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Diet of Pacific sleeper shark, a potential Steller sea lion predator, in the north-east Pacific Ocean

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Pacific sleeper sharks Somniosus pacificus were captured near Steller sea lion Eumetopias jubatus rookeries during the period when Steller sea lion pups are most vulnerable to Pacific sleeper shark predation (first water entrance and weaning). Analysis of stomach contents revealed that teleosts were the dominant prey in August and cephalopods were the dominant prey in May (n = 198). Marine mammals were found in 15% of stomachs regardless of season, but no Steller sea lion tissues were detected. Molecular genetic analysis identified grey whale Eschrichtius robustus and harbour seal Phoca vitulina remains in some Pacific sleeper shark stomachs. Most mammals were cetacean and at least 70% of the cetaceans were probably scavenged. Although Pacific sleeper shark and Steller sea lion ranges overlapped, so predation could potentially occur, the diet study suggested that predation on Steller sea lions is unlikely, at least when pups first enter the water or during weaning. Harbour seals were infrequent prey and may have been consumed alive. Pacific sleeper sharks consume fast-swimming prey like Pacific salmon Oncorhynchus sp., most likely live animals rather than scavenged animals. Pacific sleeper sharks appeared to be opportunistic consumers of the available prey and carrion, feeding both on the bottom and in the water column, and their diet shifted to teleosts and cetacean carrion as the fish grew larger.
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Keywords: diet; predation; sea lion; sleeper shark

Document Type: Regular Paper

Affiliations: 1: Alaska Fisheries Science Center, Auke Bay Laboratory, National Marine Fisheries Service, NOAA, 11305 Glacier Highway, Juneau, Alaska 99801, U.S.A. 2: Bartlett Regional Hospital, 3260 Hospital Drive, Juneau, Alaska 99801, U.S.A. 3: Alaska Veterinary Pathology Services, P. O. Box 773072, Eagle River, Alaska 99577, U.S.A. 4: Southwest Fisheries Science Center, National Marine Fisheries Service, 8604 La Jolla Shores Drive, La Jolla, California 92037, U.S.A. 5: Institute of Marine Science, University of Alaska Fairbanks, P. O. Box 757220, Fairbanks, Alaska 99775, U.S.A.

Publication date: 2006-08-01

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