Description & Behavior

Pacific sleeper sharks, Somniosus pacificus (Bigelow and Schroeder, 1944), are large deep-water sharks that reach about 4.4 m in length for males and 4.3 m for females. It is thought that this species can reach up to 7 m. The Pacific sleeper shark is dark gray to black with blue-black fins. The snout is short and rounded, the body is cylindrical, and the 2 dorsal fins are equal in size. The first dorsal fin is closer to the pelvic fins than the pectoral fins. Small precaudal fins are also present and the caudal fin (tail) is asymmetrical with a well-developed ventral (lower) lobe (?).

World Range & Habitat

Pacific sleeper sharks, Somniosus pacificus, can be found in temperate waters between 70°N-47°S in the North Pacific from Japan, along the Siberian coast to the Bering Sea and in southern California USA, Baja California, and Mexico. There are some sightings reported in the South Pacific. In Australasian waters, the Pacific sleeper shark is found from the seamounts south of Tasmania to the Challenger Plateau off eastern New Zealand, and possibly to Macquarie Island. In the southwest Atlantic they are seen off the coast of Uruguay.

This species prefers to inhabit continental shelves and slopes. At higher latitudes, the Pacific sleeper shark can be found in littoral (close to the shore) and even intertidal areas; in lower latitudes its depth ranges down to at least 2,000 m.

Feeding Behavior (Ecology)

Pacific sleeper sharks prey on bottom fishes, octopuses, squids (including giant squids and their even bigger relative, colossal squids), crabs and tritons; and occasionally harbor seals, steller sea lions and carrion.

Life History

Pacific sleeper sharks, Somniosus pacificus, are thought to be ovoviviparous. Pups measure about 42 cm or less.

Ovoviviparous: eggs are retained within the body of the female in a brood chamber where the embryo develops, receiving nourishment from a yolk sac. This is the method of reproduction for the “live-bearing” fishes where pups hatch from egg capsules inside the mother’s uterus and are born soon afterward. Also known as aplacental viviparous.

Conservation Status & Comments

Pacific sleeper sharks, Somniosus pacificus, are probably harmless to humans. The flesh of this species contains a toxin which can cause symptoms of intoxication.

References & Further Research

Arctic Science Journeys Radio: Sleeper Sharks Not So Sleepy
Antarctic jaws: cephalopod prey of sharks in Kerguelen waters, Deep Sea Research Part I: Oceanographic Research Papers, Volume 51, Issue 1, January 2004, Pages 17-31, Yves Cherel and Guy Duhamel
Primary photo above: Sleeper shark observed by ROV Tiburon at about 1076 meters depth on the Patton Escarpment, MBARI Seamounts Cruise, May 7, 2004

Research Somniosus pacificus @
Barcode of Life ~ BioOne ~ Biodiversity Heritage Library ~ CITES ~ Cornell Macaulay Library ~ Encyclopedia of Life (EOL) ~ ESA Online Journals ~ FishBase ~ Florida Museum of Natural History Ichthyology Department ~ GBIF ~ Google Scholar ~ ITIS ~ IUCN RedList (Threatened Status) ~ Marine Species Identification Portal ~ NCBI (PubMed, GenBank, etc.) ~ Ocean Biogeographic Information System ~ PLOS ~ SIRIS ~ Tree of Life Web Project ~ UNEP-WCMC Species Database ~ WoRMS

Search for Pacific Sleeper Sharks @
Flickr ~ Google ~ Picsearch ~ Wikipedia ~ YouTube