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Sand devil

The sand devil (Squatina dumeril), also known as the Atlantic angel shark, is a of angel shark belonging to the family Squatinidae, characterized by its flattened body and broad pectoral fins that give it a ray-like appearance, enabling it to burrow into sandy or muddy substrates on the ocean floor. Native to the northwestern , it inhabits coastal and continental shelf waters from southern , (including the ) southward to northern (), typically at depths ranging from shallow nearshore areas to over 1,290 meters on the upper slope, where it prefers soft-bottom . This benthic predator grows to a maximum length of approximately 152 cm, with a coloration of bluish-gray to ashy-gray (fading to brown in preservation) and a white ventral surface, often lacking distinct spotting in adults. Ovoviviparous, it gives birth to litters of up to several pups after internal development, feeding primarily on small bottom-dwelling fishes, crustaceans, and that it ambushes from concealment. Once more abundant, populations have declined due to in trawl fisheries and habitat degradation, leading to its classification as Least Concern on the (assessed 2017), with ongoing research highlighting genetic structuring into distinct groups across the Atlantic and Gulf regions to inform conservation efforts.

Taxonomy

Classification

The sand devil (Squatina dumeril) belongs to the kingdom Animalia, phylum Chordata, class Chondrichthyes, order Squatiniformes, family Squatinidae, genus Squatina, and species Squatina dumeril. This species was first described by Charles Alexandre Lesueur in 1818, based on specimens collected from the western Atlantic Ocean. It has been recognized as a valid taxon without major taxonomic revisions since its original description. Historical confusions with other Squatina species have been resolved through morphological examinations and genetic analyses, confirming its distinct status. Molecular phylogenetic studies using mitochondrial markers such as and 16S rRNA place S. dumeril in a western North Atlantic , showing from sister species like Squatina californica.

Etymology and synonyms

The common name "sand devil" for Squatina dumeril derives from the species' predation strategy, in which it burrows into sandy substrates to lie in wait for prey, combined with its aggressive, snapping behavior when captured by workers, evoking a "devilish" temperament even out of water. The genus name Squatina originates from the Latin term for a type of , reflecting the angel sharks' superficial resemblance to skates or rays. The specific epithet dumeril honors the French zoologist (1774–1860), whom the describer Charles Alexandre Lesueur acknowledged for his support of natural sciences research. Historically, S. dumeril has been subject to taxonomic confusion in regional records, with Squatina heteroptera (described from the ) and Squatina mexicana now recognized as junior synonyms, based on morphological and distributional overlap confirming conspecificity. Spelling variants in early literature, such as Rhina dumeril, Rhina dumerili, and Rhina dumerilii, also refer to this species but stem from nomenclatural inconsistencies rather than distinct taxa. Phylogenetically, S. dumeril forms a sister species pair with the Pacific angel shark (Squatina californica), reflecting a transisthmian geminate relationship; their divergence is estimated at approximately 6.1 million years ago, coinciding with the uplift of the that separated Atlantic and Pacific marine faunas. This timeline emerges from analyses calibrated against fossil records and geological events. Within the Squatinidae family, the of the genus Squatina—including S. dumeril—is robustly supported by mitochondrial genetic markers such as subunit I (COI) and (16S rRNA), which resolve four major geographic clades with high bootstrap support.

Description

Morphology

The sand devil, or Atlantic angel shark (Squatina dumeril), possesses a distinctive flattened, ray-like body that facilitates its benthic existence, characterized by broad pectoral and pelvic fins that extend laterally to form wing-like structures. These fins are posteriorly angular and integrate seamlessly with the body disc, creating a discoid outline typical of angel sharks. Unlike typical sharks, the sand devil lacks an anal fin, but features two small, equal-sized dorsal fins positioned posteriorly near the tail base. The head region is notably specialized, with a terminal mouth equipped with sharp, pointed teeth arranged in three rows in the upper (totaling approximately 20 teeth) and a similar number in the lower (approximately 18 teeth), conical with broad bases and smooth edges, for securing prey. Large spiracles, positioned behind the dorsally located eyes, enable efficient water flow over the gills, while nasal barbels and spines on the snout and above the eyes enhance sensory and protective functions. The body surface is covered in dermal denticles, or thorns, which are conical and slightly recurved, distributed evenly on the dorsal side with larger clusters around the eyes and along the midline and edges for structural reinforcement. The tail is short and stout, terminating in an asymmetrical caudal fin with distinct upper and lower lobes that provide maneuverability. This muscular tail structure supports rapid, undulating movements. Sensory adaptations include the , electroreceptive pores distributed across the head and ventral surface, which detect weak electric fields generated by nearby organisms.

Size, weight, and coloration

The sand devil exhibits notable in size, with females growing larger than males and attaining a maximum total length of 1.52 m, while common adult sizes range around 1 m total length. Males typically reach smaller maximum lengths, and both sexes possess claspers in males for , a characteristic feature of elasmobranch . Adult individuals generally weigh 8–12 kg, with the largest recorded specimens up to approximately 30 kg (based on length-weight relationships). is reached at around 92 cm TL for males and 107 cm TL for females. The surface displays a mottled gray to brown coloration, often featuring dark spots and blotches that provide effective against sandy seafloor substrates, while the ventral side is paler for concealment from below. Fresh specimens appear bluish gray or ashy gray , transitioning to chocolate brown in preservatives, with the underside white and occasional red spots on the , , and . Young sand devils show faint symmetrical white spotting on the surface, which fades in adults. Growth in the sand devil is characterized by rapid juvenile development, slowing significantly after reaching around 85–100 cm total length. This pattern aligns with the ' benthic lifestyle, where larger body size enhances predation efficiency once maturity is achieved.

Distribution and habitat

Geographic range

The sand devil (Squatina dumeril) has a primary geographic range in the northwestern , extending from off the coast of southward along the eastern seaboard of the to the , and into the northern , including waters off and . This distribution spans latitudes from approximately 43°N to 25°N and longitudes from 96°W to 70°W, encompassing and upper environments. The species occurs at depths ranging from 1 to 1,375 meters, typically associated with shallower habitats up to 128 meters, though confirmed records extend to 1,390 meters. Historical reports suggest possible extensions into the , including off the coasts of , , and , but these are likely misidentifications with other Squatina species, such as S. david in Colombian waters, contributing to uncertainty regarding the southern limit due to ongoing taxonomic confusion. Recent sources confirm presence in the northern , such as off , . No major range contractions have been noted between historical and current distributions, though gaps persist in survey for deeper waters beyond the typical shelf depths. Seasonal s briefly influence occupancy within the core , with individuals shifting to deeper offshore areas in winter.

Habitat preferences and patterns

The sand devil inhabits soft-bottom environments on the continental shelf and upper slope, preferring sandy or muddy substrates that allow it to and itself while ambushing prey. It occurs at depths from 1 to 1,375 m but shows a preference for shallower coastal areas during warmer periods, with records from 4 to 250 m in its northern range. This species undertakes seasonal migrations, shifting inshore to shallow coastal waters (<35 m) during spring and summer, including summer and fall residency in areas such as the lower Chesapeake Bay, before moving to deeper offshore waters (>90 m) in winter and early spring. These movements align with its overall western North Atlantic distribution from to northern . Knowledge of the sand devil's deep-water habitat use remains limited due to sampling difficulties at greater depths and a lack of recaptures (0 out of 170 tagged individuals) in long-term monitoring programs.

Biology

Reproduction and development

The sand devil (Squatina dumeril) exhibits aplacental , a reproductive mode in which embryos develop internally and are nourished primarily by a , without a placental connection to the mother. occurs via the male's claspers, which transfer sperm to the female during copulation. Evidence of aligns with a spring mating season, coinciding with peak development. The reproductive cycle is at least , and females have only one functional (the left). Gestation lasts approximately 12 months, after which females give birth to live young. Litter sizes range from 4 to 25 pups, with larger females producing more offspring on average; births typically occur from February to June. is reached at total lengths of 86–93 cm, with females maturing slightly earlier in size than males. Pups are born fully formed at 23–27 cm total length, capable of immediate and predatory upon emergence. Larger females may support greater reproductive output, influencing potential sizes in subsequent cycles.

Diet and feeding habits

The sand devil (Squatina dumeril) is an that primarily forages by lying buried in the sandy or muddy seafloor, emerging with sudden upward strikes to capture prey using its powerful jaws equipped with sharp teeth adapted for grasping. This strategy allows it to target demersal and benthic organisms while minimizing energy expenditure in its sedentary lifestyle. Stomach content analyses reveal that its diet is dominated by fishes, which account for 93.4% of the Index of Relative Importance (IRI), supplemented by cephalopods at 4.7% IRI and crustaceans at 1.9% IRI. Key fish prey include (Micropogonias undulatus) and (Peprilus burti), with (Loligo sp.) serving as a significant secondary item. Ontogenetic shifts occur in the sand devil's diet, with juveniles under 550 mm total length consuming more smaller invertebrates such as squid (63.0% IRI) and minor fish like hake and cusk-eels, reflecting their limited gape size. As individuals grow to 550–800 mm, the diet incorporates larger teleosts like Atlantic croaker (25.7% IRI), while adults over 800 mm preferentially target butterfish (28.9% IRI) alongside continued squid intake (40.4% IRI). These changes align with increasing body size and gape width, enabling the consumption of progressively larger prey, and result in a narrowing dietary niche breadth from 0.50 in juveniles to 0.43 in adults. Prey selection generally favors items less than 30% of the shark's total length, ensuring efficient capture. Seasonal variations influence feeding, with higher consumption in winter (40.9% IRI) likely due to deeper shifts and prey availability, compared to spring and fall when dominate (47.3% IRI and 43.6% IRI, respectively). Dietary niche breadth is narrowest in winter (0.40), indicating specialization, and broadest in fall (0.63).

Ecology and behavior

Predatory strategies and prey interactions

The sand devil (Squatina dumeril), also known as the Atlantic angel shark, is an that relies on and stealth to capture prey. It buries itself in soft sediment on the seafloor, leaving only its eyes, spiracles, and portions of its surface exposed to blend seamlessly with the benthic environment. This positioning allows it to remain undetected while awaiting the passage of demersal prey species, such as small fishes and cephalopods. Prey detection primarily occurs through electroreception, facilitated by an abundance of specialized pores () concentrated on the ventral surface, which sense the weak bioelectric fields produced by nearby prey movements—even in turbid or dark conditions. Complementary mechanoreception via the system detects vibrations from prey, enabling precise localization. Once detected, the sand devil launches a swift upward strike from a buried position. This selective predation exerts pressure on local benthic populations, promoting in coastal ecosystems. Occupying a mid-level carnivore trophic position of approximately 4.1, the sand devil influences dynamics by controlling abundances of smaller demersal species, though its own predators include larger elasmobranchs, such as and rays, and marine mammals; incidental human capture via further impacts populations. Limited research exists on juvenile predation dynamics, where smaller individuals likely use analogous tactics but exhibit heightened vulnerability due to reduced size and sensory acuity.

Social structure and daily activity

The sand devil, or Atlantic angel shark (Squatina dumeril), exhibits a largely solitary , with individuals typically avoiding prolonged interactions except during brief encounters. Observations across angel shark species indicate no evidence of schooling or established territoriality, though loose aggregations may form in areas of high prey density. These groupings appear opportunistic rather than structured, driven by resource availability rather than social bonding. Recent genetic studies (as of ) indicate population structuring across regions, but data on social interactions remain limited. Activity patterns in the sand devil are not well-documented, but likely involve periods of during and hunting aligned with prey activity, potentially occurring both day and night. Individuals bury themselves in sandy or muddy substrates for and . Limited telemetric data on angel sharks suggest relatively small home ranges in coastal areas, but specific information for S. dumeril is lacking. In response to disturbances, such as approaching predators or human activity, the sand devil employs rapid into the or brief, explosive swims to evade threats, typically covering short distances before resuming . Data on deep-water behavior remains sparse due to challenges in direct observation and tagging in such environments, limiting understanding of potential variations in activity rhythms beyond shallow coastal zones.

Human interactions and conservation

Fisheries, bycatch, and economic value

The sand devil (Squatina dumeril) is primarily encountered as bycatch in bottom trawl fisheries targeting penaeid shrimp and demersal species such as butterfish in the northwestern Atlantic, particularly the Gulf of Mexico. It may also be incidentally captured in gillnets and longlines operated for other demersal fish, though at lower frequencies. Due to its demersal habits and flattened body, it is vulnerable to these gear types but is not targeted commercially or recreationally. Incidental catch rates remain low, typically comprising less than 1% of total landings in observed trawl operations; for example, extrapolated in the U.S. penaeid fishery totaled approximately 279 kg across sampled hauls from 2011–2016. This reflects the species' relative rarity in catches and its small maximum size (up to 152 cm total length), which limits directed effort. The economic value of the sand devil is minimal, with edible flesh occasionally retained for local consumption but rarely marketed due to low demand and poor flesh quality compared to targeted species. Fins are not utilized in the shark fin trade, as the species yields insufficient volume, and overall utilization is negligible. In the United States, the sand devil is managed as a highly migratory under the Magnuson-Stevens Fishery Conservation and Management Act through the Atlantic Highly Migratory Species Fishery Management Plan, where it has been prohibited from retention in commercial and recreational fisheries since 1999 as a precautionary measure to prevent . No specific quotas apply, but is monitored via observer programs in multispecies fisheries, with requirements for live release when encountered. Regulatory prohibitions and enhanced gear selectivity, such as the mandatory use of reduction devices in trawls implemented in the , contribute to management efforts.

Conservation status and threats

The sand devil (Squatina dumeril) is currently assessed as Least Concern by the International Union for Conservation of Nature (IUCN), with the evaluation completed in June 2017 and reaffirmed in the 2019 Red List update, remaining unchanged through 2025. This status reflects its broad distribution across the western North Atlantic and relatively low direct exploitation pressures compared to other angel . Population trends for the species lack comprehensive quantitative data, as large-scale abundance surveys are limited; however, the IUCN assessment indicates low risk without evidence of widespread decline. Shallow coastal nurseries may represent a point of vulnerability, where juveniles could face localized pressures, though overall resilience is inferred from the species' ability to inhabit deeper waters (up to 1,375 m). Key threats to the sand devil include degradation in coastal zones from activities like for channels, which can disrupt benthic substrates essential for predation. Pollution from and industrial discharges further exacerbates risks in nearshore areas, potentially affecting and prey availability. poses additional challenges, with ocean warming potentially altering migration patterns and range distributions as temperatures shift suitable habitats poleward. Significant knowledge gaps persist, including outdated confirmations of the species' southern range extent in the and , where recent sightings are sparse. Insufficient deep-water surveys hinder understanding of offshore populations, and although a 2024 genetic study has identified distinct population structure in U.S. waters, further assessments are needed to delineate connectivity among regional groups. Conservation measures include protections within marine sanctuaries such as the Flower Garden Banks National Marine Sanctuary in the northwestern , where the species occurs and benefits from no-take zones for certain activities. Ongoing monitoring is recommended through NOAA Fisheries reports, emphasizing reduction and assessments to inform future management.

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