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Rajiformes

Rajiformes is an order of elasmobranch fishes within the superorder Batoidea, commonly known as skates, characterized by their dorsoventrally flattened bodies, greatly enlarged pectoral fins that fuse with the sides of the head to form a rhomboid or diamond-shaped disc, a slender tail typically bearing two dorsal fins and a small caudal fin, and the absence of an anal fin.^[1] These batoids exhibit undulatory locomotion powered by their pectoral fins and possess ventrally positioned gill slits, with most species being oviparous and laying leathery egg cases.^[1] Rajiformes represent the most speciose group of elasmobranchs, encompassing approximately 305 valid species across four families—Rajidae, Arhynchobatidae, Gurgesiellidae, and Anacanthobatidae—making up nearly half of all batoid diversity.^[2] Skates in the order Rajiformes are predominantly benthic dwellers, inhabiting a wide range of depths from shallow coastal waters to abyssal zones exceeding 3,000 meters, primarily in marine environments but with some species venturing into brackish or freshwater systems.^[3] They are distributed globally across all oceans, with highest diversity in the North Atlantic and Indo-Pacific regions, where species often exhibit restricted ranges contributing to elevated endemism and vulnerability to localized threats.^[4] Morphologically, Rajiformes display a depressed trunk, firm rostral cartilage in most taxa, and defensive features such as thorns or spines along the tail and disc margins, particularly in males during breeding; their diet consists mainly of bottom-dwelling invertebrates and small fishes captured via suction feeding.^[5] The evolutionary history of Rajiformes traces back to the Early Jurassic, approximately 200 million years ago, with the order forming a monophyletic clade within Batoidea that has diversified significantly, especially in deep-water habitats.^[6] Conservation concerns are prominent, as over one-third of skate species face extinction risks due to bycatch in fisheries, habitat degradation, and slow life histories characterized by late maturity and low fecundity; notable examples include large-bodied species like the common skate (Dipturus batis), now critically endangered in parts of its range.^[7] Ongoing taxonomic revisions, informed by molecular phylogenetics, continue to refine family boundaries and species counts, underscoring the order's ecological importance in marine food webs as both predators and prey.^[8]

Taxonomy and Classification

Phylogenetic Position

Rajiformes, commonly known as skates, occupy a prominent position within the class Chondrichthyes, specifically as one of the four primary orders in the superorder Batoidea, alongside Torpediniformes (electric rays), Myliobatiformes (stingrays and allies), and Rhinopristiformes (guitarfishes and wedgefishes).^[9] This placement reflects their monophyletic grouping within elasmobranchs, where Batoidea diverged from shark-like ancestors (Selachimorpha) early in chondrichthyan evolution.^[10] Within Batoidea, Rajiformes is often positioned as the sister group to the remaining batoid orders, supported by both morphological and molecular phylogenies.^[10] Key synapomorphies distinguish Rajiformes from other batoids, including the presence of rostral appendices, medial fusion of the suprascapula to the synarcual, and a curved suprascapula-scapula articulation surface.^[11] Locomotion further highlights these distinctions: Rajiformes employ undulatory motion, propagating multiple waves along their expanded pectoral fins for propulsion, in contrast to the oscillatory flapping seen in Myliobatiformes.^[12] These traits underscore the order's adaptation for benthic lifestyles on soft substrates, differing from the more pelagic or undulatory-oscillatory hybrids in other batoids.^[12] The fossil record of Rajiformes traces back to the Early Jurassic, with the earliest reliable dental remains appearing around 183 million years ago during the Toarcian stage.^[13] This record, though fragmentary and dominated by isolated teeth and vertebrae, reveals transitional forms from shark-like ancestors, such as the sclerorhynchoid rays (e.g., Sclerorhynchus), which exhibit intermediate rostral and fin morphologies bridging primitive elasmobranchs and modern batoids.^[14] These fossils indicate an early diversification within Batoidea, with Rajiformes emerging alongside the initial radiation of flattened-bodied chondrichthyans.^[14] Recent molecular studies reinforce the monophyly of Rajiformes, utilizing mitochondrial DNA markers such as cytochrome c oxidase subunit I (COI) and NADH dehydrogenase subunit 2 (ND2).^[4] For instance, analyses of concatenated mtDNA sequences from over 400 Atlantic skate specimens via maximum likelihood and Bayesian inference methods confirm robust clustering of Rajiformes families (e.g., Rajidae, Arhynchobatidae), supporting their cohesive evolutionary lineage within Batoidea.^[4] Similar mitogenomic phylogenies from complete mitochondrial genomes of multiple skate species further validate this monophyly, highlighting genetic divergence from other batoid orders post-Jurassic.^[15]

Historical and Current Taxonomy

The name Rajiformes derives from the Latin word raja, meaning "ray" (referring to the flattened body shape of these fishes), combined with forma, meaning "shape" or "form".^[16] The order was formally established by Russian ichthyologist Lev Semenovich Berg in 1940 as part of his comprehensive classification of fishes, both recent and fossil.^[17]^[18] Early classifications of rajiform rays were embedded within broader elasmobranch groupings by 19th-century scientists. In their influential Systematische Beschreibung der Plagiostomen (1839–1841), Johannes Müller and Friedrich Gustav Jakob Henle placed rays, including those later assigned to Rajiformes, under the subclass Elasmobranchii, emphasizing their cartilaginous skeleton and gill structure as distinguishing features from bony fishes. This work laid foundational taxonomy for chondrichthyans but did not delineate Rajiformes specifically, treating rays as a subgroup of plagiostome fishes. Subsequent 19th- and early 20th-century systems, such as those by David Starr Jordan, continued to classify skates and rays within Elasmobranchii without a dedicated order, often lumping them with sharks based on morphological similarities like viviparity and dentition. Major taxonomic revisions occurred in the mid-20th century, driven by anatomical studies. A key change came in 1973 when Leonard J.V. Compagno proposed separating electric rays (previously included in Rajiformes) into the distinct order Torpediniformes, based on differences in electric organ morphology, clasper structure, and caudal fin development; this split reduced the scope of Rajiformes to primarily skates and allied forms. Further refinements in the late 20th century, such as those by Compagno in 1999, refined family-level boundaries within Rajiformes using synapomorphies like tail shape and egg case structure. A significant revision in 2016 by Last et al. restricted Rajiformes to the skate families (Rajoidei) and established the order Rhinopristiformes for guitarfishes, wedgefishes, and sawfishes based on integrated morphological and molecular evidence.^[19] In the 2010s, molecular phylogenetic analyses using mitochondrial and nuclear DNA markers began questioning the monophyly of certain families and genera, revealing polyphyletic assemblages; for instance, studies showed the genus Raja as non-monophyletic, with some species clustering closer to other rajid genera, prompting calls for generic revisions.^[20] As of 2025 updates in authoritative databases, Rajiformes remains a valid order encompassing skates, recognized by the World Register of Marine Species (WoRMS) with Berg's 1940 authorship intact.^[17] Ongoing molecular evidence supports the monophyly of Rajiformes within Batoidea, with family boundaries refined through integrated approaches, underscoring the order's distinct evolutionary lineage.

Suborders and Families

The order Rajiformes now encompasses a single suborder, Rajoidei, which includes the skates.^[17] Suborder Rajoidei is distinguished by a diamond-shaped or rounded pectoral disc, a tail often bearing thorns or spines in adults, and primarily oviparous reproduction, laying leathery egg cases known as mermaid's purses, though some deep-water species exhibit viviparity; this suborder contains four families.^[21] The family Rajidae (true skates or hardnose skates), with approximately 165 species in 18 genera such as Raja and Dipturus, is the most diverse and cosmopolitan, emphasizing temperate and polar waters with type genus Raja featuring robust, thorny-tailed forms.^[22]^[2] Arhynchobatidae (softnose skates), comprising about 113 species in 14 genera like Bathyraja, is adapted to deep-sea environments, particularly Antarctic and North Pacific regions, with smoother snouts lacking rostral cartilage.^[23]^[24] Gurgesiellidae (pygmy skates), a small family with 19 species in 3 genera including Gurgesiella, occurs in the western Atlantic and Indo-Pacific and is noted for its diminutive size and reduced dentition.^[25]^[4] Recent taxonomic revisions in the 2020s have elevated Anacanthobatidae (legskates or smooth skates) to distinct family status, with 13 species in 5 genera including Anacanthobatis and Sinobatis, primarily from Indo-Pacific slopes deeper than 200 m, characterized by elongate pelvic fins resembling legs and a smooth, spineless tail.^[26]^[27]

Morphology and Anatomy

Body Structure

Rajiformes, commonly known as skates, exhibit a distinctive dorsoventrally flattened body plan that sets them apart from other chondrichthyans. The pectoral fins are greatly enlarged and fused to the sides of the head and trunk, forming a diamond- or rhomboid-shaped disc that serves as the primary structural element of the body.^[5] This disc varies in width from approximately 25 cm in smaller species, such as the rosette skate (Bathyraja inernaria), to about 1.8 m in larger forms like the big skate (Beringraja binoculata).^[28]^[29] The overall body is depressed and broad, with a short to moderately long snout and a slender tail that tapers posteriorly, lacking the whip-like structure seen in some other batoids.^[5] The endoskeleton of Rajiformes is entirely cartilaginous, a hallmark of chondrichthyans, but adapted for their benthic lifestyle through specific modifications. The vertebral column is reduced in the anterior region, where the first few centra are fused into a rigid synarcual cartilage that supports the disc and enhances structural stability.^[30] The cranium is enlarged and flattened, providing a broad base for the attachment of the pectoral radials, while the rostral cartilage—often stout and calcified in families like Rajidae—extends forward to reinforce the snout in many species.^[5] Calcification patterns in the cartilage, particularly in the radials of the pectoral fins, involve peripheral tesserae that stiffen the skeleton without ossification, allowing flexibility for undulatory motion.^[31] Skin morphology in Rajiformes contributes to both protection and concealment. The dorsal surface is typically covered with dermal denticles or enlarged thorns, often arranged in rows along the midline, snout, and orbits, providing defense against predators.^[32] In contrast, the ventral skin is smooth and lacks prominent denticles, facilitating smoother interaction with the substrate.^[33] Coloration features mottled patterns of browns, grays, and whites on the dorsal side, enabling effective camouflage against sandy or muddy seabeds, while the paler ventral surface aids in countershading.^[28] Morphological variations occur across major groups within Rajiformes. Skates in the family Rajidae possess broader, more rounded or heart-shaped discs with a more pronounced flattening, emphasizing their disc-dominated form.^[5]

Sensory and Locomotory Adaptations

Rajiformes exhibit specialized electroreceptive capabilities through the ampullae of Lorenzini, gelatin-filled pores distributed primarily across the ventral surface of the head and anterior disc. These organs detect bioelectric fields as weak as 5 nV/cm, enabling the detection of prey movements and heartbeats buried in sediment, which is crucial for their benthic foraging strategy.^[34]^[35] Locomotion relies on undulatory waves propagating along the enlarged pectoral fins, producing a rajiform swimming mode that resembles "flying" over the seafloor and contrasts with the axial tail propulsion seen in sharks. This fin-based propulsion provides high maneuverability and efficiency at low speeds, typically around 1-2 km/h (or 1-2 disc lengths per second), with intermittent tail undulations supplementing bursts for acceleration or evasion.^[36]^[37]^[38] Vision is adapted for their dorsoventral body compression, with eyes positioned on the dorsal surface to monitor threats or opportunities from above while the body remains camouflaged against the substrate. Olfaction is similarly enhanced, with large olfactory bulbs processing chemical cues to locate prey in turbid or low-light conditions common to their habitats.^[39]^[40]^[41] In deep-water species, such as certain skates in the genus Bathyraja, spiracles are enlarged to draw oxygenated water over the gills during periods of inactivity on the seafloor, compensating for hypoxic conditions in abyssal environments.^[42]^[43]

Distribution and Habitat

Global Range

Rajiformes exhibit a cosmopolitan distribution, inhabiting all major ocean basins from polar to tropical regions. Species occur across the Atlantic, Pacific, Indian, and Arctic Oceans, as well as the Southern Ocean surrounding Antarctica.^[44] For instance, the Arctic skate (Amblyraja hyperborea) is widely distributed in circumpolar Arctic waters, extending from the Beaufort Sea to the Norwegian Sea and across to the Pacific and Indian Oceans at high latitudes.^[45] In contrast, Eaton's skate (Bathyraja eatonii) is representative of southern polar distributions, commonly found on the Kerguelen Plateau, around the South Orkney and South Shetland Islands, and along the Antarctic Peninsula.^[46] The order predominates in temperate and boreal zones, where cooler waters support a majority of species diversity, particularly in the Northern Hemisphere. Hotspots of occurrence include the Indo-Pacific region, encompassing diverse shelf and slope habitats from the Arabian Sea to the western Pacific, and the North Atlantic, where multiple genera thrive along continental margins.^[47] This latitudinal bias reflects adaptations to benthic lifestyles in mid- to high-latitude environments, though some taxa extend into subtropical areas.^[44] Bathymetrically, Rajiformes span a wide range, from shallow coastal shelves at depths of 0–200 m to abyssal plains exceeding 3,000 m, with many species favoring continental slopes between 200–1,000 m. Deep-water forms, such as certain rajids, reach these extreme depths in polar and temperate basins, facilitated by their flattened body morphology suited to demersal existence.^[48] Endemism patterns underscore regional specialization, with elevated diversity and unique assemblages in semi-enclosed or isolated basins. The Mediterranean Sea hosts several endemic skates, contributing to its status as a hotspot for restricted-range species amid high overall elasmobranch richness.^[49] Similarly, the Southwest Atlantic features notable endemism, with approximately 32 skate species, many confined to shelf and slope habitats from southern Brazil to Argentina, highlighting localized evolutionary divergence.^[50]

Environmental Preferences

Rajiformes species predominantly inhabit benthic environments characterized by soft-bottom substrates such as mud and sand, which facilitate burial for camouflage and ambush predation.^[51] These substrates allow skates and rays to blend into the seafloor, reducing visibility to predators and prey, with undulations of their pectoral fins stirring sediment to enhance concealment.^[52] While most prefer these unconsolidated sediments across continental shelves and slopes, certain species, such as those in deeper waters, occupy rocky or cobble reefs where harder substrates support alternative foraging strategies.^[52] Temperature tolerances among Rajiformes vary by habitat and taxon, with the majority of temperate and polar species thriving in cool waters ranging from 0°C to 20°C.^[53] For instance, deep-water skates like Bathyraja parmifera are commonly found in near-bottom temperatures of 0–3°C.^[53] Some subtropical representatives, such as the clearnose skate (Rostroraja eglanteria) in the family Rajidae, tolerate temperatures up to 27°C in shallow coastal zones.^[54] Recent climate studies from the 2020s highlight their sensitivity to warming, with experimental exposures showing physiological stress in elasmobranchs, including reduced metabolic efficiency and altered distribution patterns under projected ocean temperature increases.^[55] Most Rajiformes are strictly marine, adapted to full oceanic salinity levels around 35 ppt, though some rajids exhibit euryhaline capabilities, tolerating brackish estuarine conditions down to 12 ppt.^[54] Species like the clearnose skate (Rostroraja eglanteria) demonstrate partial euryhalinity, enabling occasional incursions into estuaries for foraging or refuge.^[56] Regarding oxygen, Rajiformes generally avoid hypoxic zones with dissolved oxygen below 2 mg/L, as these conditions impair gill function and metabolic rates, prompting behavioral relocation to better-oxygenated areas.^[57] Migratory behaviors in Rajiformes are closely linked to environmental gradients, particularly seasonal shifts in temperature and substrate availability for spawning.^[58] Many skates undertake annual shelf migrations, moving to shallower, warmer coastal waters in spring and summer to access optimal spawning grounds on soft sediments, before retreating to deeper, cooler habitats in winter.^[59] For example, thornback rays (Raja clavata) exhibit clear cycles of inshore migration for reproduction between March and August, driven by temperature cues exceeding 10°C.^[58] These movements ensure alignment with peak productivity periods while avoiding extremes in salinity or oxygen depletion.^[60]

Diversity

Species Diversity

Rajiformes, encompassing skates and related batoids, represent the most speciose order within Batoidea, with approximately 300 valid species recognized worldwide as of 2025.^[1] This diversity surpasses that of other batoid orders, driven by adaptive radiations in varied marine environments. Since 2020, at least 10 new species have been described, primarily within the family Rajidae, including deep-water forms such as Bathyraja nansei from the Okinawa Trough and Leucoraja longirostris from the Southwestern Indian Ocean, highlighting ongoing taxonomic discoveries facilitated by advanced molecular and morphological analyses.^[61]^[62] Patterns of species richness in Rajiformes reveal hotspots concentrated in the Indo-West Pacific, where approximately 40% of known species occur, reflecting the region's role as a center of marine biodiversity.^[1] High endemism is evident in isolated habitats, such as seamounts and polar regions; for instance, several Bathyraja species are restricted to Antarctic seamounts and Arctic shelves, comprising up to 20% of local batoid assemblages in these areas.^[63] The family Rajidae accounts for about 50% of total Rajiformes diversity, largely due to adaptive speciation in cold-water environments that promote morphological and ecological divergence. Evolutionary trends in Rajiformes trace a major radiation during the Miocene, coinciding with global cooling and tectonic changes that expanded continental shelf habitats suitable for benthic lifestyles.^[64] This period facilitated parallel diversifications across suborders, leading to the current high species counts, particularly in temperate and polar zones where Rajidae thrived through niche specialization.^[6] Conservation assessments underscore threats to this diversity, with approximately 30% of Rajiformes species classified as Data Deficient by the IUCN due to limited distributional and population data, complicating risk evaluations.^[65] As of 2021, approximately 33% of assessed elasmobranch species, including many skates, are classified as threatened (Critically Endangered, Endangered, or Vulnerable) by the IUCN, with ongoing increases driven by bycatch in deep-sea fisheries and habitat degradation in biodiversity hotspots.^[66]

Major Taxonomic Groups

The Rajidae, commonly known as skates, represent one of the most diverse and ecologically significant families within Rajiformes, comprising over 200 species characterized by their rhomboidal to heart-shaped pectoral discs, thorned or denticled dorsal surfaces, and slender tails often bearing thorns, particularly in males. These oviparous fishes, which lay leathery egg cases, dominate cold-temperate to polar waters on continental shelves and slopes, with habitats ranging from intertidal zones to depths exceeding 4,000 meters on soft sandy or muddy bottoms. Unique traits include a stout rostral cartilage supporting the snout, alar thorns on the pectoral fins of mature males, and the absence of a venomous sting, distinguishing them from more ray-like relatives; representative species include the common skate (Dipturus batis), a large Atlantic form reaching up to 285 cm in disc width, now assessed as critically endangered due to overfishing and habitat degradation.^[5]^[67] The Arhynchobatidae, or softnose skates, are a diverse family with around 104 species in 13 genera, featuring softer snouts without prominent rostral cartilage, angular to rounded discs, and adaptations for deep-sea life, including reduced ornamentation and elongated tails; they are primarily benthic in temperate to polar waters, from continental slopes to abyssal depths exceeding 2,000 meters, over soft substrates, and are mostly ovoviviparous. High endemism characterizes this group, with many species restricted to seamounts or oceanic islands; examples include Bathyraja irrasa from the North Pacific, vulnerable due to limited range and bycatch.^[68] The Gurgesiellidae, known as pygmy skates, comprise about 15 small-bodied species (typically under 40 cm total length) in three genera, with rounded discs, reduced rostral structures, and smooth skins lacking prominent thorns; these oviparous skates inhabit subtropical to tropical shelf and slope waters up to 1,000 meters deep, primarily in the southwestern Atlantic and Indo-West Pacific, over muddy or sandy bottoms. They feed on small invertebrates and are often data deficient due to rarity in collections; a representative is Gurgesiella atlantica from the western Atlantic, assessed as least concern but with sparse data.^[25]^[69] The Anacanthobatidae, or legskates, possess broad, rounded discs, naked skins without prominent thorns, and leg-like anterior pelvic fin lobes that facilitate walking on the seafloor, with no dorsal fins and a slender tail; limited to about 10 species in tropical to temperate waters at depths of 150-1,600 meters over soft substrates, they represent an adaptation to abyssal environments. Ovoviviparity and small size (up to 66 cm total length) are typical, as seen in Anacanthobatis melanosoma, which occurs in the Indo-Pacific slope habitats.^[5]^[70] Morphological gradients across these families reflect ecological specializations, from the disc-dominant, benthic ambush forms of Rajidae in cold, deep settings to the reduced, leg-like structures of Anacanthobatidae in abyssal tropics, with Arhynchobatidae and Gurgesiellidae showing intermediate adaptations for slope and shelf environments.^[5]

Biology and Ecology

Reproduction and Development

Rajiformes exhibit oviparity, laying eggs encased in leathery capsules known as mermaid's purses.^[20] These capsules, typically containing one embryo per case in most species, protect the developing embryo and are deposited on the seafloor in benthic habitats; however, certain species like the big skate (Beringraja binoculata) can have up to eight embryos per capsule, with two being the most common.^[20] Mating in Rajiformes involves internal fertilization facilitated by male claspers, paired structures that transfer sperm during courtship, which may include biting or pectoral fin displays in skates.^[71] Breeding is often seasonal, with peaks in spring and summer for temperate species; for example, the thornback ray (Raja clavata) spawns primarily from May to January, peaking in August.^[72] Fecundity varies but remains relatively low, with oviparous skates producing 20–136 eggs per season across multiple batches—for instance, R. clavata lays about 136 eggs annually—contributing to their vulnerability due to slow population recovery.^[72] Embryonic development in oviparous Rajiformes proceeds directly to hatching without a free-living larval stage, relying on yolk-sac nutrition absorbed over the incubation period.^[73] Incubation times range from 2 to 12 months depending on species and temperature; the bignose fanskate (Sympterygia acuta) hatches after 97 days at 11–21.7°C, while the flapper skate (Dipturus intermedius) requires about 534 days at around 10.9°C.^[73]^[74] Sexual maturity is reached at 3–15 years, varying by species and size; for example, the little skate (Leucoraja erinacea) attains 50% maturity at about 9.5 years for females, while some smaller species mature in 3–4 years.^[75]^[76]

Feeding and Behavior

Rajiformes, comprising skates, exhibit feeding strategies adapted to their benthic lifestyles, primarily targeting small to medium-sized prey in marine sediments. Their diet consists mainly of benthic invertebrates, including crustaceans (such as shrimps, crabs, and amphipods), mollusks, polychaete worms, and cephalopods, supplemented by small teleost fishes. Skates in the family Rajidae often use a specialized feeding mechanism involving hyostylic jaw protrusion, where the upper jaw extends forward to create suction for capturing buried prey like worms and crustaceans directly from the substrate.^[77]^[78] Foraging behaviors in Rajiformes emphasize energy-efficient predation suited to their ectothermic metabolism. Many species, particularly skates and stingrays, adopt ambush tactics by burying themselves in soft sediments, using their dorsoventrally flattened bodies to remain concealed while detecting prey via electroreception and mechanosensory cues. Nocturnal and crepuscular activity predominates, with heightened foraging during low-light periods to reduce predation risk and exploit prey availability; for instance, deep-water skates show increased consumption of crustaceans and fish at night. Deep-sea forms, such as certain Bathyraja species, also engage in opportunistic scavenging, feeding on carrion that sinks to the seafloor, which aligns with their low metabolic rates and infrequent feeding cycles.^[79]^[78]^[80] Social behaviors among Rajiformes are generally subdued, reflecting their solitary or loosely affiliative lifestyles. Adults are typically solitary foragers, though juveniles may form small schools or aggregations in nursery habitats for protection, potentially facilitating shared foraging opportunities in resource-rich areas. Agonistic interactions are minimal in core groups like Rajidae, lacking prominent displays such as electric discharges seen in related torpediniform rays; instead, occasional tail lashes may occur during territorial disputes over feeding grounds. These patterns support efficient energy budgets, as their low-metabolism ectothermy allows prolonged fasting between meals, with daily rhythms centered on crepuscular peaks to optimize prey capture while conserving resources.^[81]^[82]^[79]

Conservation and Human Interactions

Threats and Status

Rajiformes, comprising skates and related taxa, face severe threats primarily from overfishing, with bycatch in demersal trawl fisheries accounting for the majority of mortality, estimated at around 80% for discarded individuals due to high at-vessel and post-release death rates from stress and injury.^[83] Targeted fisheries exacerbate declines, particularly for skate wings used in food markets, leading to population reductions of up to 90% in heavily exploited regions. Habitat degradation from bottom trawling further compounds these pressures by disrupting benthic ecosystems essential for foraging and reproduction. According to the latest IUCN Red List assessments as of 2025, approximately 37% of chondrichthyan species, including those in Rajiformes, are classified as threatened (Vulnerable, Endangered, or Critically Endangered), with batoids like skates showing a heightened risk at 36% threatened due to their vulnerability to fishing.^[84]^[65] Iconic species such as the common skate (Dipturus batis) are Critically Endangered, reflecting drastic declines from historical overexploitation. Around 13% of species remain Data Deficient, largely owing to challenges in monitoring deep-sea populations and limited survey data in remote habitats.^[65] These low reproductive rates, characterized by slow growth and late maturity, amplify susceptibility to even moderate fishing pressure. Climate change poses additional cumulative threats, driving poleward range shifts in response to warming waters that alter prey distribution and habitat suitability for temperate skates. Ocean acidification impairs embryonic development in egg-laying species by weakening egg cases and reducing hatchling viability, particularly when combined with elevated temperatures.^[85] These effects are pronounced in biodiversity hotspots, where synergistic stressors intensify extinction risks for already depleted populations.^[86] Regional variations highlight uneven threats, with severe overexploitation in the North Atlantic leading to local extinctions of large-bodied skates from intensive trawl and longline fisheries.^[87] In the Indo-Pacific, species often exhibit restricted ranges contributing to elevated endemism and vulnerability to localized threats.^[4]

Fisheries and Management

Rajiformes species, particularly skates, are exploited in global fisheries primarily for their meat, which serves as a protein source in various regions. Annual global landings of skates and rays have been reported at approximately 450,000 metric tons in recent FAO data as of 2021, though specific figures for Rajiformes alone are lower and dominated by European skate fisheries (e.g., Raja and Dipturus species) contributing around 20,000-30,000 tons annually.^[88]^[89] Management strategies for Rajiformes fisheries include total allowable catches (TACs) and quotas established by the European Union since 2010, such as limits on Dipturus species in the North Sea and Celtic Sea to prevent overfishing of vulnerable stocks, with exemptions for certain protected skates like the common skate (Dipturus batis).^[90] Additionally, marine protected areas (MPAs) in biodiversity hotspots, such as the Galapagos Marine Reserve, prohibit targeted fishing of rays and skates, providing refuge for regional species and supporting population stability through no-take zones.^[91] Monitoring techniques in Rajiformes fisheries rely on genetic barcoding of the mitochondrial COI gene to accurately identify species in mixed catches and processed products, as demonstrated in retail surveys across the UK and Ireland where mislabeling was prevalent. Acoustic tagging has also been employed to study movement patterns, with thornback ray (Raja clavata) individuals tracked in Portuguese MPAs to inform spatial management and reveal seasonal migrations over several kilometers. These methods enhance enforcement and stock assessments by distinguishing cryptic species and quantifying bycatch impacts.^[92]^[93]^[94] The thornback ray (Raja clavata) has shown signs of partial recovery in the Irish Sea, potentially aided by interim conservation measures and the planned inshore trawling ban, with full prohibition for vessels over 18 meters within 6 nautical miles set for October 2026, as evidenced by improved survey abundances in protected areas. However, challenges persist in international waters, where unregulated high-seas fisheries lead to continued declines in deep-water skates, with inadequate reporting and enforcement exacerbating overexploitation in areas like the Falkland Islands' exclusive economic zone.^[95]^[96]^[97]^[98]

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[18]
Rajiformes - GBIF
Berg, L.S. (1940). Classification of fishes, both recent and fossil. <em>Trav. Inst. Zool. Acad. Sci.</em> 5(2):517. Compagno, Leonard J. V. / Hamlett, William ...
[19]
The secret of the mermaid's purse: Phylogenetic affinities ... - NIH
Rajid skates are oviparous, and lay egg capsules with a single embryo. However, two species exhibit a derived form of egg laying, with multiple embryos per egg ...
[20]
Eschmeyer's Catalog of Fishes - Genera/Species by Family/Subfamily
Oct 10, 2025 · Various authors cite the number of species in a particular family or subfamily, especially in family revisions. ... Rajidae, 34, 18, 2, 286, 161 ...
[21]
FAMILY Details for Rajidae - Skates - FishBase
Family Rajidae - Skates ; Order, : Rajiformes ; Class, : Elasmobranchii ; No. in FishBase, : Genera : 18 | Species : 165 Eschmeyer's Catalog of Fishes ; Environment ...
[22]
A taxonomic revision of Northeast Pacific softnose skates (Rajiformes
May 31, 2022 · Softnose skates (Rajiformes: Arhynchobatidae: Bathyraja Ishiyama) are the most diverse skate genus, with 54 species, and are readily ...Missing: sources | Show results with:sources
[23]
https://www.fishbase.se/summary/FamilySummary.php?ID=685
[24]
[PDF] Legskates : family Anacanthobatidae - Horizon IRD
The family includes 13 species in 5 genera: Anacanthobatis, Indobatis, Schroederobatis, Sinobatis and Springeria. Some of these species were only recently ...Missing: elevation taxonomy
[25]
https://www.fishbase.se/summary/FamilySummary.php?ID=715
[26]
[PDF] Proposal for amendment of Appendix I or II for CITES CoP18
May 24, 2022 · The family Rhinobatidae contains 37 species of guitarfishes (listed in Annex 1 of this proposal); 35 of the 37 species are in decline, 23 of the ...Missing: count | Show results with:count
[27]
https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers21-02/010072281.pdf
[28]
Wedgefish - CITES Sharks and Rays
All 10 species of wedgefish (Rhinidae) for listing on CITES Appendix II. Wedgefish species are the third most threatened family of chondrichthyan fishes ...Missing: count | Show results with:count
[29]
Big Skate – Discover Fishes - Florida Museum of Natural History
Feb 6, 2025 · Usually a mottled reddish-brown to dark grey on top, and scattered with small pale spots and larger dark blotches, they also have dark 'eye ...
[30]
The Synarcual Cartilage of Batoids With Emphasis ... - ResearchGate
Aug 6, 2025 · However, other synapomorphies are identified which suggest that additional factors must be sought to fully understand the origin of Mammalia.Missing: distinguishing | Show results with:distinguishing
[31]
Morphology of joints and patterns of cartilage calcification in the ...
Jan 17, 2022 · Radials are long and narrow cartilage elements aligned in straight lines in the wings of a flattened biconvex shape (perpendicular to the wing ...
[32]
Rajiformes: Skates - ReefQuest Centre for Shark Research
257 to 275 species ; Rajoids lead unobtrusive, secretive lives, mostly hidden away in deep waters beyond human commerce and concern. Some of the ...
[33]
Order Summary for Rajiformes - FishBase
Class etymology. : Greek eulanein, elasmos = metal beaten out + Greek brangchia = gills. Ref. 45335. Order etymology. : Latin, raja = ray + Latin, forma ...Missing: Blainville 1816
[34]
Common Guitarfish - NOAA Fisheries
Feb 21, 2017 · All guitarfishes have a moderately depressed, elongated, shark-like body form, two equal, well-developed, and well-separated dorsal fins, and an ...
[35]
Little Skate – Discover Fishes - Florida Museum of Natural History
Feb 6, 2025 · The little skate possesses an electrosensory known as ampullae of Lorenzini. This organ is found on the head and consists of many tiny gel ...
[36]
Molecular basis of ancestral vertebrate electroreception - PMC
Elasmobranch fishes, including sharks, rays, and skates, use specialized electrosensory organs called Ampullae of Lorenzini to detect extremely small changes in ...
[37]
Rajiform locomotion: Three-dimensional kinematics of the pectoral ...
Aug 6, 2025 · Pectoral fin locomotion was supplemented by intermittent caudal fin undulation as swimming speed increased. At the pectoralcaudal gait ...
[38]
Batoid Fishes: Inspiration for the Next Generation of Underwater ...
The focus of this paper is to present the growing body of work being done to under- stand and quantify the swimming per- formance of batoid fishes (i.e., skates ...
[39]
Fin systems comparative anatomy in model Batoidea Raja asterias ...
May 1, 2023 · The swimming styles of this super‐order have been distinguished in "Mobuliform", characterized by flapping of the pectoral fins (in pelagic ...
[40]
[PDF] VISUAL ADAPTATIONS IN SHARKS, SKATES AND RAYS
seeking prey items (Robins and Ray 1986). The dorsally positioned eyes are periscopic enabling them to protrude above the substrate when the ray is buried.
[41]
Sniffing out Stingray Noses: The Functional Morphology of Batoid ...
Olfaction is important for long-distance tracking and navigation, predator and prey recognition, and conspecific signaling. However, the mechanisms by which ...
[42]
Sniffing out Stingray Noses: The Functional Morphology of Batoid ...
Oct 21, 2022 · Olfaction is important for long-distance tracking and navigation, predator and prey recognition, and conspecific signaling.
[43]
[PDF] Anatomy Of A Stingray
Nov 3, 2023 · Stingrays have specialized sensory organs called ampullae of Lorenzini around their heads, which detect electrical signals produced by prey.
[44]
(PDF) The Fishery Biology of Two Deep-Water Skates, Bathyraja ...
Nov 14, 2024 · Chile is a biodiverse region for deep-water skates (Rajiformes), with 36 species documented in national waters, of which 73% correspond to deep- ...
[45]
In situ observations of deep-living skates in the eastern North Pacific
Although they are morphologically conservative, skates have an extremely broad, cosmopolitan distribution, occurring from high latitude polar waters to low ...
[46]
Amblyraja hyperborea, Arctic skate - FishBase
The Arctic skate is a marine, deep-water skate found in Arctic, Indian, Pacific and Atlantic oceans, with a grey-brown body and dark blotches. It lives in cold ...
[47]
Bathyraja eatonii | Shark-References
Distribution Southern Ocean: common on the Kerguelen Plateau, around South Orkney and South Shetland islands. In the Antarctic Peninsula, it occurs in the ...
[48]
Functional diversity of sharks and rays is highly vulnerable ... - Nature
Nov 24, 2023 · Overlapping hotspots were spread out mostly across the Indo-Pacific (northern Australia, much of the shelf from India to Southern Japan and ...
[49]
Morphological Characters of the Thickbody Skate Amblyraja frerichsi ...
Besides this geographical extension, the bathymetric distributional range is also extended, inhabiting between 800 and 2,200 m depth. It is urgent to focus ...<|separator|>
[50]
Uncommon biological patterns of a little known endemic ...
Rare and poorly studied species, like the endemic skates of the Mediterranean Sea, are considered prone to high rates of extinction and threat because of ...
[51]
DNA Barcoding Southwestern Atlantic Skates: A 20-Year Effort in ...
Skates (Chondrichthyes, Rajiformes) constitute a monophyletic and cosmopolitan group of cartilaginous fishes, with representatives in all oceans. They inhabit ...
[52]
[PDF] Sharks, Skates and Rays Species Status Assessments
The most recent IUCN assessment in 2019 lists Barndoor skates as least concern in Northeast US (Kulka et al., 2020). II. Abundance and Distribution Trends i.
[53]
[PDF] Deep–sea Cartilaginous Fishes of the Indian Ocean. Volume 2 ...
Jun 4, 2015 · orders, Torpediniformes, Pristiformes, Rajiformes, and ... lobes well developed with deep incised separation from posterior lobes. Tail ...
[54]
(PDF) Distribution and some biological features of skate Bathyraja ...
Aug 7, 2025 · The temperature range of the near-bottom layer of water at which the species was encountered was 0-3.0°С. High values of relative abundance ...
[55]
Tropical rays are intrinsically more sensitive to overfishing than the ...
We found that warm, shallow-water rays were more intrinsically sensitive to exploitation (lower r max ) than cold, deep-water skates (higher r max ).
[56]
Elasmobranch Responses to Experimental Warming, Acidification ...
We searched the literature for peer-reviewed studies featuring a sustained (>24 h) and controlled exposure of elasmobranch species to warming, acidification, ...
[57]
Some euryhalinity may be more common than expected in marine ...
... Rhinobatidae) ... brevirostris can be considered a partially euryhaline species, a marine species that could potentially use estuarine brackish areas.
[58]
Some euryhalinity may be more common than expected in marine ...
May 7, 2013 · Some euryhalinity may be more common than expected in marine elasmobranchs: the example of the South American skate Zapteryx brevirostris ( ...
[59]
The vulnerability of sharks, skates, and rays to ocean deoxygenation ...
Jun 9, 2024 · Spatial avoidance is likely a common response of mobile aquatic animals exposed to hypoxia (Jensen et al., 1993). However, hypoxia can inhibit ...
[60]
Seasonal migration of thornback rays and implications for closure ...
Jun 23, 2006 · However, 77% of rays moved outside the estuary over winter, with seasonal migration into the Thames to spawn between March and August.
[61]
Raja clavata, Thornback ray : fisheries, gamefish - FishBase
Undertakes migrations with mean distances of 54-117 km per month; shows a clear annual migration cycle (Ref. 89017, 89018), moves from deeper offshore ...
[62]
[PDF] NYSDEC SWAP SGCN Sharks Skates Rays - NY.gov
Skates migrate seasonally in response to temperature changes, occurring in shallower water in the spring and autumn (Bigelow and Schroeder 1953).Missing: Rajiformes oxygen
[63]
Bathyraja nansei, a new deep‑water softnose skate (Rajiformes
Aug 7, 2025 · The number of valid skate species has increased exponentially, with more species ... diversity and recognized 4476 valid species, which ...
[64]
Marine Biologists Discover Remarkable New Species of Deep ...
Oct 15, 2024 · Named Leucoraja longirostris (common name is the brown longnose skate), it is apparently endemic to the Madagascar Ridge at Walters Shoals.
[65]
[PDF] Biophysical and ecological overview of the Tuzo Wilson Seamount ...
Note: All are in the Pacific Region, there are no known seamounts in the Atlantic or Arctic Regions. ... (Rajiformes: Arhynchobatidae: Bathyraja Ishiyama).
[66]
Skate (fish) - Wikipedia
Alternatively, the name "skate" is used to refer to the entire order of Rajiformes (families Anacanthobatidae, Arhynchobatidae, Gurgesiellidae and Rajidae).
[67]
Rapid Miocene–Pliocene dispersal and evolution of Mediterranean ...
Nov 18, 2004 · Rajidae (colloquially known as skates and rays) experienced multiple and parallel adaptive radiations allowing high species diversity and ...
[68]
Overfishing drives over one-third of all sharks and rays toward a ...
Nov 8, 2021 · Now, 391 (32.6%) species are threatened with extinction. When this percentage of threat is applied to Data Deficient species, more than one- ...
[69]
Tracking the rising extinction risk of sharks and rays in the Northeast ...
Jul 28, 2021 · We incorporate predicted categorisations for Data Deficient species from our previously published research. The percentage of threatened species ...
[70]
https://www.fishbase.se/summary/FamilySummary.php?ID=260
[71]
[PDF] Order RHINOBATIFORMES
Maximum total length at least 82 cm; a dwarf species, with term fetuses between 21 and 24 cm, an adolescent male 65 cm, an adolescent female about 69 cm, and ...<|separator|>
[72]
FAMILY Details for Rhinobatidae - Guitarfishes - FishBase
Nov 29, 2012 · Family Rhinobatidae - Guitarfishes ; Order, : Rhinopristiformes ; Class, : Elasmobranchii ; No. in FishBase, : Genera : 4 | Species : 40 ...Missing: count | Show results with:count
[73]
Rhinobatos - Common guitarfish - FishBase
Inhabits sandy and muddy bottoms, from the intertidal zone to about 100 m. Sometimes near rocky reefs (Ref. 12951). Slow swimming over bottom or partially ...
[74]
https://onlinelibrary.wiley.com/doi/10.1111/jfb.14816
[75]
[PDF] Reproductive biology of the spotted guitarfish Rhinobatos punctifer ...
Jan 9, 2024 · R. punctifer is an aplacental viviparous species, with each female having two ovaries and two uteri, both functional. Ripe oocytes in the ...
[76]
[PDF] Mating behavior, egg deposition, incubation period, and hatching in ...
We have found that but one mating, and sperm transfer by a single clasper, is necessary to provide sperm that remain viable for at least three months while ...Missing: Rajiformes | Show results with:Rajiformes
[77]
Maturation, fecundity, and spawning strategy of the thornback ray ...
Aug 10, 2025 · During the spawning season, a total of four batch episodes occur indicating that the total fecundity was approximately 136 eggs per female.
[78]
Rajiformes): Sympterygia acuta as the first case study in the family ...
The family Arhynchobatidae currently comprises 108 valid species and ranks second in species number behind Rajidae—the most ancestral skate family (Naylor et al ...
[79]
First confirmed complete incubation of a flapper skate (Dipturus ...
Jun 2, 2021 · Hatching occurred after 534 days, suggesting that flapper skate eggs take c. 5700 growing degree-days to incubate to hatching. The egg's ...
[80]
Size and age estimates at sexual maturity for the little skate ...
Dec 3, 2009 · Maturity ogives suggest that 50% maturity in females occurs at age 9·5 years and 480 mm total length (LT), whereas 50% maturity in males occurs ...
[81]
Age, growth and maturity of an endemic valuable resource, the Rio ...
Feb 5, 2024 · Rioraja agassizii is a vulnerable species endemic to the Southwest Atlantic. It is caught by trawl fisheries throughout its range.
[82]
A Comparative Analysis of Feeding and Trophic Level Ecology in ...
Aug 1, 2013 · The Myliobatoidei is second largest suborder within the Rajiformes and comprises a morphologically diverse group of seven families, three ...Missing: diversity | Show results with:diversity
[83]
[PDF] The Diets and Feeding Habits of Some Deep-Water Benthic Skates ...
The pur- pose of this paper is to describe the diets of 7 species of deep-benthic skates of the genus Bathyraja that in- habit the Pacific waters off the North ...
[84]
(PDF) Anatomy and functional morphology of the feeding apparatus ...
The ray captures its prey by protruding its jaws beneath the substrate and generating subambient buccal pressure to suck worms into its mouth. Initiation of ...
[85]
[PDF] Nocturnal and crepuscular behavior in elasmobranchs: a review of ...
ABSTRACT.—It is commonly assumed that elasmobranchs. (sharks, skates, and rays) are most active during dark periods. (dawn, dusk, night).
[86]
(PDF) The Diets and Feeding Habits of Some Deep-Water Benthic ...
Aug 6, 2025 · Benthophagic skates (sandpaper skate, Okhotsk skate, and probably whitebrow skate) consumed mainly amphipods and worms. The consumption of worms ...
[87]
None
### Summary of Social Behavior, Grouping, and Agonistic Displays in Skates and Rays (Rajiformes, Batoidea)
[88]
Diel Rhythm and Thermal Independence of Metabolic Rate in a ...
Jul 13, 2022 · Of the aquatic ectotherms, the elasmobranchs (i.e. sharks, rays, and skates) host an array of species that are crepuscular or nocturnal with ...
[89]
[PDF] Discard survival estimates of commercially caught skates of the ...
In the North East Atlantic, rays and skates are caught as bycatch in otter- and beam-trawl fisheries ... ray caught by beam trawlers are high (~80%) (Ellis et al.
[90]
Ocean acidification exacerbates the impacts of global warming on ...
Increased warming and acidification reduce body condition of newly-hatched skates. •. Body condition correlates with the latency of hatchlings to begin feeding.
[91]
Sharks, Rays, and Climate Change: Impacts on Habitat, Prey ...
Jul 12, 2023 · Warming ocean temperatures and more intense storms caused by climate change are impacting prey availability and habitat quality for migratory sharks and rays.
[92]
Quarter of northeast Atlantic sharks and rays threatened with extinction
Nov 10, 2008 · Overexploitation, from targeted fisheries as well as incidental take (or “bycatch”) is the primary cause of declines in Northeast Atlantic ...
[93]
[PDF] bowmouth guitarfish - Rhina ancylostoma - CITES
Jan 11, 2021 · Magnitude of illegal trade ... severely depleted in significant areas of the Indo-West Pacific, including India and Southeast Asia (Stobutzki et ...<|control11|><|separator|>
[94]
[PDF] Western Central Atlantic Fishery Commission Region
FAO (2020–2023). Saint Lucia. 87. <40. FAO (2018b). Saint Vincent and the ... species: Rajiformes – rays, stingrays, mantas nei. species code: –. Cuba. 1 343.
[95]
Council Regulation (EU) No 23/2010 of 14 ... - Legislation.gov.uk
All catch limits set out in this Annex shall be considered as quotas for the purposes of Article 5 of this Regulation and shall therefore be subject to the ...
[96]
[PDF] CoP20 Prop. 33 – p. 1 - CITES
1.4 Species: Rhynchobatus australiae Whitley, 1939; Rhynchobatus djiddensis (Forsskål, 1775);. Rhynchobatus cooki Last, Kyne & Compagno, 2016; Rhynchobatus ...
[97]
(PDF) DNA barcoding unveils skate (Chondrichthyes - ResearchGate
Aug 10, 2025 · For the first time, DNA barcoding (of the mitochondrial COI gene) was applied to samples of skate wings from retail outlets across the British ...
[98]
Identification of Rays through DNA Barcoding - PubMed Central - NIH
Jun 11, 2012 · Here, we report an application of DNA-barcoding to confirm the identification of rays as part of ecological studies at Ningaloo Reef. The ...
[99]
Seasonal movement dynamics of the commercially important ...
Aug 1, 2024 · Diel vertical migrations or nocturnal ascent has been described for thornback rays and other skates in the genus Raja (Humphries et al., 2017; ...
[100]
Ireland reinstitutes inshore trawling ban | SeafoodSource
Aug 6, 2025 · In January 2020, Ireland began enforcing a ban on trawlers over 18 meters in length operating inside 6 nautical miles of the country's coast.
[101]
Thornback ray - Rating ID: 854 | Good Fish Guide
The Thornback ray has a rating of 3: OK, meaning it is not overfished, but lacks a management plan and has moderate bycatch.Missing: bans | Show results with:bans
[102]
Opportunistic Survey Analyses Reveal a Recent Decline of Skate ...
Dec 30, 2022 · Data were combined from surveys in 2013, 2018, 2019 and 2021 to examine biomass changes of the skate (Rajiformes) stock in waters around the Falkland Islands.