pine Barrens Treefrog (Hyla andersonii), a rare species distributed across the Atlantic and Gulf coastal plains. We hypothesized that the species' evolutionary history has been associated with changes in wetlands during Quaternary interglacials and that the contemporaneous extent of wetlands is positively correlated with population genetic diversity. Genetic variation was highest in North Carolina and South Carolina and lowest in New jersey and Florida. Mean times to common ancestry ranged from 132,486 to 1,290,605 yr before present, and effective sizes ranged from 4,241 individuals in New Jersey to 403,718 individuals in North Carolina. Population migration rates were generally very low (<0.01), although higher rates were found between North Carolina and South Carolina. Total area of wetlands varied from 2,482 km(2) in South Carolina to 7,384 km(2) in North Carolina and has declined between 2001 and 2016. Genetic diversity was positively, although nonsignificantly, correlated to total amount of wetland habitat. Pine Barrens Treefrog is comprised of four relictual populations associated with ecological changes driven by climatic progressions of Quaternary interglacials, and collectively these populations conform to an abundant center model of evolution. All populations are conservatively designated management units, although evolutionarily significant unit status cannot be discounted.

Recent application of Fourier transform near infra-red spectroscopy (FT-NIRS) to predict age in fish otoliths has gained attention among fisheries managers as a potential alternative to costly production ageing of managed species. We assessed the age prediction capability of FT-NIRS scans in whole otoliths from red snapper, Lutjanus campechanus, collected from the US Gulf of Mexico and US Atlantic Ocean (South Atlantic). Otoliths were scanned with an FT-NIR spectrometer and resulting spectral signatures were regressed with traditionally estimated ages via partial least squares regression to produce calibration models, which were validated for predictive capability against test sets of otoliths. Calibration models successfully predicted age with R-2 ranging 0.94-0.95, mean squared error <= 1.8 years, and bias <0.02 years. Percent agreement between FT-NIRS and traditional ages was lower than within-reader agreement for traditional estimates, but average percent error was similar and Kolmogorov-Smirnov tests were not significantly different (p >= 0.06) between traditional and FT-NIRS predicted ages for optimal calibration models. Ages >31 years were not well predicted, possibly due to light attenuation in the thickest otoliths. Our results suggest that FT-NIRS can improve efficiency in production ageing for fisheries management while maintaining data quality standards.

Fourier Transform Near Infrared Spectroscopy (FT-NIRS) has shown great promise as a rapid and non-destructive method for predicting age in years from a variety of ageing structures in fish. Herein we assess the utility of FT-NIRS to predict both daily age and otolith weight from whole otoliths of juvenile red snapper Lutjanus campechanus collected from the US Gulf of Mexico and southeastern US Atlantic Ocean. Spectral data from whole otoliths (n = 153) were collected with a FT-NIR spectrometer while manipulating otolith presentation with an external aperture to maximize signal to noise. Traditional daily age estimates and otolith weights were correlated to spectral data via partial least-squares regression to create age and otolith weight prediction models that were compared across aperture treatments and geographic region. FT-NIBS calibration models using apertured spectra were significantly better at predicting age than models using non-apertured spectra (model rank = 5 and 10, respectively) and yielded predicted age to within an average of six days relative to traditional estimates (R-2 = 0.91, RMSECV = 6.08 days, bias = 0.04). Exponential growth models produced from FT-NIBS-predicted ages (L-t = 28.3*e(0.1t)) were not significantly different (likelihood ratio chi(2) = 1.05, df = 2, p = 0.59) from those derived from traditional ages (L-t = 30.7*e(0.009t)). Additionally, FT-NIBS models were capable of predicting otolith weights that were not significantly different from direct measurements (t = 1.75, df = 147, p = 0.08). This study is the first to demonstrate successfully the potential of FT-NIBS to predict daily age and otolith weight in juvenile fishes, as well as the first to manipulate external apertures to optimize signal to noise. These findings support the potential for broad application of FT-NIBS in fisheries biology.

Marine turtles migrate back to their natal region during reproduction, but the precision of this homing behavior and how the precision varies among populations and across biogeographic regions are unclear. We hypothesize that marine turtles nesting on insular landmasses navigate to their rookeries with greater precision than those nesting on continuous coastlines. We analyzed new mitochondrial and microsatellite marker data from hawksbill turtles Eretmochelys imbricata at nesting sites across Antigua and Barbuda, West Indies, to assess the scale of natal homing in the highly insular Leeward Islands. We then used published data from 15 western Atlantic rookeries to examine regional patterns of rookery structure. Mitochondrial control region data showed weak to no partitioning among nesting sites within Antigua and strong partitioning between Antigua and Barbuda, suggesting natal homing at a scale of 50 km. Microsatellite data showed weak to no partitioning between sites, indicating male-mediated gene flow. Regionally, we found stronger population structuring among rookeries of insular landmasses than among those of larger landmasses with continuous coastlines, despite shorter average rookery separation for the former. We also found a positive relationship between a rookery's isolation index (a metric incorporating distances from larger landmasses) and its genetic divergence from proximate rookeries. These findings support our hypothesis, and we caution that insular rookeries that host marine turtles with extreme homing behavior have limited ability to colonize new nesting habitat. The unprecedented rates of development and increasing instability of present-day nesting habitat might therefore pose a greater and increasing threat to insular rookeries.

Mislabeled commercial seafood products are pervasive, worldwide problems that threaten public health, undermine fisheries conservation efforts, and ultimately, lead to consumer financial loss. Although it can be unintentional, deliberately mislabeling of products is a more common trend used to increase profits and/or bypass fishing regulations, both of which are forms of fraud. Unfortunately, oversight, enforcement, and applied research remain insufficient relative to the global scale of the problem. To contribute to a currently small knowledge base on mislabeling rates in European markets, DNA sequence-based barcoding was applied to tissue samples from commercial products and restaurant offerings labeled as Atlantic cod (Gadus morhua) in Spain. Atlantic cod samples (n = 546) were collected from local markets, supermarkets, and restaurants from eight cities (Madrid, Salamanca, Santiago de Compostela, Bilbao, Barcelona, Valencia, Granada, and Seville). DNA barcoding used PCR-based assays of the mitochondrial cytochrome oxidase-I (COI) and 16S rRNA loci. A 6.2% mislabeling rate (34/546 samples) was discovered. There was no evidence of distinct geographic patterns of mislabeling, although tissue samples obtained from restaurants were more likely to be mislabeled than those sampled in markets and supermarkets. Processed forms of product (prepared, salted/smoked) were more likely to be mislabeled than fresh or frozen products. Common ling (Molva molva), haddock (Melanogrammus aeglefinus), saithe (Pollachius virens), and Alaskan pollock (Gadus chalcogrammus) were the most common substitutes, while Nile perch (Lates niloticus) and striped catfish (Pangasianodon hypophthalmus) were the most taxonomically dissimilar to Atlantic cod.

Effective sustainable management of marine fisheries requires that assessed management units (that is, fish stocks) correspond to biological populations. This issue has long been discussed in the context of Atlantic bluefin tuna ( ABFT , Thunnus thynnus ) management, which currently considers two unmixed stocks but does not take into account how individuals born in each of the two main spawning grounds (Gulf of Mexico and Mediterranean Sea) mix in feeding aggregations throughout the Atlantic Ocean. Using thousands of genome‐wide molecular markers obtained from larvae and young of the year collected at the species’ main spawning grounds, we provide what is, to the best of our knowledge, the first direct genetic evidence for “natal homing” in ABFT . This has facilitated the development of an accurate, cost‐effective, and non‐invasive tool for tracing the genetic origin of ABFT that allows for the assignment of catches to their population of origin, which is crucial for ensuring that ABFT management is based on biologically meaningful stock units rather than simply on catch location.

Invasive species threaten native taxa with extirpation and extinction via several biological mechanisms. One such mechanism, hybridization and subsequent introgression of invasive alleles into native genomes is a serious concern, especially for taxa displaying weak reproductive barriers, as is the case for black basses. Black basses introduced outside of their native ranges thus pose elevated threats to endemic congeners, particularly in the southern United States where restricted ranges preclude refuge from introgression. The recently delineated Bartram’s bass (M. sp. cf M. coosae) is endemic to the upper regions of the Savannah River basin, throughout which anthropogenic modification, including impoundment, has been extensive. Non-native Alabama bass (M. henshalli) and smallmouth bass (M. dolomieu) have been introduced into this system on multiple occasions and now threaten Bartram’s bass via introgression. In this study we sampled four reservoirs (Jocassee, Keowee, Hartwell, and Russell) in the upper Savannah River during 2004 and 2010. Results from three codominant nuclear loci and one mitochondrial locus revealed extensive introgression between Alabama and Bartram’s bass. Results show that Alabama bass have replaced Bartram’s bass in lakes Keowee and Russell, where they were first introduced, while the frequencies of hybrids in lakes Jocassee and Hartwell are increasing. Hybridization involving Bartram’s bass with native largemouth bass and introduced smallmouth bass was detected in very low frequencies. Results highlight the importance of continual study over geographic and temporal scales to inform management and conservation of rare fishes threatened with extinction via interspecific hybridization.

Scanning Electron Microscope (SEM) is widely used to investigate surface architecture of a variety of specimens. Observation of most biological specimens under the SEM needs tissue preparation which is fairly well established [1]. Light microscopic observation of sectioned specimens that are paraffin embedded has its limitations. Low-vacuum scanning electron microscopy (SEM) has been used to observe biological samples by avoiding the “charging” impacts even in non-coated samples [2] with the occasional compromise of resolution. In the current study, the conventional protocol of biological sample preparation has been modified by merging a light microscope preparation protocol with that for SEM. This enables evaluation of internal structures of biological specimens by using SEM imaging technique.

The Atlantic bluefin tuna is a highly migratory species emblematic of the challenges associated with shared fisheries management. In an effort to resolve the species’ stock dynamics, a genomewide search for spatially informative single nucleotide polymorphisms (SNPs) was undertaken, by way of sequencing reduced representation libraries. An allele frequency approach to SNP discovery was used, combining the data of 555 larvae and young‐of‐the‐year (LYOY) into pools representing major geographical areas and mapping against a newly assembled genomic reference. From a set of 184,895 candidate loci, 384 were selected for validation using 167 LYOY. A highly discriminatory genotyping panel of 95 SNPs was ultimately developed by selecting loci with the most pronounced differences between western Atlantic and Mediterranean Sea LYOY. The panel was evaluated by genotyping a different set of LYOY (n = 326), and from these, 77.8% and 82.1% were correctly assigned to western Atlantic and Mediterranean Sea origins, respectively. The panel revealed temporally persistent differentiation among LYOY from the western Atlantic and Mediterranean Sea (FST = 0.008, p = .034). The composition of six mixed feeding aggregations in the Atlantic Ocean and Mediterranean Sea was characterized using genotypes from medium (n = 184) and large (n = 48) adults, applying population assignment and mixture analyses. The results provide evidence of persistent population structuring across broad geographic areas and extensive mixing in the Atlantic Ocean, particularly in the mid‐Atlantic Bight and Gulf of St. Lawrence. The genomic reference and genotyping tools presented here constitute novel resources useful for future research and conservation efforts.

In 2007, three rays identified as Rhinoptera brasiliensis based on tooth series counts were captured in the northern Gulf of Mexico, a region far outside their accepted range of the coastal waters of southern Brazil. Genetic analyses confirmed that these individuals were distinct from R. bonasus, the only recognized indigenous rhinopterid in the Gulf of Mexico. Further analyses of over 250 specimens confirmed the widespread occurrence of two species in the northern Gulf of Mexico and revealed that the anomalous individuals related most closely to vouchered specimens of R. brasiliensis from Brazil. Discriminant function analyses of morphological data identified several potential discriminating characters, but the degree of overlap of the measurements and counts between the two species rendered most impractical for identification purposes. However, the shape of the supracranial fontanelle appeared to be consistently reliable in differentiating between the two species. Tooth series counts ( R. bonasus = 5 to 15, R. brasiliensis = usually 7 to 13) were significantly different between the two species but exhibited considerable overlap. This is the first study to verify the occurrence of R. brasiliensis in the northern Gulf of Mexico; however, the close genetic relationships to other rhinopterid species, as well as the morphological similarity of the group as a whole, require additional research.