Sinclair et al.: Prey selection by Callorhinus ursmus 



45 



59° N 



• Seal samples (all years) 

 D Marinovich midwater trawls 

 A Diamond midwater trawls 



Middle Shelf Domain 



Figure 1 



The study area with midwater trawl locations and northern fur seal collection positions. All 

 midwater trawls were conducted in 1985. Seal numbers 1-17 were collected in 1981, 18-40 were 

 collected in 1982, and 41-83 were collected in 1985. 



1982; and from 6 to 16 August 1985. Collections 

 were made within 185 km of the Pribilof Islands 

 over the continental shelf, continental slope, and 

 oceanic domain of the eastern Bering Sea (Fig. 1). 

 Seals were shot from a small craft and returned 

 to the NOAA ship Miller Freeman (65-m stern 

 trawler) for examination within 1.5 hours of collec- 

 tion. The esophagus of each seal was checked for 

 food as an indication of regurgitation, and the gas- 

 trointestinal (GI) tract was removed and frozen. 

 Gastrointestinal tract contents were later thawed 

 and gently rinsed through a series of graded sieves 

 (0.71, 1.00 or 1.40, and 4.75 mm in 1981 and 1982; 

 0.50, 1.00, 1.40, and 4.75 mm in 1985). Fleshy re- 

 mains were preserved in 10% formalin. Fish otoliths 

 and bones were stored dry. Cephalopod rostra and 



statoliths were preserved in 70% isopropyl alcohol. 

 Prey identification was based on all remains, in- 

 cluding otoliths. Otoliths were not used for fish iden- 

 tification in earlier fur seal diet studies because 

 stomach samples were stored in formalin, which 

 dissolves otoliths. Techniques and references for the 

 identification of prey based on otoliths include Fitch 

 and Brownell (1968), Morrow (1979), Frost and 

 Lowry (1981), and otolith reference collections (see 

 Acknowledgments). References for cephalopod beak 

 and statolith identification include Clarke (1962), 

 Young (1972), Roper and Young (1975), Clarke 

 (1986), and beak and statolith reference collections 

 (see Acknowledgments). A tooth was collected from 

 each fur seal that was shot and ages were derived 

 from direct readings of canine tooth sections follow- 



