| Sand devil | |
|---|---|
 | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Subclass: | Elasmobranchii |
| Division: | Selachii |
| Order: | Squatiniformes |
| Family: | Squatinidae |
| Genus: | Squatina |
| Species: | S. dumeril |
| Binomial name | |
| Squatina dumeril Lesueur, 1818 | |
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| Range of the sand devil[1] | |
Thesand devil orAtlantic angel shark (Squatina dumeril) is aspecies ofangelshark,family Squatinidae, native to the northwesternAtlantic Ocean. It occurs off the easternUnited States, in the northernGulf of Mexico, and possibly in parts of theCaribbean Sea. Thisbottom-dwelling shark is found in shallowinshore waters in summer and fall, and deep offshore waters in winter and spring. The sand devil's flattened body and enlargedpectoral andpelvic fins give it aray-like appearance. There is a band of enlarged thorns running along the middle of its back. It is gray or brown in color, with scattered small dark spots. This species reaches 1.2–1.5 m (3.9–4.9 ft) in length.
The diet of the sand devil consists mainly of smallteleost fishes andsquid, which are captured viaambush attack. This species isviviparous, with the unborn young nourished by theiryolk sacs. Females have a multi-year reproductive cycle and give birth to 4–25 pups in spring or early summer, following a 12-monthgestation period. The sand devil is not aggressive, but may attempt to bite if harassed or captured. Though not valued economically, it iscaught incidentally bycommercialbottom trawlfisheries.
FrenchnaturalistCharles Alexandre Lesueur described the sand devil in an 1818 volume ofJournal of the Academy of Natural Sciences of Philadelphia. Previously, it had been regarded as the same species as the EuropeanSquatina squatina. Lesueur based his account on an adult male 1.2 m (3.9 ft) long caught off the eastern United States, and named the species in honor ofAndré Marie Constant Duméril.[2]
Phylogenetic analysis, based onmitochondrial DNA, has concluded that the sand devil and thePacific angel shark (S. californica) aresister species. The two of them in turn form aclade with other angel sharks found in theAmericas.Molecular clock estimation has timed thedivergence ofS. dumeril andS. californica atc. 6.1Ma, around the time that theIsthmus of Panama formed. The rise of the Isthmus likely split the ancestral angel shark population, leading to their becoming separate species.[3]
The sand devil has a flattened, moderately narrow body with greatly enlargedpectoral andpelvic fins. The skin folds along the sides of the head have smooth margins, without lobes. The large eyes are placed on top of the head and have prominentspiracles behind. The nostrils bear thin, pointedbarbels with smooth or slightly fringed margins. The wide mouth is positioned terminally on the head. The jaws contain 10 upper and 9 lower tooth rows on each side, with toothless gaps at the middle. Each tooth has a broad base and a single pointed cusp with smooth edges. There are five pairs ofgill slits located on the sides of the head.[4][5]
The pectoral fins are broad and angular with narrow rear tips; the front of the pectoral fin is separate from the head, forming a triangular lobe. The twodorsal fins are similar in size and shape, and are positioned far back on the body. Theanal fin is absent. The lower lobe of thecaudal fin is larger than the upper. Thedermal denticles have rounded bases and three horizontal ridges. There is a distinctive band of larger thorns running along the midline of the back, from the nape to thecaudal peduncle. The dorsal coloration varies from greenish or bluish gray to reddish brown, with a scattering of small, darker spots and sometimes irregular splotches; the underside is uniformly pale. This species reaches 1.3–1.5 m (4.3–4.9 ft) in length and at least 16 kg (35 lb) in weight.[4][5]
The sand devil is found in the northwesternAtlantic Ocean fromMassachusetts to theFlorida Keys, where it is fairly common. It also occurs in the northernGulf of Mexico, and there are additional unconfirmed records fromCuba,Jamaica,Nicaragua, andVenezuela. The southern extent of its range is uncertain due to confusion with thedisparate angelshark (S. heteroptera) andMexican angelshark (S. mexicana). Because they inhabit deep-waters and because of their low commercial value the effort put into data collection is low, as with many species under these circumstances. Although their appearances are fragmented they still are classified under large broader spaces due to the lack of research done. As a result, ranges of deep-water shark species are often considered continuous across broad expanses despite records of occurrence, in many cases, being spatially fragmented.[6] Thisbottom-dwelling shark is found over sandy or muddy bottoms on thecontinental shelf andslope.[4]
Off the easternUnited States, the sand devil has been documented tomigrate seasonally. In the summer, it moves towards the shore to depths of less than 35 m (115 ft), and many can be found in water only meters deep. During fall it can be foundinshore, down to a depth of 90 m (300 ft). In winter and spring, it is found around the outer continental shelf at depths greater than 90 m (300 ft); individuals have been recorded as far as 140 km (87 mi) from land and 1,290 m (4,230 ft) deep.[4]
The sand devil is anambush predator that spends much time buried in the bottomsediment. Its diet consists mainly ofdemersalteleost fishes such ascroakers,goatfishes, andbutterfishes. However, some types of demersal fishes such asjacks are rarely eaten, perhaps because they are more active and thus likely to escape attacks.Squid are a major secondary food source, particularly for smaller sharks.Crabs,shrimp,mantis shrimp,skates, andbivalves are infrequently eaten.[4][7] This species feeds both during the day and at night. It tends to select prey approximately 50–60% as long as its mouth is wide; this size is consistent with what is predicted fromoptimal foraging theory to yield the most efficient rate ofenergy return. The variety of prey taken is greatest in fall and least in winter, and smaller sharks have a more varied diet than larger ones.[7] In the northern Gulf of Mexico, the most important prey species areAtlantic croaker (Micropogonias undulatus),longspine porgy (Stenotomus caprinus),spot croaker (Leiostomus xanthurus),Gulf butterfish (Peprilus burti),red goatfish (Mullus auratus),dwarf goatfish (Upeneus parvus), andlongfin inshore squid (Doryteuthis pealeii). The relative importance of each differs across seasons (for example, squid are more important in winter), perhaps due to seasonal variation in their availability.[7][8] A knownparasite of the sand devil is thecopepodEudactylina spinula.[9]
Like other angel sharks, the sand devil isviviparous with the developingembryos sustained byyolk. Mature females have one functionalovary, on the left, and two functionaluteruses.Mating occurs in the spring; adult males have spines on the outer margins of their pectoral fins, which may help in gripping the female duringcopulation.[10] Females reproduce no more than once every two years, perhaps longer. Litter size varies from four to 25 pups, and does not appear related to the size of the female. Thegestation period lasts roughly 12 months, and birthing occurs between February and June at depths of 20–30 m (66–98 ft).[4][10] The newborns measure 25–30 cm (9.8–11.8 in) in length. Males and femalessexually mature at around 93 and 86 cm (37 and 34 in) long respectively; the fact that females mature at a smaller size than males is unusual among sharks.[10]
Though not normally aggressive towards humans, the sand devil can inflict serious wounds if provoked. Itscommon name refers to its habit of snapping vigorously atfishery workers when caught, and even out of the water it is capable of lunging upwards to bite.[4][5] This shark iscaught incidentally inbottom trawls operated bycommercial fisheries targeting other species. It is edible but seldom brought to market.[4] TheInternational Union for Conservation of Nature (IUCN) presently rates this species asleast concern.[1]
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