Tuesday, October 18, 2011

Pacific Sleeper Shark

The Pacific Sleeper Shark has been most extensively studied in the Gulf of Alaska. Here, 73% of Pacific Sleeper stomachs examined contained remains (principally the horny, parrot-like beaks) of the Giant Pacific Octopus (Enteroctopus dofleini). Alaskan Pacific Sleepers also prey heavily on bottom-dwelling teleost fishes — including a variety of soles, flounders, pollocks and rockfishes — but also take fast swimming prey — such as squids (Loligo, Ommastrephes, and others), Pacific salmon (Oncorhynchus spp.), and Harbor Porpoise (Phocoena phocoena) — as well as crunchy bottom-dwelling invertebrates — such as shrimps, hermit crabs, and even marine snails (including large, heavily-shelled tritons of the genus Fusitriton).

Like that of the White Shark (Carcharodon carcharias), the diet of Pacific Sleeper Sharks seems to broaden as they increase in size. A 3.7-foot (1.1-metre) female specimen from off Trinidad, California, was found to have fed mostly on Pacific Giant Squid (Moroteuthis robustus). The sharks included in the Gulf of Alaska study cited above ranged in length from 6.5 to 10 feet (2 to 3 metres) and had fed mostly on flounder, pollock, and cephalopods. Larger Pacific Sleepers, between 11 and 14 feet (3.6 and 4.3 metres) in length consume not only teleosts and cephalopods, but also marine mammals. A 13.5-foot (4.2-metre) male specimen captured off Patagonia contained three, 3-foot (1-metre) long Patagonian Toothfish (Dissostichius eleginoides) and numerous squid beaks. A 12-foot (3.6-metre) female Pacific Sleeper caught off the coast of Chile had in its stomach a whole, 34-inch (87-centimetre) Southern Rightwhale Dolphin (Lissodelphis peronii), while the 11-foot (3.9-metre) female that was stranded and shot in Kachemak Bay, Alaska, contained three octopuses, complete and shattered Tanner Crabs (Chionectes bardi), fragments of Hairy Tritons (Fusitriton oreganensis), and portions of at least three Harbor Seals (Phoca vitulina).

Interestingly, although they often live near haul-outs of Steller’s Sea Lions (Eumetopias jubatus) and have the dentition to ‘process’ them, Pacific Sleeper Sharks in the Gulf of Alaska are not known to feed upon these large, calorie-rich pinnipeds. However, like any card-carrying shark, the Pacific Sleeper is ever ready to scavenge whenever the opportunity arises. And the annual 13,000-mile (21,000-kilometre) round-trip migration of the Grey Whale (Eschrichtius robustus) along the Pacific Coast of North America — from winter feeding grounds in the Gulf of Alaska to summer calving lagoons in the Sea of Cortez — provides ample opportunities, as many participants cannot endure the arduous journey.

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