FISHERY BULLETIN: VOL. 80, NO. 2 



Table 1.— Percent composition of California sea lion diet as determined by otoliths and beaks 

 regurgitated at haul out sites, Southeast Farallon Island, 1974-78. 



IOO 



z 

 cr 



o 



< 



< 

 I- 

 o 



o IOO" 



o 



o 



I967 69 71 



Figure 4.— The total catch of whiting in the Pacific coast fish- 

 ery and the proportion of that catch taken off California, 1967- 

 79. 



df = 10, P<0.01, Spearman rank correlation). 

 Considering the whole coast of California, trawl- 

 ers concentrated near the Farallones, at least 

 from 1974 to 1976, when fishery surveillance rec- 

 ords were available to us. If we assume that the 

 number of trawlers and the prevalence of whit- 

 ing in sea lion diets, in conjunction with sea lion 

 population size, reflect whiting availability, we 

 conclude that both sea lions and humans were 

 attracted to continental slope waters at the same 

 time in order to catch whiting. The only differ- 

 ence was that the sea lions departed at the peak of 



Table 2.— Number of stern trawlers fishing for Pacific whit- 

 ing over the California continental slope between lat. 39° and 

 37°N from January through December 1974-77; data summar- 

 ized from NMFS monthly surveillance reports. 



Year 



M 



M 



O N 



harvest in order to return to traditional breeding 

 sites. 



Associated with the unavailability of whiting, 

 both fishing activity and the preponderance of 

 whiting in the sea lion diet dropped off from Sep- 

 tember to March. During the winter months 

 adult whiting migrate off the continental shelf to 

 spawn in deeper waters of the continental slope 

 (Bailey 1980), and juveniles probably show the 

 same behavior. In addition, during the spawning 

 months they do not diurnally migrate but remain 

 deep (Nelson and Larkins 1970). They are thus 

 unavailable to both the fishery and the sea lions. 



We offer the following hypothesis to explain 

 the patterns observed in the sea lions' behavior. 

 First, they are attracted to continental slope 

 waters of central California by whiting which, 

 due to their own migrations, become available 

 there during spring and summer. The trawler 

 fishery, also attracted by greater fish availabil- 

 ity, was perhaps depleting whiting stocks sea- 

 sonally to such an extent during the early to mid- 

 1970's that by late summer when sea lions were 



256 



