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

Abstract

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 ¼ 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.

In cold blood: evidence of Pacific sleeper shark (Somniosus pacificus) predation on Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska

“…However, the attack behavior of the Pacific sleeper shark has not been studied. Pacific sleeper sharks do appear capable of preying on fast-swimming salmonids and scombrids (Ebert et al, 1987;Sigler et al, 2006). Larger and older Greenland sharks have been shown to prey on live pinnipeds (Fisk et al, 2002;Leclerc et al, 2012), although such events may be ambush attacks on seals sleeping at the ocean surface (Watanabe et al, 2012).…”

“…Pacific sleeper sharks have been documented in shallow coastal waters and even in estuarine waters in the arctic regions of the North Pacific and at oceanic depths (>2700 m) in temperate latitudes (Compagno, 1984;Ebert et al, 1987;Sigler et al, 2006;Yano et al, 2007). Although the very large (up to 7 m in total length [TL]) Greenland shark (Somniosus microcephalus) may have the northernmost range documented for species of this genus, the range of the Pacific sleeper shark extends into the Bering Sea and past the Arctic Circle (Bright, 1959;Orlov, 1999;Orlov andMoiseev, 1998, 1999;Benz et al, 2004;Hulbert et al, 2006;Courtney and Sigler, 2007).…”

“…Pacific sleeper sharks have a broad range of diet that includes benthic and mid-water crustaceans, cephalopods, salmonids, gadids, flatfish, and marine mammals (Bright, 1959;Compagno, 1984;Yang and Page, 1998;Orlov, 1999;Orlov andMoiseev, 1998, 1999;Sigler et al, 2006;Yano et al, 2007). Genetically identified stomach contents have included cetaceans and phocids; however, a histological analysis of ingested tissue indicated scavenging rather than live captures in the case of all cetacean and some phocid samples, and the evidence was inconclusive for some freshly ingested phocid tissue .…”

Predation on gray whales and prolonged feeding on submerged carcasses by transient killer whales at Unimak Island, Alaska

“…Yang & Page 1999). However, recent research by Hulbert et al (2006) shows that sleeper sharks make daily vertical movements and commonly ascend to depths of 100 m or less, particularly at night, and Sigler et al (2006) showed that the stomachs of sleeper sharks often contain marine mammal remains. We speculate that the frequent occurrence of gray whale carcasses in shallow water near Unimak Island attracts and provisions sleeper sharks every spring, resulting in greater concentrations of the species than in similar areas in the northeastern Pacific Ocean.…”

Habitat Use and Foraging Ecology of a Batoid Community in Shark Bay, Western Australia

“…Somniosus pacificus, increased size also results in the inclusion of marine mammals in the diet (Cliff et al 1989, Ebert 2002, Lucifora et al 2005, Sigler et al 2006). The aforementioned shifts are likely to at least in part be driven by smaller individuals being gape limited and too small to capture large prey.…”