Hastings and Sydeman Population status of Eumetopias jubatus at the South Farallon Islands, California 



59 



2()()() -1 



1 750 



c 



3 1500 



•r. 



= I2?0 



i 1000 

 i 750 

 I 500 - 



o 



250 







• Siellcis - hiskinca! icnint-. 



O Slcllcrs iiiui Cajitoinuins ciinilimcJ - hislonciil coiinls 



 Slcllciv I'RBOcounls 



D Slclk-rs Miul C.ililomums coinhincd I'RHC.) cmmls 



- LiniitcJ lumrsr 1 



1920 1930 1940 1950 19(i0 1970 19X0 1990 2000 



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Figure 5 



Counts of sea lions at the Farallon Islands during the breeding seasons, from 

 1927 to 1997. Historical counts, 1927-.38: total count from single census per year 

 conducted by boat; includes North and South Farallones and adults and sub- 

 adults only (Bonnet et al., 1938). Historical counts, 1946-70: total count from a 

 single census conducted each year by airplane. Wimp, or boat; includes North 

 and South Farallon Islands and may include pups, subadults and adults. Steller 

 and California sea lions were not distinguished during these surveys. Instead 

 all sea lions north of Point Conception were considered Steller sea lions and 

 those south of Point Conception were considered California .sea lions (Bonnot 

 and Ripley. 1948; Ripley et al., 1962; Carlisle and Aplin, 1971 ). Point Reyes Bird 

 Obsei-vatory counts, 1974-97: maximum total counts during June and July from 

 weekly censuses at South Farallon Islands only (North Farallones excluded); 

 includes pups, immature individuals, subadults, and adults. Means or trends 

 over years are shown for Steller counts only (solid black lines) and for counts of 

 Steller and California sea lions combined (dashed linesA 



age classes after the breeding season may be a recent phe- 

 nomenon. Similarly. Steller sea lions of various sexes and 

 age classes were present off Humboldt County, California, 

 only from mid-April to September (Sullivan, 1980). 



Diverse seasonal patterns among sites were also evi- 

 dent in Canada and Alaska. In Canada, animals were 

 usually present year-round on rookeries and numbers 

 peaked during July, whereas year-round haulouts showed 

 no marked seasonal variation and a variety of sexes and 

 age classes were present in winter (Bigg. 1988). Winter 

 haulouts were occupied only in the winter and consisted 

 of either only males or a variety of sexes and age classes 

 (Bigg, 1988). In Alaska, many rookeries were abandoned 

 and some haulouts were occupied only in winter; other 

 haulouts and rookeries were occupied year-round (Ken- 

 yon and Rice, 1961; NMMLM. Major seasonal shifts in 

 distribution were not evident in Alaska, although winter 

 counts were substantially lower than summer counts and 

 there was a greater proportion of animals at haulouts 

 than at rookeries in winter ( NMML' ). The diversity in sea- 

 sonal patterns observed among sites (including rookeries 

 and haulouts) in California and elsewhere has confounded 

 generalizations concerning seasonal haulout patterns, al- 

 though a general shift from rookeries to haulouts in win- 

 ter seems to occur throughout most of the species range. 



Population status of Steller sea lions in southern and 

 central California 



Decline from historical numbers Substantial declines in 

 Steller sea lions at the Farallon Islands have been evident 

 since the 19'20s and in recent decades. Numbers declined 

 approximately 75-809( from an average of 600-790 ani- 

 mals from 1927 to 1947 to an average of 150 animals 

 (maximum count) from 1974 to 1997 (Fig. 5). This decline 

 may be overestimated because animals on the North Far- 

 allon Islands have not been included in sui-veys since 1970 

 and because more animals are likely visible by boat or air 

 than from island-based vantage points (Westlake et al., 

 1997). However, 85% to 90% of the island is visible from 

 vantage points and therefore effects of incomplete cover- 

 age should be small. Although the decline in numbers was 

 severe between 1938 and 1974, the rate of decline cannot 

 be determined for this period because surveys from this 

 period did not distinguish Steller from California sea lions 

 (Fig. 5). These surveys assumed that all sea lions north of 

 Point Conception were Steller sea lions and that all sea 

 lions south of Point Conception were California sea lions 

 (Carlisle and Aplin, 1971). Assessing the status of Steller 

 sea lions from the 1946-70 CDFG counts has been con- 

 founded by growth in the California sea lion population 



