Hastings and Sydeman Population status of Eumetopim juhahis at tlie South Faiallon Islands, California 



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Figure 3 



Annual trends in counts of Steller sea lions at the South Farallon Islands from 1974 or 1977 to 1996 for (A) both sexes and all 

 age classes; (B) adult females; (C) subadult males; and (D) immature individuals and yearlings. Significant trends in counts, 

 after accounting for survey date ( residual centered about the mean count from Figure 2. square-root transformed ). are shown 

 for; all months (light dashed line); only counts during the breeding season (May - July; solid black line); and only counts from 

 late fall through early winter (September-December; solid light black line). Results of significance tests using square-root 

 and log-transformed counts were identical; Linear rates of change from log.-transformed counts are shown in Table 1. 



mals at the Farallon Islands are currently lower (0.06 

 of the 1989 statewide count, 0.09 of the count from four 

 major sites) than at the other three major California sites 

 (Alio Nuevo Island, St. George Reef and Sugarloaf Island) 

 which ranged from 0.16 to 0.18 of the 1989 statewide 

 count, and from 0.26 to 0.37 of the count from four major 

 sites (Loughlin et al., 1992). A smaller proportion of the 

 statewide Steller sea lion population has used the Farallon 

 Islands in recent years, compared with population counts 

 in the 1927-30 data, when Farallon animals accounted for 

 0.11 to 0.14 of the statewide count (Bonnet and Ripley, 

 1948). Historical pup production at the Farallon Islands is 

 unknown, but both the Farallon Islands and Ano Nuevo 

 Island were identified as the two largest and most impor- 

 tant Steller sea lion rookeries in the state in the early 

 1920s (Rowley, 1929). Pup production at the South Faral- 

 lon Islands over the past two decades has been very low 

 at <30 pups per year and in the last 10 years, at <10 



pups per year. Pup production since the mid-1980s, how- 

 ever, may be underestimated owing to the reduced prob- 

 ability of sighting pups since 1984 when pupping areas 

 shifted to West End Island, which is farther away from the 

 survey vantage points. Pup production at other major sites 

 in California included 117-137 pups at Sugarloaf Island 

 and Cape Mendocino in the early 1980s, 115 pups at St. 

 George Reef in 1994, and 230-243 pups at Ano Nuevo in 

 1993-94 (Westlake et al., 1997; NMML'). 



Reproductive rates of Steller sea lions at the South Far- 

 allon Islands were also low; an average of only 0.11 of fe- 

 males present during the breeding season produced pups. 

 This number may be biased low because some immature 

 males may have been included in the adult female count. 

 This ratio is much lower than that for rookeries in Brit- 

 ish Columbia (>0.70, Pike and Maxwell, 1958), Afio Nue- 

 vo, California (average of 0.40 to 0.50 from 1962-1990; Le 

 Boeuf et al.-') and Ugamak Island, Alaska, where ratio of 



