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Rajiformes
Temporal range: Pliensbachian–Recent [1]
Little skate (Leucoraja erinacea)
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Clade: Euselachii
Subclass: Elasmobranchii
Division: Batomorphi
Order: Rajiformes
L. S. Berg, 1940

Rajiformes /ˈrædʒɪfɔːrmiːz/ is one of the four orders in the clade Batomorphi, often referred to as the superorder Batoidea, flattened cartilaginous fishes related to sharks.[2] Rajiforms are distinguished by the presence of greatly enlarged pectoral fins, which reach as far forward as the sides of the head, with a generally flattened body. The undulatory pectoral fin motion diagnostic to this taxon is known as rajiform locomotion. The eyes and spiracles are located on the upper surface of the head and the gill slits are on the underside of the body. Most species give birth to live young, although some lay eggs enclosed in a horny capsule ("mermaid's purse").[citation needed]

Characteristics

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Rajoids typically have a dorsoventrally flattened body. The snout is slender and pointed and the wide mouth, often covered with a fleshy nasal flap, is on the underside of the head. The eyes and well-developed spiracles are located on the top of the head. In most species, the spiracles are large and are the main means of drawing water in for respiration. There is no nictitating membrane and the cornea is continuous, with the skin surrounding the eyes. The gill slits are on the ventral surface just behind the head.[citation needed] The front few vertebrae are fused into a synarcual and this either articulates with the bones of the well-developed pectoral girdle or is fused to them, the suprascapulae uniting above the vertebral column.[3] Most species have enlarged, thornlike dermal denticles on their skin, often with a row of large denticles along the spine.[4]

The pectoral fins are large, but not clearly demarcated from the body, and together with the body are known as the disc. They start from the side of the head in front of the gill openings and end at the caudal peduncle. There are up to two dorsal fins but no anal fin. A slender tail is clearly demarcated from the disc. The caudal fin varies in size between species and the rays have a whip-like tail with no caudal fin.[4]

Distribution

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Species of the order Rajiformes are found throughout the world's oceans, from Arctic to Antarctic waters, and from shallow coastal shelves to open seas and abyssal regions. A few are found in rivers and some in estuaries, but most are marine, living near the sea bed at depths down to 3,000 m (9,800 ft) or more.[4]

Diversity

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Families

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Four extant and five extinct families of rajoid have been described:[5][6][7]

Formerly, some Rhinopristiforms were also included.

The smooth skates, the Anacanthobatidae, contain a single genus, Anacanthobatis, of about 10 species. They are small fish living on the continental slopes of tropical and subtropical waters, and are native to Natal, South Africa, tropical West Africa, and Taiwan. Smooth skates have a filament extending from a rounded protuberance on the snout. Both the dorsal and ventral surfaces are smooth and have no dermal denticles. The tail is slender and a little shorter than the body. No dorsal fins are present and the caudal fin is small and membranous.[8]

Raja texana, the roundel skate

The skate family Rajidae contains 14 genera and around 200 species. They are found worldwide, but are relatively uncommon near coral reefs and in shallow tropical seas. A few species occur in brackish water. The disc shape is rhomboidal, and the tail long. Two dorsal fins are found and the caudal fin is much reduced. The pelvic fins have two lobes. Most species have rough skins with dermal denticles which are especially obvious along the spine. The eggs are laid in a protective hard case with string-like elongations at the four corners.[9]

The extinct families Sclerorhynchidae and Ptychotrygonidae had long, serrated rostrums very similar to those of extant sawsharks and sawfishes, and their relation to them has been debated. A 2004 study found sawsharks to actually be the most basal of batoids rather than true sharks, with the order Sclerorhynchiformes containing Sclerorhynchidae and Ischyrhizidae and forming a sister group to sawfish and all other rays, with the clade containing sawsharks and rays being coined Pristiorajea.[10][11] However, further studies have affirmed that sawsharks are true sharks and a member of Selachimorpha. Later studies have instead found Sclerorhynchiformes to form a sister group to Rajidae, and thus downgraded it to being the suborder Sclerorhynchoidei of the order Rajiformes.[7][12][13][14]

Biology

[edit]
Skates have an electric organ in the tail. They use it to generate a weak electric field to locate their prey.[15]

In most rajoids, water for breathing is taken in through the spiracles rather than through the mouth and exits through the gill slits. Most species swim by undulating their enlarged pectoral fins, but the guitarfish propel themselves through the water with sideways movements of their tail and caudal fin. Most species are carnivores, feeding on molluscs and other invertebrates on the sea bed, and small fish, but the manta ray feeds on plankton sieved out of the water as it swims by its wide open mouth. Some species are viviparous, others ovoviviparous (both giving birth to live young), but the skates lay eggs in horny cases known as mermaid's purses.[citation needed] Most species are benthic, resting on the sandy or muddy sea bed, sometimes undulating their pectoral fins to stir up sediment and bury themselves shallowly. Others are pelagic and continually cruise the ocean.[4]

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Rajiformes

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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. These batoids exhibit powered by their pectoral fins and possess ventrally positioned gill slits, with most being oviparous and laying leathery cases. Rajiformes represent the most speciose group of elasmobranchs, encompassing approximately 305 valid across four families—Rajidae, Arhynchobatidae, Gurgesiellidae, and Anacanthobatidae—making up nearly half of all batoid diversity. 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 venturing into brackish or freshwater systems. They are distributed globally across all oceans, with highest diversity in the North Atlantic and regions, where often exhibit restricted ranges contributing to elevated and vulnerability to localized threats. Morphologically, Rajiformes display a depressed trunk, firm rostral in most taxa, and defensive features such as thorns or spines along the and disc margins, particularly in males during breeding; their diet consists mainly of bottom-dwelling and small fishes captured via suction feeding. The evolutionary history of Rajiformes traces back to the , approximately 200 million years ago, with the order forming a monophyletic clade within Batoidea that has diversified significantly, especially in deep-water habitats. Conservation concerns are prominent, as over one-third of skate species face risks due to in fisheries, habitat degradation, and slow life histories characterized by late maturity and low ; notable examples include large-bodied species like the common skate (Dipturus batis), now critically endangered in parts of its range. Ongoing taxonomic revisions, informed by , continue to refine family boundaries and species counts, underscoring the order's ecological importance in marine food webs as both predators and prey.

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). This placement reflects their monophyletic grouping within elasmobranchs, where Batoidea diverged from shark-like ancestors (Selachimorpha) early in chondrichthyan evolution. Within Batoidea, Rajiformes is often positioned as the sister group to the remaining batoid orders, supported by both morphological and molecular phylogenies. 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. 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 . 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. 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. 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. These fossils indicate an early diversification within Batoidea, with Rajiformes emerging alongside the initial radiation of flattened-bodied chondrichthyans. Recent molecular studies reinforce the of Rajiformes, utilizing markers such as subunit I (COI) and subunit 2 (ND2). For instance, analyses of concatenated mtDNA sequences from over 400 Atlantic skate specimens via maximum likelihood and methods confirm robust clustering of Rajiformes families (e.g., Rajidae, Arhynchobatidae), supporting their cohesive evolutionary lineage within Batoidea. Similar mitogenomic phylogenies from complete mitochondrial genomes of multiple skate species further validate this monophyly, highlighting genetic divergence from other batoid orders post-Jurassic.

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". 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. 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 , emphasizing their cartilaginous skeleton and gill structure as distinguishing features from bony fishes. This work laid foundational 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 , continued to classify skates and rays within Elasmobranchii without a dedicated order, often lumping them with based on morphological similarities like and . 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. 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. As of 2025 updates in authoritative databases, Rajiformes remains a valid order encompassing skates, recognized by the (WoRMS) with Berg's 1940 authorship intact. Ongoing molecular evidence supports the 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. 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. 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. 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. 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. 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.

Morphology and Anatomy

Body Structure

Rajiformes, commonly known as skates, exhibit a distinctive dorsoventrally flattened 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. 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 (Beringraja binoculata). 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. 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. 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. 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. Skin morphology in Rajiformes contributes to both and concealment. The dorsal surface is typically covered with dermal denticles or enlarged thorns, often arranged in rows along the midline, , and orbits, providing defense against predators. In contrast, the ventral skin is smooth and lacks prominent denticles, facilitating smoother interaction with the substrate. Coloration features mottled patterns of browns, grays, and whites on the dorsal side, enabling effective against sandy or muddy seabeds, while the paler ventral surface aids in . 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.

Sensory and Locomotory Adaptations

Rajiformes exhibit specialized electroreceptive capabilities through the , 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. 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 . 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 or evasion. 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. 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.

Distribution and Habitat

Global Range

Rajiformes exhibit a , inhabiting all major ocean basins from polar to tropical regions. Species occur across the Atlantic, Pacific, Indian, and Oceans, as well as the surrounding . For instance, the Arctic skate (Amblyraja hyperborea) is widely distributed in circumpolar Arctic waters, extending from the to the and across to the Pacific and Indian Oceans at high latitudes. In contrast, Eaton's skate (Bathyraja eatonii) is representative of southern polar distributions, commonly found on the , around the South Orkney and , and along the . 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. This latitudinal bias reflects adaptations to benthic lifestyles in mid- to high-latitude environments, though some taxa extend into subtropical areas. 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. Endemism patterns underscore regional specialization, with elevated diversity and unique assemblages in semi-enclosed or isolated basins. The hosts several endemic skates, contributing to its status as a hotspot for restricted-range species amid high overall elasmobranch richness. Similarly, the Southwest Atlantic features notable , with approximately 32 skate species, many confined to shelf and slope habitats from southern to , highlighting localized evolutionary divergence.

Environmental Preferences

Rajiformes species predominantly inhabit benthic environments characterized by soft-bottom substrates such as and , which facilitate burial for and predation. These substrates allow skates and rays to blend into the seafloor, reducing visibility to predators and prey, with undulations of their pectoral fins stirring to enhance concealment. 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. Temperature tolerances among Rajiformes vary by habitat and , with the majority of temperate and polar thriving in cool waters ranging from 0°C to 20°C. For instance, deep-water skates like Bathyraja parmifera are commonly found in near-bottom temperatures of 0–3°C. Some subtropical representatives, such as the clearnose skate (Rostroraja eglanteria) in the family Rajidae, tolerate temperatures up to 27°C in shallow coastal zones. Recent climate studies from the 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. Most Rajiformes are strictly marine, adapted to full oceanic levels around 35 ppt, though some rajids exhibit capabilities, tolerating brackish estuarine conditions down to 12 ppt. Species like the clearnose skate (Rostroraja eglanteria) demonstrate partial euryhalinity, enabling occasional incursions into estuaries for foraging or refuge. Regarding oxygen, Rajiformes generally avoid hypoxic zones with dissolved oxygen below 2 mg/L, as these conditions impair function and metabolic rates, prompting behavioral relocation to better-oxygenated areas. Migratory behaviors in Rajiformes are closely linked to environmental gradients, particularly seasonal shifts in and substrate availability for spawning. 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. For example, thornback rays (Raja clavata) exhibit clear cycles of inshore migration for reproduction between and , driven by cues exceeding 10°C. These movements ensure alignment with peak productivity periods while avoiding extremes in or oxygen depletion.

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. 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 , highlighting ongoing taxonomic discoveries facilitated by advanced molecular and morphological analyses. Patterns of in Rajiformes reveal hotspots concentrated in the Indo-West Pacific, where approximately 40% of known occur, reflecting the region's role as a center of marine biodiversity. High is evident in isolated habitats, such as seamounts and polar regions; for instance, several Bathyraja are restricted to seamounts and shelves, comprising up to 20% of local batoid assemblages in these areas. The family Rajidae accounts for about 50% of total Rajiformes diversity, largely due to adaptive in cold-water environments that promote morphological and ecological divergence. Evolutionary trends in Rajiformes trace a major radiation during the , coinciding with global cooling and tectonic changes that expanded habitats suitable for benthic lifestyles. 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. Conservation assessments underscore threats to this diversity, with approximately 30% of Rajiformes classified as by the IUCN due to limited distributional and population data, complicating risk evaluations. As of 2021, approximately 33% of assessed elasmobranch , including many skates, are classified as threatened (Critically Endangered, Endangered, or Vulnerable) by the IUCN, with ongoing increases driven by in deep-sea fisheries and degradation in hotspots.

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 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 rostral supporting the , 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 and habitat degradation. The Arhynchobatidae, or softnose skates, are a diverse family with around 104 in 13 genera, featuring softer snouts without prominent rostral , 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 characterizes this group, with many restricted to seamounts or oceanic islands; examples include Bathyraja irrasa from the North Pacific, vulnerable due to limited range and . 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 and are often due to rarity in collections; a representative is Gurgesiella atlantica from the western Atlantic, assessed as least concern but with sparse data. 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 in tropical to temperate waters at depths of 150-1,600 meters over soft substrates, they represent an adaptation to abyssal environments. and small size (up to 66 cm total length) are typical, as seen in Anacanthobatis melanosoma, which occurs in the slope habitats. Morphological gradients across these families reflect ecological specializations, from the disc-dominant, benthic forms of Rajidae in cold, deep settings to the reduced, leg-like structures of Anacanthobatidae in abyssal , with Arhynchobatidae and Gurgesiellidae showing intermediate adaptations for slope and shelf environments.

Biology and Ecology

Reproduction and Development

Rajiformes exhibit , laying eggs encased in leathery capsules known as mermaid's purses. These capsules, typically containing one per case in most , protect the developing and are deposited on the seafloor in benthic habitats; however, certain like the (Beringraja binoculata) can have up to eight embryos per capsule, with two being the most common. Mating in Rajiformes involves internal fertilization facilitated by male claspers, paired structures that transfer during , which may include biting or pectoral fin displays in skates. Breeding is often seasonal, with peaks in spring and summer for temperate species; for example, the (Raja clavata) spawns primarily from May to January, peaking in August. 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. Embryonic development in oviparous Rajiformes proceeds directly to without a free-living larval stage, relying on yolk-sac absorbed over the . Incubation times range from 2 to 12 months depending on and ; 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. is reached at 3–15 years, varying by and size; for example, the little skate (Leucoraja erinacea) attains 50% maturity at about 9.5 years for females, while some smaller mature in 3–4 years.

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 , including crustaceans (such as shrimps, crabs, and amphipods), mollusks, worms, and cephalopods, supplemented by small fishes. Skates in the family Rajidae often use a specialized feeding mechanism involving hyostylic protrusion, where the upper extends forward to create suction for capturing buried prey like worms and crustaceans directly from the substrate. Foraging behaviors in Rajiformes emphasize energy-efficient predation suited to their ectothermic . Many , particularly skates and stingrays, adopt 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 during low-light periods to reduce predation risk and exploit prey availability; for instance, deep-water skates show increased consumption of crustaceans and at night. Deep-sea forms, such as certain Bathyraja , also engage in opportunistic scavenging, feeding on carrion that sinks to the seafloor, which aligns with their low metabolic rates and infrequent feeding cycles. Social behaviors among Rajiformes are generally subdued, reflecting their solitary or loosely affiliative lifestyles. Adults are typically solitary , 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.

Conservation and Human Interactions

Threats and Status

Rajiformes, comprising skates and related taxa, face severe threats primarily from , with 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 rates from stress and injury. Targeted fisheries exacerbate declines, particularly for skate wings used in food markets, leading to population reductions of up to 90% in heavily exploited regions. degradation from 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 at 36% threatened due to their to . Iconic species such as the common skate (Dipturus batis) are Critically Endangered, reflecting drastic declines from historical . Around 13% of species remain , largely owing to challenges in monitoring deep-sea populations and limited survey data in remote habitats. These low reproductive rates, characterized by slow growth and late maturity, amplify susceptibility to even moderate 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. impairs embryonic development in egg-laying species by weakening egg cases and reducing hatchling viability, particularly when combined with elevated temperatures. These effects are pronounced in biodiversity hotspots, where synergistic stressors intensify risks for already depleted populations. Regional variations highlight uneven threats, with severe in the North Atlantic leading to local extinctions of large-bodied skates from intensive trawl and longline fisheries. In the , species often exhibit restricted ranges contributing to elevated and vulnerability to localized threats.

Fisheries and Management

Rajiformes , particularly skates, are exploited in global fisheries primarily for their , 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., and Dipturus species) contributing around 20,000-30,000 tons annually. Management strategies for Rajiformes fisheries include total allowable catches (TACs) and quotas established by the since 2010, such as limits on Dipturus species in the and to prevent of vulnerable stocks, with exemptions for certain protected skates like the common skate (Dipturus batis). 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 and supporting stability through no-take zones. Monitoring techniques in Rajiformes fisheries rely on genetic barcoding of the mitochondrial COI gene to accurately identify in mixed catches and processed products, as demonstrated in retail surveys across the and where mislabeling was prevalent. Acoustic tagging has also been employed to study movement patterns, with (Raja clavata) individuals tracked in Portuguese MPAs to inform spatial and reveal seasonal migrations over several kilometers. These methods enhance and assessments by distinguishing cryptic and quantifying impacts. The (Raja clavata) has shown signs of partial recovery in the , potentially aided by interim conservation measures and the planned inshore 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 , where unregulated high-seas fisheries lead to continued declines in deep-water skates, with inadequate reporting and enforcement exacerbating in areas like the ' .

References

  1. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/rajiformes
  2. https://researcharchive.calacademy.org/research/ichthyology/catalog/SpeciesByFamily.asp
  3. https://www.mdpi.com/1424-2818/16/12/709
  4. https://pmc.ncbi.nlm.nih.gov/articles/PMC8303890/
  5. https://www.fao.org/4/x2401e/x2401e07.pdf
  6. https://www.tandfonline.com/doi/full/10.1080/14772019.2018.1486336
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