452 



Fishery Bulletin 104(3) 



A St. George Island 



 St George Island scats 

 B St George Island spews 

 D Commercial trawl fishery 



L 



3 



Age class 



Figure 3 



Percent minimum number of individuals (MNI9r ) of walleye pollock iTheragra 

 chalcogramma) age classes recovered from northern fur seal (Callorhinus 

 ursinus) scats and spews containing measurable pollock otoliths collected 

 from rookeries on (A) St. George Island (1484 otoliths from 173 scat samples; 

 105 otoliths from 27 spew samples) and (B) St. Paul Island (17.827 otoliths 

 from 902 scat samples; 154 otoliths from 23 spew samples). Pribilof Islands. 

 Alaska, during the breeding season (late July-September). 1990-2000. Also 

 shown is the MNI'5 of walleye pollock age classes caught by the commercial 

 trawl fishery between August and September 1990-2000 in fishery manage- 

 ment areas surrounding the Pribilof Islands, Alaska. 



Island and St. Paul Island samples are likely related to 

 the availability of prey within reach of female fur seals, 

 which varies according to the physical and biological 

 environment surrounding each island (Sinclair et al.. 

 1994; Antonelis et al.. 1997; Robson et al., 2004). 



The occurrence of important prey species in scat sam- 

 ples was consistent with previous analyses of northern 

 fur seal scat and stomach samples. However, there were 

 considerable differences in prey occurrence between 

 spews samples and previous studies (Kajimura, 1984; 

 Sinclair et al., 1994, 1996; Antonelis et al., 1997). In 

 northern fur seal diet studies based on analysis of the 

 entire gastrointestinal tract adult females were found to 

 primarily consume juvenile walleye pollock and gonatid 



squid (Sinclair et al., 1994; 1996). Likewise, diet stud- 

 ies based on scat samples had the highest occurrences 

 of walleye pollock and gonatid squid (Antonelis et al., 

 1997). Although we observed a similar FO^ of walleye 

 pollock in our scat samples, the ¥0% of gonatid squid 

 and Pacific salmon were significantly higher among 

 spews compared to previous studies based on scat and 

 G.I. tract samples. Thus, it is likely that the importance 

 of some prey species, such as gonatid squids and Pacific 

 salmon, has been underestimated in previous diet stud- 

 ies (e.g., Antonelis et al., 1997). 



Significant differences in the size of Gb-Bm were 

 observed between scat and spew samples, demonstrat- 

 ing size-related digestive biases between sample types. 



