Pacific sleeper shark

The Pacific sleeper shark (Somniosus pacificus) is a very large shark of the family Somniosidae; the sleeper sharks. It is found in the Pacific Ocean as per its scientific and common names, once thought to be restricted to the Northern Hemisphere, but have subsequently been proven to be present in the Southern Hemisphere.

Pacific sleeper shark
Conservation status
Near Threatened  (IUCN 3.1)[1]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Elasmobranchii
Division:	Selachii
Order:	Squaliformes
Family:	Somniosidae
Genus:	Somniosus
Species:	S. pacificus
Binomial name
Somniosus pacificus Bigelow & Schroeder, 1944
Range of the Pacific sleeper shark

Description

The average mature size of this species 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 it could possibly reach 7 m (23 ft) or more;^[2][3] an enormous Pacific sleeper shark was attracted to a bait in deep water outside Tokyo Bay, Japan, and filmed in 1989. The shark was estimated by Eugenie Clark to be about 7 m (23 ft) long.^[4] A single unconfirmed account exists of an enormous Pacific sleeper shark that potentially measured more than 9.2 m (30 ft) long.^[5] If true, this would make the species the largest extant macro-predatory shark, and the third largest shark overall after the whale shark and the basking shark.

Similar to the Greenland shark, the parasitic copepod Ommatokoita elongata can often be observed consuming the shark's corneal tissue, which degrades their eyesight.^[6]

Adaptations

Due to living in frigid depths, the sleeper shark's liver oil does not contain squalene, which would solidify into a dense, nonbuoyant mass. Instead, the low-density compounds in the sharks' liver are diacylglyceryl ethers and triacylglycerol, which maintain their fluidity even at the lowest temperatures. They also store very little urea in their skin (like many deep sea sharks), but like other elasmobranchs, have high concentrations of urea and trimethylamine oxide (nitrogenous waste products) within their tissues as osmoprotectants and to increase their buoyancy.^[7] Trimethylamine oxide also serves to counteract the protein-destabilizing tendencies of urea^[8] and pressure.^[9] Its presence in the tissues of both elasmobranch and teleost fish has been found to increase with depth.^[9][10]

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 comprise of 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.^{[4][better source needed]}

Distribution

The Pacific sleeper shark is found in the North Pacific on continental shelves and slopes in Arctic and temperate waters between latitudes 70°N and 22°N and in at least two places in the western tropical Pacific near Palau and the Solomon Islands, from the surface to 2,000 metres (6,600 ft) deep.^[1][2] The first evidence of the sharks in the western tropical Pacific emerged from a National Geographic video taken near the Solomon Islands in 2015.^[11]

In 2015 a Pacific sleeper shark was filmed near the Solomon Islands underneath an active volcano.^{[12][better source needed][13]} This species has also been recorded in the Tonga Trench, filmed in 2024.^[14]

Biology

Trophic ecology

Pacific sleeper sharks are thought to be both predators and scavengers. They can glide through the water with little body movement and little hydrodynamic noise, making them successful stealth predators.^{[citation needed]} They feed by means of suction and cutting of their prey, possessing large mouths that can essentially inhale prey, with their teeth cut up any pieces that are too large to swallow.^{[citation needed]} They show a characteristic rolling motion of the head when feeding. Since they lack a nictitating membrane that other sharks have, they roll their eyes back in their sockets to protect them from thrashing prey.^[15]

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.^{[citation needed]} 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. A recent study in the Gulf of Alaska suggests that sleeper sharks may prey on juvenile Steller sea lions.^[16] Alaskan populations often feed on the giant Pacific octopus. These are also known to feed on bottom-dwelling fish, such as soles, flounders, Alaska pollock, rockfishes, along with shrimps, hermit crabs, and even marine snails.^[17] Larger Pacific sleeper sharks are also found to feed on fast-swimming prey, such as squids, Pacific salmon, and harbor porpoises.^[18]

Sleeper sharks are preyed on by the offshore ecotype of killer whale off British Columbia.^[19]

Reproduction

Very little is known about the early life of Pacific sleeper sharks. They are believed to produce eggs that hatch inside the female's body (being ovoviviparous), but gestation time is unknown and litter sizes are thought to be about 10 pups. Its length at birth is about 42 cm (1.38 ft) or less.^{[4][better source needed]}

See also

• Sharks portal

• Greenland shark
• List of sharks