lar and weekly during following years to Janu- 

 ary 1980. They were made year-round and oc- 

 curred after 1400 h when maximum numbers 

 of sea lions haul out at Southeast Farallon (Fig. 

 1; see also Mate 1975). In the following analyses 

 the 1971-73 censuses were combined (Fig. 2) to 

 correct for sporadic coverage. During censuses 

 in the last 9 mo of both 1975 and 1976, and in all 

 censuses since, animals were differentiated into 

 adults and subadults, virtually all of which were 

 males. Total count results are presented in 

 Huber et al. (footnote 4). 



Whiting otoliths and squid beaks were col- 

 lected at regular biweekly intervals from the 

 boat dock at North Landing, Southeast Farallon 

 Island. This is a favored haul out site for Califor- 

 nia sea lions but not for other pinnipeds. Whiting 

 otolith radii were measured and prey length was 

 determined from the relationship of fish length 

 to otolith radius. We assume that significant dis- 

 solution of otoliths did not occur as a result of 

 digestion. Prey totals were determined by divid- 

 ing otoliths by two and taking the higher number 

 of upper and lower squid beaks. 



Counts of trawlers fishing for whiting were 

 made by the Division of Enforcement and Sur- 

 veillance, National Marine Fisheries Service. 

 Catch statistics were made available by the 

 Northwest and Alaska Fisheries Center, NMFS. 



120 



to I i o 



z 



o 100 



~ 90 



80 



u ™\ 



CO 



60 

 <E 50' 



LU 



40 



CD 



30 

 20 



10 



o 



en 

 O 

 O 



o 

 ->l 



o 

 o 



o o 



CO CO 



ro uj 

 o o 

 o o 



en ai 

 o o 



CO CD 



o o 



10 



o 



TIME OF CENSUSES 



Figure 1.— The number of California sea lions hauled out 

 during hourly periods at Shubrick Point, Southeast Farallon 

 Island; the mean and ± standard deviation are shown based on 

 12 all-day watches during April and May 1974. 



FISHERY BULLETIN: VOL. 80, NO. 2 



RESULTS AND DISCUSSION 



California Sea Lion Biology 



Aside from the one pup born at Southeast 

 Farallon, every year since 1974 except 1978 (plus 

 its mother and at least one bull) (Pierotti et al. 

 1977; Huber et al. [footnote 4]; Point Reyes Bird 

 Observatory unpubl. data), the California sea 

 lion population was comprised of nonbreeding 

 males. Major breeding sites are located in the 

 southern California islands (Bartholomew 1967; 

 LeBoeuf and Bonnell 1980). From 1971 to 1976 a 

 large peak in numbers was reached each year at 

 the Farallones in late April or early May, when 

 animals migrating south toward southern breed- 

 ing sites hauled out for short periods (Fig. 2). A 

 majority of animals departed (temporarily?) 

 each evening to feed (Hobson 1966); about an 

 hour after dawn they began to return and by 

 early afternoon maximum numbers were hauled 

 out. Numbers present each day rapidly declined 

 in late May, and by late June only a few Zalophus 

 hauled out. Population size increased again in 

 late July, reached a peak in August or Septem- 

 ber that was much smaller than in spring, and 

 than declined to a level maintained through the 



<" 500- 



z 

 o 





1977-80 



EC 



LU 

 [TJ 



3 



Z 500- 



Figure 2.— The mean ( ± standard deviation) number of Cali- 

 fornia sea lions hauled out at Southeast Farallon Island each 

 month during two periods: 1971/73-76 and 1977-80; below each 

 curve are the number of censuses each month and above are the 

 proportion of adults present. 



254 



