102 



Abstract — The eastern Stellar sea 

 lion {Eumetopias jubatus) population 

 comprises animals that breed along 

 the west coast of North America 

 between California and southeast- 

 ern Alaska. There are currently 13 

 major rookeries (>50 pups): five in 

 southeastern Alaska, three in British 

 Columbia, two in Oregon, and three 

 in California. Overall abundance has 

 increased at an average annual rate of 

 3.1% since the 1970s. These increases 

 can largely be attributed to popula- 

 tion recovery from predator-control 

 kills and commercial harvests, and 

 abundance is now probably as high as 

 it has been in the last century. The 

 number of rookeries has remained 

 fairly constant {n = ll to 13) over the 

 past 80 years, but there has been a 

 northward shift in distribution of both 

 rookeries and numbers of animals. 

 Based on the number of pups counted 

 in a population-wide survey in 2002, 

 total pup production was estimated 

 to be about 11,000 (82% in south- 

 eastern Alaska and British Colum- 

 bia), representing a total population 

 size as approximately 46,000-58,000 

 animals. 



Abundance and distribution of 



the eastern North Pacific Steller sea lion 



(Eutnetopias jubatus) population 



Kenneth W. Pitcher^ 

 Peter F. Olesiuk^ 

 Robin F. Brown^ 

 Mark S. Lowry^ 

 Steven J. Jeffries^ 

 John L. Sease^ 

 Wayne L. Perryman^ 

 Charles E. Stinchcomb^ 



Lloyd F. Lowry^ 



Email address for K. W, Pitcher: 

 ken_pitcher@fishgame.state.ak.us 



' Division ol Wildlife Conservation 

 Alaska Department of Fish and Game 

 525 West 67"^ Avenue 

 Anchorage, Alaska 99518 



2 Pacific Biological Station 



Department of Fisheries and Oceans Canada 

 Nanaimo, BC V9T 6N7, Canada 



3 Marine Mammals Research Program 

 Oregon Department of Fish and Wildlife 

 7118 NE Vandenberg Avenue 

 Corvallis, Oregon 97330 



'' Southwest Fisheries Science Center 

 National Marine Fisheries Service, NOAA 

 8604 La Jolla Shores Drive 

 La Jolla, California 92037 



5 Marine Mammal Investigations 

 Washington Department of Fish and Wildlife 

 7801 Phillips Road SW 

 Lakewood, Washington 98498 



' National Marine Mammal Laboratory 

 National Marine Fisheries Service, NOAA 

 7600 Sand Point Way, NE 

 Seattle, Washington 98115 



^ 73-4388 Paiaha Street 

 Kailua-Kona, Hawaii 96740 



Manuscript submitted 28 March 2006 

 to the Scientific Editor. 



Manuscript approved for publication 

 21 June 2006 by the Scientific Editor. 



Fish. Bull. 107:102-115 (2007). 



The Steller sea lion [Eumetopias juba- 

 tus) rs the largest of the Otariidae 

 and inhabits the North Pacific Rim 

 from California to Japan. Individuals 

 breeding at rookeries^ located along 

 the west coast of North America from 

 California northward through south- 

 eastern Alaska (Fig. 1) to 144°W 

 longitude form a distinct population 

 segment, generally referred to as 

 the eastern population. Historically, 

 exchange of reproductive females with 

 the Steller sea lion population to the 

 north and west of 144°W longitude 

 has been extremely low as shown by 

 genetic studies (Bickham et al., 1996) 

 and resightings of marked animals 

 (Raum-Suryan et al., 2002). This indi- 

 cates that population changes have 

 been driven by birth and death rates 

 within each population because immi- 

 gration and emigration of breeding 

 females among populations were too 

 infrequent to affect population dynam- 

 ics. More recent genetic analyses have 

 confirmed the ancient divergence of 

 the eastern and western populations. 

 However, two new rookeries (White 

 Sisters and Graves Rocks, Fig. 1) at 



the northern end of the range of the 

 eastern population appear to have 

 been colonized by females from both 

 populations (O'Corry-Crowe et al., 

 2005). The number of western female 

 immigrants to the eastern population 

 has been small (in the 100s) to date, 

 has not had a major impact on the 

 growth dynamics of the overall east- 

 ern population and has been limited 

 to the extreme northern range of the 

 eastern population. However, the pres- 

 ence of breeding female immigrants 

 from the western population within 

 the range of the eastern population 

 indicates that our prior assumption 

 that population dynamics of the east- 

 ern population was completely driven 

 by internal rates of reproduction and 

 survival was incorrect for the past 

 several years. 



' For purposes of this paper, rookeries are 

 arbitrarily defined as traditional, ter- 

 restrial sites where >50 pups are born 

 annually. Other terrestrial sites used 

 by sea lions are referred to as haulouts. 

 Small numbers of pups are also born on 

 haulouts, but probably constitute <1% of 

 the total <100 in the eastern population. 



