Little sleeper shark
(Somniosus rostratus)

Somniosus rostratus (Risso, 1826)

Other scientific names recently used

Somniosus  bauchotae  (Quero, 1976)


Diagnosis

A moderately-sized, rather slender shark with two small, low spineless dorsal fins; no anal fin and a small keel present upon the ventral lobe of the caudal fin below the lateral line on the peduncle. Lower caudal lobe relatively long. Head short, with broadly-rounded snout and comparatively small eyes, with prominent spiracles just behind them; teeth fairly large with semi-oblique cusps. Skin feels rather smooth. Colour dark grey, brown or olive-brown; no obvious fin markings.


Size

To about 140cm TL; size at birth between 21 and 28cm. Most specimens typically to 100cm.


Status and Distribution

N.E. Atlantic: Infrequent or rare. Northerly limit of range uncertain; recorded from off N.W. Ireland at ca. Latitude 55-56N; also in Bay of Biscay, off Portugal and Madeira; southwards in deep water off the N.W. African coast south to the Canary Islands; southerly range limit unclear.
Mediterranean Sea: Infrequent or rare; Western Mediterranean with known capture-sites including deepwater along the Cote d'Azur, Ligurian Sea, Eastern Sicily and Algeria. Apparently not yet recorded from Malta but a likely addition to their elasmobranch fauna. Probably extremely scarce or even absent eastwards of the Ionian Sea.


Biology

This little-known deepwater shark is probably benthopelagic, rather than benthic, based upon its specialised heterocercal tail which is markedly different from both coastal and deepwater benthic species. The presence of caudal keels also suggest adaptions for active predation upon mobile prey, rather than a sedentary habit as displayed by its larger congener, S. microcephalus. The little sleeper shark occurs at depths of 400+ metres in Atlantic waters and between 250 to 1000m in the Mediterranean, near to or on the seabed, both offshore and in deep coastal waters such as the Ligurian Sea. A predator of deepwater telosts and invertebrates, little is known of its feeding habits. Ovoviviparous, with between nine and seventeen embryos found in Mediterranean females. Females mature from 82 to 134cm TL; males from 71 cm.