406 



Diet of Pacific sleeper shark, 



Somniosus pacificus, In the Gulf of Alaska 



Mei-Sun Yang 



Benjamin N. Page 



Alaska Fisheries Science Center 

 7600 Sand Point Way NE 

 Seattle, Washington 98115-0070 



E-mail addre5s Mei-Sun Yangffnoaa gov 



The sleeper shark, Somniosus paci- 

 ficus, ranges from Chile (Crovetto 

 et al., 1992 ) through southern Cali- 

 fornia (Phillips, 1953), British 

 Columbia to the Gulf of Alaska 

 (Bright, 1959), the Bering Sea 

 (Wilimovsky,1954), and Japan 

 (Tanaka et al.,1982). It is thought 

 to be a voracious and versatile 

 feeder and its diet has been shown 

 to include young marine mammals, 

 such as harbor seal, Phoca vitulina 

 (Bright, 1959), and the southern 

 right whale dolphin, Lissodelphis 

 peronii, (Crovetto et al.,1992). The 

 purpose of this study is to describe 

 the diet of the sleeper shark in the 

 Gulf of Alaska area. 



Methods 



Sleeper sharks were collected in the 

 Gulf of Alaska (Fig. 1) between 

 June and August 1996 from the 

 longline vessel A/as/?a Leader, and 

 the bottom-trawl vessels Vester- 

 aalen and American No. 1. After 

 dissections onboard, each indi- 

 vidual stomach was put in a plas- 

 tic bag and frozen at sea. Tags re- 

 cording date, location, and length 

 and sex of shark were included in 

 the sample bag. Information on the 

 station, shark total length (TL) 

 (measurements follow Castro, 

 1983), and dates samples were col- 

 lected are listed in Table 1. Stom- 

 achs were thawed in the laboratory 

 and stomach contents were ana- 

 lyzed. Prey were identified to the 



lowest taxonomic level possible. 

 Each prey item was weighed and 

 standard length of prey fish was 

 measured. Percent frequency of oc- 

 currence and the percentage of the 

 total weight of each prey item were 

 calculated. Octopus beak measure- 

 ments were made to estimate live 

 wet weights of octopi. According to 

 Robinson and Hartwick ( 1983), pig- 

 ment-upper-lateral-wall length 

 (PULWL) has the best correlation 

 coefficient with the live wet weight 

 of the North Pacific giant octopus. 

 Octopus dofleini; we therefore used 

 these PULWLs to estimate the live 

 wet weight of the octopus. Live wet 

 weights of Octopus dofleini that 

 had been consumed were calculated 

 by using Robinson and Hartwick's 

 (1983) equation: 



In (PULWUmm)) 



= 0.274 In {weight(\ig) 



-(-2.674. 



(1) 



Results 



A total of 13 sleeper shark stomachs 

 were analyzed; two were empty, 11 

 contained food (Tables 1 and 2). The 

 length of the sleeper sharks ranged 

 from 218 cm to 295 cm TL (mean= 

 264.5 cm; SD=24.9 cm. Arrowtooth 

 flounder, Atheresthes stomias, was 

 the most important prey, represent- 

 ing &!'/( of the total stomach con- 

 tent weight (64*^ of frequency of 

 occurrence). The size of arrowtooth 

 flounder consumed by sleeper 



sharks ranged from 38 cm to 65 cm 

 TL, (mean=44.8 cm; SD=8.0 cm). 

 Other prey included a 48-cm wall- 

 eye pollock, Theragra chalcogram- 

 ma (5.2% by weight), a single 33- 

 cm rockfish, Sebastes sp., a 40-cm 

 Pacific salmon, Oncorhynchus sp., 

 and a 26-cm flathead sole, Hippo- 

 glossoides elassodon, as well as 

 three unidentifiable flatfish. Octo- 

 pus dofleini were the most impor- 

 tant invertebrate found in the diet 

 of sleeper sharks, representing 5% 

 of the total stomach contents 

 weight and 73% of the frequency of 

 occurrence. The estimated wet 

 weight o^ Octopus dofleini (based on 

 beak measurements) ranged from 

 5.65 kg to 29.07 kg (mean=18.51 kg; 

 SD=6.58 kg). The PULWL mea- 

 surements ranged from 23.3 mm to 

 36.5 mm (mean=31.78 mm; SD= 

 3.64 mm). Less important inverte- 

 brate prey included squids, snails 

 (Fusitriton sp.), hermit crabs, and 

 gammarid amphipods. Fish offal 

 (five arrowtooth flounder heads) 

 was found in one sleeper shark 

 stomach. It represented 12% of the 

 total stomach contents weight and 

 had a frequency of occurrence of 

 9% . No Steller sea lion parts were 

 found in the 13 sleeper shark stom- 

 achs examined. 



In our study, three specimens 

 were collected from bottom trawls, 

 ten from longline surveys. The 

 weight of stomach contents of the 

 three specimens collected from bot- 

 tom trawls (sharks no. 4, 12, and 

 13) were more than 2000 g (4506 g; 

 2321 g; and 11,782 g, respectively), 

 whereas weight of stomach con- 

 tents of the specimens collected 

 from long lines were much lower 

 than those collected from the bot- 

 tom trawls (only three weighed 

 more than 500 g, one weighed more 

 than 3000 g, and the rest weighed 

 less than 50 g). Less food in the 

 stomachs of the sleeper sharks col- 



Manuscript accepted 13 May 1998. 

 Fi.sh. Bull. 97:406-409 (1999). 



