Pacific Sleeper Shark

Pacific Sleeper Sharks are most commonly found in the North Pacific, on continental shelves and slopes, in Arctic and temperate waters. These sharks can be found between latitudes of 70 degrees north and 22 degrees north, and from the surface to 6,600 ft (2,000 meters) deep. Any records that place them in the southern oceans are likely misidentifications of the sharks’ relatives.

Pacific Sleeper Shark Facts

• It is possible for a Pacific Sleeper Shark to grow up to 23 ft in length!
• Pacific Sleeper Sharks can glide through the water with little body movement and very little noise.
• Their large mouths allow them to easily inhale prey.
• They show a characteristic rolling motion of the head while feeding.
• The Pacific Sleeper Shark’s diet appears to broaden as they increase in size.

Classification and Scientific Name

The scientific name for the Pacific Sleeper Shark is Somniosus pacificus. The genus Somniosus is a widely distributed genus that consists of several members that rank among the largest of sharks.

It is classified as Chondrichthyes, which derives from Ancient Greek (khóndros) ‘cartilage’ and (ikhthús) ‘fish’. It is a class that contains cartilaginous fishes that have skeletons that are primarily composed of cartilage.

Identification and Appearance

Pacific Sleeper Sharks are large deepwater fish that reach an average of 4.4 m (14 ft) in length for males and 4.3 m (14.1 ft) for females. It is said that some of the largest fish in this species can reach lengths of up to 7 m (23 ft). It is dark grey to black in color, and it has blue-black fins. The snout of the shark is short and rounded, while the body is cylindrical. Its two dorsal fins are equal in size, while the first dorsal fin is closer to the pelvic fins than the pectoral fins. It has small precaudal fins that are also present, and its caudal fin (tail) is asymmetrical with a well-developed ventral (lower) lobe.

Habitat and Feeding Patterns

Pacific Sleeper Sharks are thought to be both predators and scavengers. They can glide through water using little body movement and making little hydrodynamic noise. This makes them very successful stealth predators. They feed by a means of suction and by cutting their prey with their teeth. The Pacific Sleeper shark has a large mouth that can essentially inhale all of its prey as it swims through the water. As they take in their prey, they cut up any pieces that are too large to swallow with their sharp teeth. They also display a characteristic rolling motion of their head while feeding.

The Pacific Sleeper Shark’s diet has only been studied in Alaska. The studies showed that most of the sharks’ stomachs contained the remains of giant Pacific octopuses. They are also known to feed on bottom-dwelling teleost fishes as well as soles, Alaskan pollock, flounders, shrimps, hermit crabs, marine snails, and rockfish.

Larger Pacific Sleeper sharks have also been found to feed on fast-swimming prey such as Pacific salmon, squids, and harbor porpoises. The diet of the Pacific Sleeper Shark appears to broaden as the size of the shark increases. As an example, there was a 12.1-foot (3.7-meter) female shark that was found off the coast of Trinidad, California, which was found to have mostly fed on giant squid as its main food source. Sleeper sharks that were found in Alaskan waters that were from 2 to 3 meters (6.6 to 9.8 ft) seem to have mostly fed on flounder, pollock, and cephalopods.

Conservation

The Pacific Sleeper Shark is a large, deep-water shark that is slow to mature and reproduce. Because of this, the sharks’ populations can be particularly vulnerable to the effects of being caught and released with fishing gear. This makes conservation efforts for the shark an important factor. The key objective of many conservation efforts is to capture, tag, and release the Pacific Sleeper Sharks in order to study their movements, behavior, and habitat preferences off Southern California. The information that is produced by these studies will be used to help advance the current scientific knowledge that is available on Pacific Sleeper Sharks. According to the IUCN Red List, the Pacific Sleeper Shark is currently classified as Near Threatened due to bycatch in fisheries and its slow reproductive rate.

Predators

Pacific Sleeper sharks have been preyed on by killer whales. Orcas were spotted off the coast of British Columbia feasting on Pacific Sleeper Sharks. Orcas mainly congregate on the edge of the continental shelf, and while it is known that many killer whales feed on salmon and other fish, and transient orcas focus almost exclusively on marine mammals, the diets of offshore killer whales have generally stumped researchers — until recently.

The researchers began to hypothesize that the whales were targeting the sharks after they observed worn-down teeth on some of the orcas that had become stranded. This was finally confirmed when a group of them was spotted feeding south of Alaska. After a few minutes passed, chunks of tissue and oil could be seen floating to the surface. They were later examined and proven to be parts of the liver from Pacific Sleeper Sharks. It was later said that the orcas were believed to have been going after the sharks because they were the most ‘profitable’ prey, containing the biggest body sizes and oil content, which they needed to eat as a source of fuel and energy.

Reproduction

There is very little information known about the early life of Pacific Sleeper Sharks. They are believed to produce eggs that are hatched inside the female shark’s body (the reproduction is ovoviviparous). The gestation time is unknown, and the average litter size is thought to be about 10 pups. The shark’s length at birth is about 42 cm (1.38 ft) or less.

Adaptations

Since these sharks live in the frigid depths of the water, the sleeper shark’s liver oil does not contain squalene, which would normally solidify into a dense, non-buoyant mass. The low-density compounds of the sharks’ liver help maintain their fluidity, even at the lowest temperatures.

Because food can be relatively scarce on the depths of the ocean floor, the Pacific Sleeper Shark is able to store food in its capacious stomach. Their jaws are also able to produce a powerful bite because of their short and transverse shape. The upper jaw of one of these sharks is spiked, while the lower one has a few oblique cusps and overlapping bases. This arrangement allows them to grasp and saw at their food as they inhale it while swimming. The sharp teeth at the top allow it to cut its food into smaller, more manageable pieces as it goes in. They also have a short caudal fin, which allows them to store their energy for fast, violent bursts of energy that they need to capture prey.

Even though these sharks are most commonly found deep in the ocean, where the temperature can be quite cold, a Pacific Sleeper Shark was found near the Solomon Islands in 2015, underneath an active volcano! This shows that the shark is very adaptive and is able to survive in water that has very high temperatures and acidity levels.