NOTE Lowry et al.: Seasonal and annual variability in the diet of Zalophus californianus 



333 



Table 2 



Prey found in scat samples (n ) and frequency of occurrence (expressed in %) for prey 

 found in 1085 California sea lion scats collected at San Nicolas Island, California, 

 1981-86. 



Prey 



Elasmobranchs 



Prionace glauca 



Cephalopods 



Loligo opalescens 



Octopus spp. 



Onychoteuthis borealijaponicus 



Abraliopsis spp. 



Gonatus spp. 



Gonatopsis borealis 



Chiroteuthis calyx 



Unid. Gonatidae 



Crustaceans 



Pleuroncodes planipes 



blue shark 



market squid 



octopus 



squid 



squid 



squid 



squid 



squid 



squid 



unid. cephalopod 



pelagic red crab 



unid. crustacean fragments 



0.1 



Algas 



Unid. Algae 



algae 



0.5 



Kenyon 1977, Bowlby 1981, Everitt 

 et al. 1981, Jones 1981, Bailey and 

 Ainley 1982, Antonelis et al. 1984, 

 Aurioles et al. 1984, Roffe and Mate 

 1984), but dietary diversity appears 

 to be rather low in each location 

 relative to the number of prey taxa 

 consumed rangewide. Our studies 

 of seasonal and annual variability in 

 diet of sea lions at San Nicolas Is- 

 land further support the classifica- 

 tion of California sea lions as plastic 

 specialists (Morse 1980). California 

 sea lions exploit a few resources at 

 a time, but prey composition of the 

 diet is temporally dynamic; they 

 capitalize on the more seasonally 

 abundant and accessible schooling 

 or aggregating prey. 



The dietary occurrence of the sea 

 lions' primary prey (northern an- 

 chovy, Pacific whiting, rockfish, 

 jack mackerel, and market squid) 

 appears to be related to the sea- 

 sonal and annual occurrence of 

 those prey species near San Nicolas 

 Island. Market squid were eaten 

 most often in autumn and winter in 

 most years corresponding with the 

 seasonal nearshore movements of 

 spawning squid in this area (Bed- 

 ford et al. 1983, Klingbeil 1986). 

 Market squid were not commonly 

 eaten by sea lions in 1983 and 1984, 

 a time when squid were uncommon 

 in the Southern California Bight (cf. 

 Bedford et al. 1983; Klingbeil 1984, 

 1985, 1986; Grant 1987). 



The presence of northern anchovy 

 in the diet of sea lions seems to be 

 related to the availability of anchovy 

 near San Nicolas Island. Northern 

 anchovy were uncommon near San 

 Nicolas Island from 1982 through 

 1984, but were quite abundant in 

 that area in 1985 and 1986 (Bind- 

 man 1986, Methot and Lo 1987). 

 Sea lions consumed northern an- 

 chovy frequently in all seasons in 

 1985 and 1986, but substantially 

 lower from 1981 through 1984, ex- 

 cept during winter when anchovy 

 were spawning and evidently nearer 

 to San Nicolas Island than in other 

 seasons. 



