Brandon et al.: Neonatal growth of Eumetopias /ubatus 



247 



~65°N 



- 60° 



-55° 



180° 

 1 



Bering Sea 



Sequam 



Island Yunaska 

 >j^ Kl, Hid 



■to.*.* 



\ 



^teutian Islands 



Chinkof Island 



Lowrie - 

 Island 



250 miles 



170° 



/ 



160° 



I 



150°W 

 I 



250 kilometers 

 1 



Figure 1 



Study sites for Steller sea lions iEumetopias jubatus) in Alaska. The Lowrie Island rookery in south- 

 east Alaska has a stable population but rookeries at Fish, Marmot and Chirikof Islands in the Gulf of 

 Alaska and Yunaska and Seguam Islands in the Aleutian Islands are areas where the population of 

 Steller sea lions has declined. 



lation decline (>80'7f) occurred in the western popula- 

 tion between the 1970s and the 1990s. In 1997, these 

 population changes led to the reclassification of the 

 western population from "threatened" to "endangered" 

 and a classification of the eastern population as "threat- 

 ened" under the Endangered Species Act (U.S. Federal 

 Register 62:24345-24355). 



One hypothesis for the decline in population of SSLs 

 is a decrease in food availability or quality in the Gulf 

 of Alaska and the Aleutian Islands (Pascual and Adki- 

 son, 1994; York, 1994; Calkins et al., 1999; NMFS 1 - 2 ). 

 If females are unsuccessful in obtaining sufficient food, 

 pups will develop more slowly or die because of a de- 

 crease in milk supply. To examine the potential effects 



NMFS (National Marine Fisheries Service). 1992. Re- 

 covery plan for the Steller sea lion tEumetopias jubatus), 

 92 p. Prepared by the Steller Sea Lion Recovery Team for 

 the National Marine Fisheries Service, Silver Spring, MD. 

 [Available from the National Marine Mammal Laboratory, 

 7600 Sandpoint Way. NE, Seattle, Washington 98115.) 

 ; NMFS (National Marine Fisheries Service). 1995. Sta- 

 tus review of the United States Steller sea lion (Eumeto- 

 pias jubatus) population. 61 p. Prepared by the National 

 Marine Mammal Laboratory, Alaska Fisheries Science 

 Center. [Available from the National Marine Mammal Labo- 

 ratory, 7600 Sandpoint Way, NE, Seattle, Washington 98115.] 



of food availability on pup development, we measured 

 growth rates of male and female pups from stable and 

 declining populations of SSL in Alaska from 1990 to 

 1997. Our null hypothesis was that there was no differ- 

 ence in pup growth rates among rookeries in southeast 

 Alaska, the Gulf of Alaska, and the Aleutian Islands. 

 The alternative hypothesis was that pups grew at a 

 faster rate in southeast Alaska, the area of stable popu- 

 lation. However, our results showed that pups grew 

 faster in the area of declining population during the 

 first six weeks after birth. In addition, females invested 

 more energy in male pups at all locations during gesta- 

 tion, but not during early lactation. 



Materials and methods 



Animals and study sites 



From 1990 to 1997, SSL pups were studied at loca- 

 tions in southeast Alaska, the Gulf of Alaska, and the 

 Aleutian Islands (Fig. 1 and Table 1). At Lowrie Island 

 <54°51'N, 133°32'W) in southeast Alaska, measure- 

 ments were made in 1993, 1994, and 1997. The rookery 

 at Lowrie Island is in the area of the stable population 

 (Calkins et al., 1999). In the Gulf of Alaska, measure- 



