Loughlin et al.: Diving behavior of immature Eumetopias jubatus 



567 



behavior of a small sample of Steller sea lions in Alaska; 

 Loughlin et al. (19981 provided similar information for 

 Steller sea lions off the Kuril Islands, Russia. Merrick et 

 al. (1990) and Brandon (2000) presented information on 

 female pup-attendance behavior of sea lions with VHF 

 radio-transmitters off the Kuril Islands and Alaska, re- 

 spectively. These studies showed that during the breed- 

 ing season, adult female Steller sea lions generally spent 

 about half their time at sea on relatively brief (18-20 h) 

 foraging trips. Dives tended to be shallow (,v=21 m), brief 

 (.v=1.4 min), and frequent (about 13/h). Observations dur- 

 ing winter showed that females with suckling yearlings 

 (17-22 months of age) had feeding trips of about 2.3 days, 

 whereas those with young-of-the-year (5-10 months of age) 

 had trips lasting 0.9 of a day; time on shore for lactating 

 females of both groups averaged 14.2 hours (Porter, 1997). 

 Baba et al. (2000) were able to follow a yearling Steller sea 

 lion for 5 months using two location-only satellite trans- 

 mitters; one was attached to the top of the head and the 

 other on the back. This animal traveled from Hokkaido 

 to Sakhalin Island and throughout the southern Okhotsk 

 Sea. No dive data were obtained. 



Our objective is to present a description of the diving 

 behavior of juvenile Steller sea lions for the western stock 

 of Steller sea lions in Alaska and the eastern stock in Wash- 

 ington state. We deployed SDRs on juvenile Steller sea li- 

 ons over a broader geographical range in Alaska and over 

 a wider range of dates, providing a more comprehensive 

 picture of the diving behavior of young Steller sea lions. 

 Additionally, SDRs are now smaller and of higher quality, 

 so that more detailed information on diving behavior is 

 available. We then provide in the "Discussion" section a 

 comparison of the accounts in the present study to those 

 we published earlier on adult female diving behavior (e.g. 

 Merrick and Loughlin, 1997). 



Materials and methods 



We captured 25 free-ranging Steller sea lions of both sexes 

 from approximately 6-22 months of age at rookeries and 

 haul-out sites in the Aleutian Islands and Gulf of Alaska 

 (Table 1, Fig. 1 ) throughout the year from 1994 to 2000, and 

 during 1995-2000 at Shilshole Marina in Puget Sound, near 

 Seattle, Washington. Animal age was estimated by using 



