Pacific sleeper sharks are designed for stealth. Their eyesight is probably poor, but good eyesight is not necessary since they have an exceptional “sixth sense" to detect very slight electromagnetic fields. Muscle activity, even the beating of an animal’s heart or the movement of its diaphragm, emits an electrical signal that the sharks use to detect, locate and attack their victims. Under cover of darkness prey would be less likely to detect a sleeper shark coming up from the depths. Prey emits electromagnetic signals that guide the shark right in. For sleeper sharks, darkness is not a deterrent to detecting prey, but instead a cover or camouflage.
Pacific sleeper shark teeth are quite different in the lower jaw compared to the upper jaw. The upper jaw has small, sharp, conical teeth much like those in halibut. These are used to seize and hold prey. The teeth in the lower jaw are interlocking, forming a serrated blade used for slicing. Sleeper shark bite marks resemble large three-quarter moons or slices.
Sleeper sharks attack suddenly and without warning. A harbor seal might be floating on the surface of the ocean trying to catch its breath when it is attacked from below by a 400-pound (181-kg) sleeper shark. A bite to its midsection and the seal is eviscerated and struggling for its life. At minimum, the shark gets a large chunk of skin and blubber, likely enough to cause the seal soon to die. However the shark will finish the job by ripping the seal to bits, eating and digesting the entire animal. Smaller animals such as adult chum salmon or black cod usually are eaten whole.
Halibut and black cod struggling on a fisherman’s long line (bottom-set line with hundreds of baited hooks) attract sleeper sharks. The struggling fish emit signals that the sharks can detect from long distances. The sleeper sharks bite chunks out of the halibut. When sharks try to eat the cod whole, the same hook that caught the cod may hook the sharks. The struggling sleeper sharks tangle and damage commercial fishing gear, forcing many fishermen to change fishing areas.
CURRENT STATUS: Pacific sleeper shark numbers increased dramatically in the North Pacific during the 1980s and 1990s. In areas where few sharks ever were caught before, now fishermen are catching many more sleeper sharks. Many fishermen are reporting more and larger sharks each year in the Gulf of Alaska.
ECOLOGY/CONSERVATION: During the 1970s, temperatures in the North Pacific Ocean increased, followed by a change in species composition in the region. The ecosystem supported great quantities of shrimp and crab before the 1970s, but these species nearly disappeared and were replaced by pollock, cod, halibut and arrowtooth flounder. This species composition change is referred to as a “regime shift.” Other noteworthy and dramatic changes included decreases in sea lions, seals and forage fish (capelin, sandlance and herring) and increases in salmon sharks and Pacific sleeper sharks.
One theory explaining the regime shift involves increased winds, global warming, the Gobi Desert, iron and a group of phytoplankton (small single-celled plants) called “diatoms.” As the Earth warms due to global warming, scientists predicted, and have seen, stronger and more persistent winds. When these winds are especially strong they can sweep across the Gobi Desert of Mongolia carrying tons of dust laden with the element iron. Much of this iron is deposited in the North Pacific Ocean, which promotes the growth of a class of organisms called diatoms. Diatoms are single celled plants and can grow rapidly if the conditions are right. The diatoms use iron in a process that keeps them near the water’s surface and in the euphotic zone where they capture the sun’s energy. When the iron supply is used up, the diatoms sink to the bottom of the ocean. If there is lots of iron and it comes in a steady supply, the diatom population blooms and diatoms stay near the surface of the ocean and promote the surface food web and ecosystem. But if the winds are sporadic the diatoms grow, but soon deplete the iron in the water and sink to the bottom. This may be better for the ocean floor food web and ecosystem. The regime shift of the late 1970s may have been a result of the processes described here. As global warming changes wind patterns and the strength of the wind, we can expect more regime shifts and ones of greater magnitude.
Another theory of reduced marine mammal populations is that great white sharks have become abundant in Alaskan waters. Sharks are secretive by nature and do not readily reveal their presence, making it difficult for scientists to study. Sleeper shark populations are at record highs in the North Pacific, and they are preying on many species of fish and on some marine mammals. Sharks may be exerting an influence on the North Pacific marine ecosystem that will be long-lasting. Some scientists and many fishermen are concerned about what will happen, now that sharks are so common in the North Pacific Ocean. Many people have proposed shark predator-control programs without understanding the consequences.
Mathematical ecosystem models predict that there may be worse consequences if people reduce the shark population than there will be if they do not. Though sharks compete for some of the fish people catch and eat, sharks also reduce large changes in prey population numbers. According to some population models, removing sharks likely will result in increased salmon, black cod and pollock numbers. The increase in these smaller predatory fish would increase predation on smaller but extremely important forage fish such as herring, capelin and sandlance. The predicted outcome of the subsequent declines of the forage fish is for further reductions of seal and sea lion populations. This would be bad for fishermen. It also would be a big concern for those people trying to bring the sea lion back from the brink of extinction.
The Pacific sleeper shark (Somniosus pacificus) is a secretive, deep-dwelling shark referred to by many fishermen as the “mud shark.” The Greenland shark is found in the North Atlantic Ocean and is a similar species.
Pacific sleeper sharks have been caught that exceed 20 feet (6 m) in length, which would weigh in at about 8000 pounds (3600 kg). This is approaching the size of adult orcas.
Pacific sleeper sharks probably live more than 40 years. This age estimate is based upon the size this species obtains and upon the average growth rates. Determining the age of sharks is problematic. Bony fish can be aged by counting the annual rings on a bone in the ear called an otolith; most sharks do not have any bones and no shark has an otolith.
Deep underwater video has captured many Pacific sleeper sharks feeding together on whale carcasses. The sharks appear to be non-aggressive towards each other as they feed. No information is available on other sleeper shark social interactions.
Pacific sleeper sharks are found in polar and sub-polar waters throughout the year. They occur in the Pacific Ocean from Baja California north to the Bering Sea, Chukchi Sea, Beaufort Sea, and to the Okhotsk Sea off of Japan. They inhabit cold, deep waters to depths exceeding 6500 feet (1981 m). At higher latitudes sleeper sharks use shallow as well as deep waters.
Satellite tags have been attached to Pacific sleeper sharks to determine their movements. Tag data indicates that individual sharks moved from the bottom, 2000 feet (610 m) deep, to the surface each night, apparently to feed. The limited tag data indicate that they did not migrate to other areas.
Pacific sleeper shark tissue is reported to be toxic to people and other animals. They are probably only preyed upon by other sharks. Commercial fishermen regularly kill Pacific sleeper sharks that they catch while fishing for black cod and halibut.
The species associated with this article are major components of the successionary communities arising around bathyal whale carcasses (though by no means the only whale-fall associated species).
A whale carcass arriving on the bathyal sea-floor (roughly 700-1000m depth) represents a massive influx of nutrients to an otherwise nutrient-poor ecosystem (Lundsten et al 2010a; Lundsten et al 2010b; Smith and Baco 2003). The background rate of carbon deposition to the deep-sea floor is on the order of tens of kilograms per hectare per year (Smith and Baco 2003); an adult whale can weigh up to 160 tons. Consequently, it has long been thought that whale carcasses must represent a significant source of nutrients for sea-bed communities. Additionally, since the discovery of deep-sea hydrothermal vents and cold seeps, it has been hypothesized that whale-falls may serve as stepping stones for the dispersal of organisms between chemosynthesis-dominated bottom communities (Smith and Baco 2003).
The community observed to spring up around whale carcasses has been characterized as having three major successionary stages (Danise et al 2012):
-Mobile scavenger stage: large, mobile detritivores consume the flesh of the whale.
-Enrichment opportunist stage: slow-moving or sessile organisms colonize the nutrient-enriched area in and around the carcass.
-Sulphophilic stage: a chemosynthesis-dominated system based on the sulfides released by anaerobic decomposition of bone lipids.
The duration of the first stage depends largely on the mass of the whale, ranging from a few months to up to one and a half years. Initially the community is dominated by large detritivores such as sleeper sharks and hagfish, but as the amount of flesh available decreases, smaller scavengers such as rattails, amphipods, and and lithodid crabs begin to replace them. Once the bulk of the tissue is removed from the skeleton, the community begins to shift to phase two. At this point, extremely dense populations of dorvilleid worms and other polychaetes, as well as crustaceans and gastropods colonize the area around the carcass, exploiting the rich organic material in the surrounding sediments. The rapid recruitment of these organisms suggests they may be opportunistic whale-fall specialists. Over time, without a discrete boundary, sulphide emission from anaerobic decay of bone lipids in the whale skeleton begins to support a chemosynthetic fauna similar to that found around cold seeps and hydrothermal vents, including bacteria, organisms with endosymbiotic bacteria, bacterial grazers, and small predators. This community may linger for up to several decades (Smith and Baco 2003). Fossil evidence suggests that a similar pattern of succession has been evolving since the late Miocene, and may even have operated on the carcasses of Cretaceous plesiosaurs (Danise et al 2012).
As always in ecology, this picture is somewhat oversimplified. In two 2010 articles, Lundsten et al observe that in addition to chemosynthetic fauna and whale-fall specialists, whale carcasses are often characterized by increased density of the background sea-floor organisms, particularly as time passes since the fall of the whale. Lundsten et al and Glover (2010) additionally found that there is a notable depth gradient in community structure, with fully sulphophilic ecosystems only developing on large, deep carcasses.
The function of whale-falls as stepping stones between cold seeps and hydrothermal vents remains unproven, but there is evidence for relatively large numbers of whale-fall specialist species, especially in the enrichment opportunist and sulphophilic stages (Smith and Baco 2003). Nearest-neighbor analyses of whale falls based on whale populations and the probability of a carcass sinking suggest that carcasses are distributed such that most organisms found in the latter two stages could easily disperse larvae between whale-fall sites. Unfortunately, this ecosystem may be endangered by declining whale populations and may even have already lost a great deal of diversity, as 19th century whale-fall density was likely up to six times higher than that in the present day (Smith and Baco 2003).
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 2,000 metres (6,600 ft) deep.[1][2] Records from southern oceans are likely misidentifications of relatives.[1] Its length is up to 4.4 m (14 ft), although it could possibly reach lengths in excess of 7 m (23 ft).[2]
Pacific sleeper sharks, which are thought to be both predators and scavengers, can glide through the water with little body movement and little hydrodynamic noise, making them successful stealth predators. They feed by means of suction and cutting of their prey. They have large mouths that can essentially 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. Only in Alaska has the shark's diet been studied - most 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 even 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. For example, a 3.7-m female shark found off Trinidad, California was found to have fed mostly on giant squid. 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.[3]
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 (reproduction is 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]
The average mature size 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][5] In 1989, an enormous Pacific sleeper shark was attracted to a bait in deep water outside Tokyo Bay, Japan, and filmed. 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 [6]. 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.
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.[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 are 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]
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.[11][12]
Sleeper sharks are preyed on by the offshore ecotype of killer whale off British Columbia.[13] In addition, like the Greenland shark, the parasitic copepod Ommatokoita elongata can often be observed consuming the shark's corneal tissue.
Pacific sleeper shark carcasses 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 2,000 metres (6,600 ft) deep. Records from southern oceans are likely misidentifications of relatives. Its length is up to 4.4 m (14 ft), although it could possibly reach lengths in excess of 7 m (23 ft).
