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    Sleeper Shark

    SleeperShark

    Pacific sleeper shark recently captured by John W. Melovidov and Charles Stepetin on Sept. 3, 2015 near St. Paul Island.

    The Pacific sleeper shark (Somniosus pacificus) recently captured and posted by John W. Melovidov and Charles Stepetin on Sept. 3, 2015 near St. Paul Island is the most abundantly caught shark in the Bering Sea surveys. Two additional sharks that are abundant in Alaskan waters are spiny dogfish (Squalus suckleyi) and salmon shark (Lamna ditropis). Although there is no current directed fishing for these species, they are often caught incidentally. Little is known about these sharks’ life histories in Alaska, but research on their ages, natural mortality, movements, diets, and maturity is ongoing. (See http://www.afsc.noaa.gov/ABL/MESA/mesa_sa_sharks.php).

    Details of the sleeper shark’s range and population status are somewhat sketchy but they can be found as far north as the Arctic Circle in the Chukchi Sea, off the Asian and Russian coasts to the west, and as far south as California. Whether they are moving north with increasing temperatures is unknown. They are commonly called mud sharks because they are found at the bottom of the ocean, up to 6500 feet (2000 m) deep! They are known to largely feed on bottom dwelling prey such as arrowtooth flounder and giant octopus. Their large eyes suggest the ability to effectively collect light in the deep dark abyss. Their large snout nose is thought to serve as an effective means of following the chemical trails (smell) of decomposing flesh on the bottom of the ocean. Sleeper sharks can also glide through the water with very little body movement and minimal noise, and often appear to be continuously changing depths at incredible rates (6 km/day; Hulbert et. al., 2006).

    Their ability to capture fast-swimming prey such as salmon, squid and tuna, combined with their abundance in areas around pinniped breeding colonies, has led some scientists to hypothesize that they may have played a role in the population decline of Steller sea lions. There is indirect evidence of these sharks eating Steller sea lions; a temperature sensor on a Steller sea lion that began recording the low temperatures expected in a sleeper shark’s stomach after the sea lion was presumably preyed upon (Horning et al. 2013). Tracking and diet studies have not supported this idea but have confirmed that sleeper sharks could forage on other marine mammals such as harbor seals (Sigler et al. 2006). This is not hard to believe given their excellent swimming abilities combined with their large size, commonly reaching 14 feet (4 m) and sometimes as large as 23 feet (7 m) in length. All of these traits appear to have made them very successful predators.

    Sleeper sharks do not have a history of being harmful to humans. Their sluggish and quiet behavior in boats when captured makes it hard to believe they are closely related to the aggressive Greenland shark. That said, keeping hands away from their small mouth, which is designed for suction and for cutting meat, would be a good rule of thumb! Fishermen could provide important information to understand more about these animals by taking and posting photos (and letting us know!) when they are incidentally caught.

    Horning, M. and J. E. Mellish. 2013. In cold blood: evidence of Pacific sleeper shark (Somniosus pacificus) predation on Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska. Fish. Bull. 112:297–310.

    Hulbert, L. B., M. F. Sigler, and C. R. Lunsford. 2006. Depth and movement behavior of the Pacific sleeper shark in the north-east Pacific Ocean. J. Fish Biol. 69:406–425.

    Sigler, M. F., L. B. Hulbert, C. R. Lunsford, N. H. Thompson, K. Burek, G. O’Corry-Crowe, and A. C. Hirons. 2006. Diet of Pacific sleeper shark, a potential Steller sea lion predator, in the north-east Pacific Ocean. J. Fish Biol. 69:392–405.

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