Pacific sleeper shark

The **Pacific sleeper shark** (*Somniosus pacificus*) is a species of Sleeper shark in the family Somniosidae that inhabits relatively deep Arctic and temperate waters between 22 and 70 degrees North. Some reports of Pacific sleeper sharks exist from southern oceans, however, these are most likely misidentifications, as some of its relatives are known to inhabit these waters, such as the southern sleeper shark (*Somniosus antarcticus*).

## Description

Aside from the Greenland shark (*Somniosus microcephalus*), the Pacific sleeper shark is typically regarded as being the largest member of the family Somniosidae, with some scientists even considering it to be larger than the Greenland shark. The largest verified individual measured 4.4 meters (14 feet) in length, and 888 kg (1,958 pounds). However, one individual attracted to a deepwater bait trap in Japan was estimated to be 7 meters long (23 feet) by shark expert Eugenie Clark. Although its size was not verified, it was filmed on camera, leading many to consider its size to be the maximum for the species.

Like the other species of Sleeper shark, the Pacific sleeper shark is dark grey to dark brown in color and has a fairly blunt nose along with a very small dorsal fin compared to its body size.

## Diet

The body design of the Pacific sleeper shark allows for minimized hydrodynamic noise, meaning that it is a very efficient ambush predator. One of their primary food sources appears to be cephalopods, as an examination of stomach contents revealed they feed on Giant Pacific Octopus as a primary food source. A 3.7-meter female found in California was found to have fed mostly on Giant squid. As these animals increase in size, their diet appears to grow. They seem to feed primarily on fish, cephalopods, crustaceans, and marine mammals. Because of the typical slow movement of Sleeper sharks, they are not assumed to be active predators, but rather hunt by ambush, as most of their prey seems to be able to easily escape them.

## Adaptations to Deep Sea Life

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. Also, 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. Trimethylamine oxide also serves to counteract the protein-destabilizing tendencies of urea and pressure. Its presence in the tissues of both elasmobranch and bony teleost fish has been found to increase with depth.

Because food is a relatively scarce resource on the deep sea floor, the sleeper shark is able to store food in its capacious stomach for long periods of time. The sleeper shark's jaws are also 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. When feeding, the shark rolls from side to side rather than shaking its head back and forth, allowing it to saw off large chunks of flesh with every bite. Pacific sleeper sharks have a short caudal fin, which allows them to store energy for fast and violent bursts of energy to catch prey.

In 2015 a pacific sleeper shark was filmed near the Solomon islands underneath an active volcano. Based on this and other discoveries, the shark is able to survive in water with a high temperature and acidity in addition to the cold waters it usually inhabits.

## Enemies

Off of British Columbia, Pacific Sleeper sharks are targeted as food by killer whales (*Orcinus orca*), and often fall victim to a similar parasite to those found feeding on the corneal tissue of the Greenland shark in the Atlantic: the parasitic copepod *Ommatokoita elongata.*

## In Popular Culture

Pacific sleeper sharks have been filmed in a few notable documentaries. Two Shark Week documentaries, Alien Sharks, and Big Tooth: Dead or Alive? have shown footage of them, with the latter showing footage of the giant 23-foot specimen filmed off Japan. This same footage was used in the National Geographic special "Sea Monsters: Search for the Giant Squid".