Pacific sleeper shark
|Pacific sleeper shark|
Bigelow & Schroeder, 1944
|Range of the Pacific sleeper shark|
The Pacific sleeper shark, Somniosus pacificus, is a sleeper shark of the family Somniosidae, found circumglobally on continental shelves and slopes in temperate waters between latitudes 70°N and 22°N, from the surface to 2,773 metres (9,098 ft). Its length is up to 4.4 m (14 ft), although FishBase accepts that it could possibly reach lengths in excess of 7 m (23 ft).
Pacific sleeper sharks, which are also known scavengers, can glide through the water with little body movement and little hydrodynamic noise making them successful predators. They feed by suction and cutting of their prey. They have large mouths that can inhale prey and their teeth cut up any pieces that are too large to swallow. They show a characteristic rolling motion of the head when feeding. Only in Alaska has the shark's diet been studied - most sharks' stomachs contain remains of giant Pacific octopus. They are also known to feed on bottom-dwelling teleost fishes as well as soles, flounders, Alaska pollock, rockfishes, shrimps, hermit crabs, and even marine snails. Larger Pacific sleeper sharks are also found to feed on fast swimming prey such as squids, Pacific salmon, and harbor porpoises. The diet of the Pacific sleeper shark seems to broaden as they increase in size. For example, a 3.7 m female shark found off Trinidad, California was found to have fed mostly on giant squid. Sleeper sharks found in Alaskan waters from 2 to 3 m (6.6 to 9.8 ft) seem to feed mostly on flounder, pollock, and cephalopods, while sleeper sharks 3.3 to 4.25 m (10.8 to 13.9 ft) long seem to consume teleosts and cephalopods, as well as marine mammals.
There is very little known about the early life of Pacific sleeper sharks. Pacific sleeper sharks are believed to produce eggs that hatch inside the female's body (reproduction is ovoviviparous), but gestation time is unknown and litter sizes are thought to be about 10 pups. Its length at birth is approximately 42 cm (1.38 ft) or less.
Pacific sleeper sharks are reported to reach lengths of up to 25 feet. The average mature size is 3.65 m (12.0 ft) and 318–363 kg (701–800 lb). The largest Pacific sleeper shark verified in size measured 4.4 m (14 ft) long and weighed 888 kg (1,958 lb), although FishBase accepts that it could possibly reach 7 m or more. In 1989, an enormous Pacific sleeper shark was attracted to a bait in deep water outside Tokyo Bay, Japan and filmed. The shark was estimated by Eugenie Clark to be about 7 m (23 ft) long.
Due to living in frigid depths, the sleeper shark's liver oil does not contain squalene, which would solidify into a dense, non-buoyant mass. Instead, the low-density compounds in the sharks' liver are diacylglyceryl ethers (DAGE) and triacylglycerol (TAG), which maintain their fluidity even at the lowest temperatures. Also, they store very little urea in their skin (like many deep sea sharks), but store high concentrations of trimethylamine oxide (a nitrogenous waste product). This helps the sleeper shark stabilize proteins that make up swimming muscles, digestive and reproductive hormones from the otherwise protein-denaturing effects of urea (Bennion and Dagget 2004). Because food is relatively scarce on the deep sea floor, the sleeper shark is able to store food in its capacious stomach. The sleeper shark's jaws are able to produce a powerful bite due to their short and transverse shape. The upper jaw teeth of the sleeper shark are spike-like, while the lower jaw teeth are oblique cusps and overlapping bases. This arrangement allows grasping and sawing of food too large to swallow. Pacific sleeper sharks have a short caudal fin, which allows them to store energy for fast and violent bursts of energy to catch prey.
Sleeper sharks are preyed on by the offshore eco-type of killer whales off British Columbia. In addition, like the Greenland shark, the parasticic copepod Ommatokoita elongata can often be observed consuming the shark's corneal tissue.
- D. A. Ebert, K. J. Goldman & A. M. Orlov (2008). "Somniosus pacificus". IUCN Red List of Threatened Species. Version 2009.2. International Union for Conservation of Nature. Retrieved February 6, 2010.
- Martin, R. Aidan. "Elasmo Research". ReefQuest. Retrieved 6 May 2009.
- Castro, José I., The Sharks of North America. Oxford University Press (2011), ISBN 978-0-19-539294-4
- Keven Drews, The Canadian Press. "Killer whales feast on sharks off B.C. coast". The Canadian Press. Retrieved 5 Sep 2011.
- General references
- "Somniosus pacificus". Integrated Taxonomic Information System. Retrieved 23 January 2006.
- Froese, Rainer and Pauly, Daniel, eds. (2005). "Somniosus pacificus" in FishBase. 09 2005 version.
- "New giant squid predator found". BBC News. 2004-01-08. Retrieved February 14, 2007.
- Castro, Jose. "Pacific Sleeper Sharks (Somniosus pacificus)." Conservation Science Institute. 1983. .
- Martin, R. A. "Pacific Sleeper Shark Bibliography." Biology of Sharks and Reys. ReefQuest Centre for Shark Research..
- "Megalodon caught on tape." My Paranormal Life. Google. . (Erroneously-labelled footage of a sleeper shark)
- Carroll, Amy. "Sleeper Sharks: Awake and Hungry Sleeper sharks Not Culprits in Sea Lion Declines." Alaska Fish and Wildlife News. 1999. Alaska Department of Fish and Game..
- Bennion, Brian J. and Valerie Daggett. (2004). Counteraction of urea-induced protein denaturation by trimethylamine N-oxide: A chemical chaperone at atomic resolution. Proceedings of the National Academy of Sciences of the United States of America. doi:10.1073/pnas.0308633101
- Paul Rincon (January 8, 2004). "New giant squid predator found". BBC News.
- ORCA Video of a sleeper shark