ANTONELIS ET AL.: SPRING AND SUMMER PREY OF CALIFORNIA SEA LIONS 



TABLE 1. — Percentage occurrence of all prey species identified from 

 195 California sea lion scats collected on San Miguel Island, Calif., 

 spring and summer, 1978-79. 



(35.99c) 2 , and northern anchovy (20.0%). All other 

 prey species occurred in <10.0% of the scats. 



Relative length and weight estimates of the four 

 major prey species and the information used to calcu- 

 late these estimates are shown in Figure 1 and Table 

 2, respectively. The length and weight information 

 for rockfish is from data reported by Philips (1964) 

 for one of the three species (5. paucispinis) repre- 

 sented in this study. 



Measurements of otoliths from Pacific whiting and 

 northern anchovy provided sufficient information to 

 compare changes in the size and age of each prey 

 group from 1978 to 1979. For Pacific whiting the 

 lengths of otoliths were significantly greater (W* = 



•'About 95Tc of the juvenile rockfish were yearlings and were in- 

 cluded in this three-species complex because their otoliths are too 

 similar to differentiate. 



5.82, P< 0.0001) in 1979 (x = 7.71 mm,n = 90) than 

 in 1978 (x = 6.71 mm, n = 132). From these otolith 

 measurements, we estimated the mean length of 

 Pacific whiting at 156 mm in 1978 and 176 mm in 

 1979. All of the Pacific whiting otoliths were obtained 

 from 1- and 2-yr-old fish. The occurrence of 1-yr-old 

 fish in the sea lion diet was estimated at 98.5% in 

 1978 and 70% in 1979. For northern anchovy, the 

 lengths of otoliths were significantly greater (W* = 

 4.36,P < 0.0001) in 1978 (j = 3.58 mm, n= 19) than 

 in 1979 (x = 3.01 mm, n = 75). For these otolith 

 measurements we estimated the mean length of 

 northern anchovy at 111 mm in 1978 and 92 mm in 

 1979. Although all age classes of northern anchovy 

 were recovered from the scats, there was a notable 

 change in the percent occurrence of yearling fish 

 from 1978 (42%) to 1979 (81%). 



The percentage of occurrence in the four major prey 

 species is shown for the spring and summer of 1978 

 and 1979 in Figure 2. From the three-way con- 

 tingency table analysis, it was determined that 

 Pacific whiting occurred significantly more frequent- 

 ly in 1978 than in 1979 (P < 0.01), and there was a 

 greater percentage of occurrence in spring than in 

 summer (P < 0.01). For rockfish, there was no signifi- 

 cant difference in occurrence between years; 

 however, there was a greater percentage of 

 occurrence in the summer than in spring (P < 0.01). 

 The percentage occurrence of northern anchovy was 

 not significantly different between season, but there 

 was a significantly greater occurrence in 1979 than 

 in 1978 (P < 0.01). The relative proportion of oc- 

 currence for the two seasons for each year was 

 significantly different (P < 0.01) for Pacific whiting, 

 rockfish, and northern anchovy. Tests of significance 

 could not be done for market squid because of the 

 strong three-way interaction between occurrence, 

 season, and year. It is apparent, however, that the 

 percent occurrence of market squid did increase 

 from spring to summer during both years of the study 

 (Fig. 2). 



Table 2.— Information used in estimating the length of the four major prey species identified from 

 the scats of California sea lions, on San Miguel Island, Calif., 1978-79. 



Prey species 



Regression 

 equation 



R 2 



Reference 



Market squid 



Y = 0.243 + 0.0481X 



60 0.974 upper hood dorsal mantle Kashiwada 



length (mm) length (mm) etal. 1979 



Pacific whiting Y = 26 2 + 19.38X 84 977 fork otolith This study 



length (mm) length (mm) 



Juvenile rockfish' (') 155 (') (') Phillips 



1964 



Northern anchovy Y = -8 4946 + 33 216X 677 0.774 standard otolith Spratt 



length (mm) length (mm) 1975 



'Length measurements are from yearling bocaccio. Sebastes paucispinis. 



69 



