Pacific sleeper shark - Somniosus pacificus


Illustration © Marc Dando

A giant sleeper shark with a short, rounded snout, heavy cylindrical body, and small precaudal fins. Its skin is rough and bristly, with denticles with strong hooklike erect cusps. It has spineless, equal-sized and low dorsal fins, with the first dorsal fin being slightly closer to the pelvics than to its pectoral fins. The distance between the dorsal fin bases is about 70% of the distance from the snout to the first gill slits. It has a long lower caudal lobe and a short upper lobe, short caudal peduncle, and lateral keels variably present or absent on the base of the caudal fin.

A uniform greyish body and fins.

Adult females can reach 12.1 to 14.1 ft [3.7 to 4.3 m] in length. It is speculated that the species’ maximum length may be more than 23 ft [7 m], as estimated from photos.

The shark has spear-like upper teeth and slicing lower teeth with low bent cusps and high roots.

The shark prefers continental shelves and slopes, to depths of more than 6561.7 ft [2000 m]. They range into littoral in the north (once found trapped in a tide pool), and they go very deep in the south.

North Pacific from Japan to Mexico.


  • Prey – They feed on a wide variety of surface and bottom animals. Seal remains in their stomach may have been scavenged or taken alive.

  • Reproduction – They are probably ovoviviparous and have up to 300 large eggs per female.

These are lumbering and sluggish sharks. Their small mouth and large oral cavity suggest suction feeding. There is a possible sexual segregation (pregnant females not recorded).

Thought to be relatively common.