- Linda Weiss
March Elasmobranch of the Month: Pacific Sleeper Shark
Pacific Sleeper Shark
The Pacific Sleeper shark is a large species, with an average length between 3.7 – 4.3 m (12.1 -14.1 ft). Based on video and photographs, a maximum length recorded was approximately 7 m (23 feet). The heaviest recorded Pacific Sleeper shark weighed 888kg (1,958 pounds). Average weight is between 317.5 – 362.9 kg (700-800 pounds). They are a heady-bodied, cylindrical shark. They have a short and rounded snout. Their fins are relatively small for their body size and rounded. Their first and second dorsal fins are of equal size. The caudal fin is broad and paddle-shaped, not having a distinct fork between the upper and lower lobes. Its body coloration is uniformly dark gray to black. This shark’s mouth is small. The teeth of the upper jaw are spear-shaped while the teeth in the lower jaw are short with tilted cusps.
Habitat and Distribution
The Pacific Sleeper shark is a deep-water species found in the Pacific Ocean from Japan to Baja California, Mexico and the Hawaiian Islands. This shark inhabits continental shelf areas and slopes at depths down to 2008 m (6,590 feet).
The Pacific sleeper’s diet is fairly diverse, including squid, octopuses, fishes, crab, mollusks, shrimp, sea lions and porpoise.
This shark species reproduces ovoviviparously. Yolk-sacs provide nourishment to the embryos inside eggs inside the female until they are ready hatch inside her to be birthed alive. Gestation time is not known. Litter size is estimated at 10 pups. The newborns measure 40 - 65 cm (16 -25.6 inches) long.
The IUCN Red List of Threatened Species currently lists the Pacific sleeper shark as Near Threatened, with a decreasing population trend.
Humans pose the biggest threat to this species. They are discarded bycatch in the commercial fishing industry, caught by trawls and longlines. One known natural predator is the orca.
Planet Shark Divers
Shark Research Institute
Ebert, D.A., Goldman, K.J. & Orlov, A.M. 2009. Somniosus pacificus. The IUCN Red List of Threatened Species 2009: e.T161403A5416294. https://dx.doi.org/10.2305/IUCN.UK.2009-2.RLTS.T161403A5416294.en. Accessed on 12 March 2023.