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Fishery Bulletin 105(1) 



With the exception of the southernmost rookery at Ano 

 Nuevo Island and the (former) Farallon Islands rookery, 

 both greatly reduced from historical levels, pup produc- 

 tion has increased consistently throughout the range of 

 the eastern population over the past 25+ years. 



The total population-wide pup count in 2002 was 

 10,053 pups, of which 49% were found in southeastern 

 Alaska, 33% in British Columbia, 11% in Oregon, and 

 7% in California (Table 1). This represents minimum pup 

 production because some pups may have died and disap- 

 peared from rookeries prior to the survey, or were born 

 after the census. Following Trites and Larkin (1996), 

 we applied an arbitrary adjustment of 10%- to account 

 for pups that had been missed during our survey, giving 

 a pup production estimate of 11,060. Using life tables. 

 Calkins and Pitcher (1982) estimated the ratio of total 

 animals to pups in a stationary population would be 

 about 4.5:1. Our sensitivity analyses indicated that for a 

 population increasing at 3.1%, the ratio could be as low 

 as 4.2:1 if the growth were due to increased fecundity, 

 or as high as 5.2:1 if the growth was due to reduced 

 juvenile mortality (Table 2). The eastern population is 

 thus estimated to have numbered about 46,000-58,000 

 animals in 2002. During the 2002 survey, we actually 

 counted 45,378 animals (10,053 pups and 35,325 non- 

 pups) on rookeries and at haulouts. This count represents 

 an absolute minimum population size because not every 

 site was surveyed and some animals were absent from 

 rookeries and haulouts during the surveys and therefore 

 were not counted. 



The general sparseness and lack of standardization 

 of the pre-1970 counts prevents a rigorous comparison 

 of current and historical population levels; however 

 several clear patterns emerge (Appendix). In south- 

 eastern Alaska abundance was apparently quite low 

 during the first half of the 20"^ century, but numbers 

 have increased consistently since that time. We have 

 no explanation for the low numbers during the early 

 1900s because we are not aware of large-scale hunting 

 or predator control efforts. Numbers were high in Brit- 

 ish Columbia in the early 1900s but were then reduced 

 by about 70% by predator control and hunting. They 

 have since recovered to levels approximately two-thirds 

 of those of the early 1900s. Numbers on haulouts in 

 Washington State were severely reduced by bounty 

 hunting in the early to mid-1900s. Although there has 

 been substantial recovery, peak numbers still appear 

 to be only about half of levels of 1915. There are no 

 count data available for Oregon prior to 1968, but the 

 fact that about 4000 sea lions were killed for bounty 

 during 1925-29 would indicate a sizable population 

 at that time. There has been a substantial recovery 

 since the 1968 surveys. The California population was 

 apparently large during the early 1900s. Sites in south- 

 ern California began declining in the late 1930s and 

 that portion of the range was abandoned by the 1980s. 

 Numbers in central California remained high into the 

 1960s, then declined to low levels, and stabilized dur- 

 ing the 1990s. In northern California numbers were 

 likely reduced during the mid 1900s, but now appear 



to be approaching levels of the early 1900s. Overall, 

 the eastern population currently appears to be similar 

 in size to historical levels of the early 1900s; the large 

 population increase in southeastern Alaska balances out 

 the declines in the southern portion of the range. 



Although the number of rookeries used by the east- 

 ern Steller sea lion population has remained relatively 

 constant (range 10-13), their distribution has shifted 

 (Fig. 5). In the 2002 survey, the breeding population was 

 centered (the latitude of each rookery weighted by the 

 number of animals on it) at about 51.5°N (central British 

 Columbia coast). Just over half of the rookeries (7 of 13) 

 and births (57%) occurred north of that latitude, with the 

 northernmost rookery at 58.2°N. For the 2002 popula- 

 tion-wide survey, the pattern was similar for both pups 

 and total numbers (pups and nonpups), suggesting they 

 both provided an index of breeding distribution. In com- 

 parison, during the 1970s the breeding population was 

 centered at roughly 49.9°N (central Vancouver Island), 

 with the northernmost rookery at 54.8°N, representing 

 a northward shift of 0.5° of latitude or 65 km per decade. 

 In the 1920s, the breeding population was probably cen- 

 tered somewhere around 46.0°N (Washington-Oregon 

 border); only two small rookeries accounted for about 

 13% of total abundance situated north of 51.5°N (the 

 current center of pupping). At the southern end of their 

 range, the declines of Steller sea lions appear to have 

 begun in southern California (San Miguel) between the 

 late 1930s and 1950s, and were followed by declines in 

 central California between 1960 and 1990; however the 

 two northernmost sites in California exhibited relative 

 stability. Conversely, at the northern end of their range, 

 Steller sea lions probably began breeding in significant 

 numbers in southern southeastern Alaska (Forrester 

 Island) in the late 1940s or 1950s and extended their 

 breeding range to central southeastern Alaska (Hazy 

 Islands) in the early 1980s, and northern southeastern 

 Alaska (White Sisters) in the 1990s. Overall, the south- 

 ern end of the breeding range contracted by about 3° 

 latitude (330 km), and the northern limit was extended 

 by about 5° latitude (550 km). 



Discussion 



The population increases observed in recent years over 

 most of the range of eastern North Pacific Steller sea 

 lion population almost certainly represent recovery from 

 the impacts of prior predator-control programs, harvest- 

 ing, and indiscriminate killing that took place prior to 

 protection under the Canadian Fisheries Act of 1970 

 and implementation of the U.S. Marine Mammal Pro- 

 tection Act in 1972. The overall annual rate of increase 

 of 3.1% was widespread (from Oregon to southeastern 

 Alaska) and has been underway for at least 25 years, 

 and there is no evidence of it slowing with increasing 

 sea lion densities. The consistent, long-term observed 

 rate of increase of 3.1% throughout most of the range 

 of the eastern population is well below the theoreti- 

 cal maximum intrinsic rate of increase for pinnipeds 



