pacific sleeper shark

Large, deep-water Sleeper shark that ambushes and scavenges using mostly suction and tearing

The Pacific Sleeper shark (Somniosus pacificus) is a Sleeper shark of the family Somniosidae, found in the North Pacific on continental shelves and slopes in Arctic and temperate waters between latitudes 70°N and 22°N, from the surface to 6,600 feet deep. Its length is up to 14.1 feet, although it could possibly reach lengths of 23 feet or more.


Family: Somniosidae – Sleeper sharks

Genus: Somniosus 

Species: pacificus


Phylum– Chordata

Class– Chondrichthyles



Common NameDogfish Sharks

Family– Somniosidae

Common NameSleeper Sharks




Average Size and Length: On average, adult female Pacific Sleeper sharks are around 12 to 14.1 feet. The maximum recorded length is over 23 feet, based on video and photograph just outside Tokyo Bay in Japan.

Average Weight: On average, adult Pacific Sleeper sharks can weigh between 701 and 800 pounds. The largest recorded Pacific Sleeper shark weighed 1,958 pounds.

Current Rare Mythical Sightings:  Referenced above, the largest Pacific Sleeper shark was caught on film and photographed in deep water just outside Tokyo Bay in Japan in 1989. This shark was attracted to bait in the water. Eugenie Clark, a.k.a. The Shark Lady, made the length and weight estimations based on the footage.

In 2015 a pacific sleeper shark was filmed near the Solomon Islands underneath an active volcano. The shark is able to survive in water with a high temperature and acidity.

Teeth and Jaw: The Pacific Sleeper Shark has a very small mouth, with a very large oral cavity that is used for sucking prey into it. The upper teeth are spear-like for grabbing prey. The bottom teeth are ideal for slicing and tearing into prey. The cusps are bent and low, with high roots. The sleeper shark’s jaws are able to produce a powerful bite due to their short and transverse shape.

Head: The snout of the Pacific Sleeper shark is short and rounded.

Denticles: The skin of the Pacific Sleeper shark is rough and bristly. The dermal denticles have strong, hook-like erect cusps.

Tail: The lower caudal lobe is long and the upper caudal lobe is short. The caudal peduncle is short. The lateral keels on the bases are sometime present and sometimes not apparent. It is designed to allow the Pacific to store energy and engage in fast bursts to catch prey.

Demographic, Distribution, Habitat, Environment and Range: They are found in the North Pacific from Japan to Mexico. They can be found over continental shelves and slopes to over 6,600 feet. The Pacific Sleeper shark will range into the littoral north and very deep south. In the north, one was found trapped in a tide pool.

Diet: Research suggests that Pacific Sleeper sharks are both predators and scavengers. Only in Alaska has the shark’s diet been studied. Most of the 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 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. A 12.1-foot female shark found off Trinidad, California was found to have fed mostly on giant squid. Sleeper sharks found in Alaskan waters from 6.6 to 9.8 feet seem to feed mostly on flounder, pollock, and cephalopods, while sleeper sharks 10.8 to 13.9 feet long seem to eat mostly 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 (Markus Horning & Jo-Ann Mellish (2014). “In cold blood: evidence of Pacific sleeper shark (Somniosus pacificus) predation on Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska“).

Sleeper sharks are preyed on by the offshore ecotype of killer whales off British Columbia.

Ram-Suction Index: Pacific Sleeper sharks feed by means of suction and cutting of their prey. They have small mouths, but with very large oral cavities 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.

Aesthetic Identification: The Pacific Sleeper shark is a giant Sleeper shark with a uniform greyish body and fins. The body is heavy and cylindrical. They have small, precaudal fins. The dorsal fins are low, and are of equal size and do not have spines. The first dorsal fin is slightly closer to the pelvic fins then the pectoral fins. The distance between the dorsal fin bases is about 70% of the snout to the first gill slits.

Biology and Reproduction: They possibly segregate by sex (pregnant females are unknown). Research suggests that the Pacific Sleeper shark is ovoviviparous. They have up to 300 large eggs per female. The gestation time is unknown and litter sizes are thought to be about 10 pups. Its length at birth is about 1.38 feet or less.

Like the Greenland shark, the parasitic copepod Ommatokoita elongata can often be observed consuming the shark’s corneal tissue.

Since Pacific Sleeper sharks live in chilly depths, the liver oil does not contain squalene, which would solidify into a dense, nonbuoyant mass. Instead, the low-density compounds in the sharks’ liver are diacylglycerol ethers and triacylglycerol, which maintain their fluidity even at the lowest temperatures. They 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) in their tissues as osmoprotectants and to increase their buoyancy.

The Pacific Sleeper shark doesn’t always have the ability to feed when they need to; food is scarce. Therefore, the Pacific Sleeper shark stores food in its stomach.

Behavioral Traits, Sensing and Intelligence: The Pacific Sleeper shark is designed to be a stealth predator. They glide through the water with very little body movements and they make very little hydrodynamic noise. The Pacific Sleeper shark behaves in a lumbering and sluggish manner.

Speed: They glide through the water with very little body movement and very little hydrodynamic noise. They are extremely stealthy. Their caudal fin is designed to store energy and produce short, fasts bursts to capture fast-moving prey.

Pacific Sleeper Shark Future and Conservation: Unknown/Not Evaluated.

Pacific Sleeper Shark Recorded Attacks on Humans: Not a threat to humans.