FISHERY BULLETIN: VOL. 82, NO. 1 



1979 



10 20 30 40 50 60 70 80 90 100 

 Percentage 



FIGURE 4.— Percentages of the total estimated weight for the four major prey species in spring and summer, 



1978-79. 



the type of large, dense schooling prey which are 

 commonly fed upon by many of the pinnipeds in the 

 coastal waters off California (Antonelis and Fiscus 

 1980). Furthermore, the variety of food items re- 

 ported in this and other studies (Jameson and Kenyon 

 1977; Morejohn et al. 1978; Bowlby 1981; Jones 

 1981; Ainley et al. 1982) indicates that California sea 

 lions are capable of foraging on a wide range of fish 

 and cephalopods. 



The range in the average length estimates of the 

 four major prey species (95-171 mm) does not exhibit 

 a great diversity in size, and may reflect a size pref- 

 erence for sea lions feeding in the waters near San 

 Miguel Island. Both Pacific whiting and rockfish 

 attain a much larger size as adults (Phillips 1964; 

 Dark 1974), while the length estimates of northern 

 anchovy and market squid are within the size range of 

 juveniles and adults (Fields 1965; Spratt 1975). 



As more information is obtained on the prey and the 

 foraging behavior of California sea lions, researchers 

 will attempt to evaluate the biomass of each prey 

 species consumed (Bailey and Ainley 1982). These 

 types of studies require information on the variations 

 in the diet of California sea lions throughout their 

 range. For this reason, we compare the estimated 

 length data of market squid and Pacific whiting from 

 this study with similar information reported in areas 

 north of Point Conception. The estimated lengths 

 were similar for market squid which were preyed 

 upon by California sea lions in Monterey Bay, Calif. 



(Morejohn et al. 1978) and in the waters near San 

 Miguel, with mean values of 130 mm (Morejohn et al. 

 1978, estimated from figure 27) and 127 mm, respect- 

 ively. California sea lions foraged on all age classes of 

 market squid in both areas. For Pacific whiting, 

 however, differences between the northern and 

 southern range of the California sea lion were 

 apparent, with estimated length averages ranging 

 from 250 to 360 mm at Southeast Farallon Island, 

 Calif. (Bailey and Ainley 1982) compared with an 

 average of 166 mm at San Miguel Island. Primarily 1- 

 and 2-yr-old fish were preyed upon near San Miguel, 

 while 2- and 3-yr-old fish were reported as prey at 

 Southeast Farallon. 



From these comparisons, we assume that squid of 

 all sizes and age classes will be preyed upon by 

 California sea lions, in both their breeding and non- 

 breeding ranges. For Pacific whiting, however, there 

 are apparent differences in the size and age classes 

 consumed by California sea lions in the two areas. 

 These differences could be related to three possible 

 factors: 1) There could be differential feeding 

 according to various age and/or sex classes of sea 

 lions which occur in the two areas. When present, 

 there are mostly subadult and adult males at 

 Southeast Farallon Island, and at San Miguel Island 

 there are comparatively fewer subadult and adult 

 males and many more females and juveniles of both 

 sexes (Peterson and Bartholomew 1967; Le Bouef 

 and Bonnell 1980; Ainley et al. 1982). 2) Differences 



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