570 



Fishery Bulletin 101(3) 



 Alaska YOY(n= 13) 



D Alaska yearlings (n=5) 



 Washington yearlings (n=7) 



^ 



£ 



ji 



n 



4-10 10-20 20-50 50-100 100-150 >150 



Depth bins in meters 



Figure 2 



Percentage of dives occurring in each dive-depth bin for Alaska young- 

 of-the-year (YOY), Alaska yearling, and Washington yearling Steller sea 

 lions. Twenty-five animals are represented from 1994 to 2000 and a total 

 of 222,073 dives. 



Results 



We report on SDR data obtained from 25 (13 male, 12 

 female) young-of-the-year and juvenile (estimated ages 

 of <2 yr) Steller sea lions from Washington state. Gulf of 

 Alaska, and Aleutian Islands, Alaska (Table 1). Most (22 

 of 25) were caught during October-March 1995-2000 and 

 the remainder during May-July (Table 1). Mean number 

 of days of transmission received from the SDRs was 56.8 d 

 (range 14.5-104.1 d). 



Dive characteristics 



We recorded over 222,073 dives for young-of-the-year and 

 juvenile Steller sea lions which had a mean dive depth of 

 18.4 m (range of means: 6.1-67.0 m; SD=16.23). Alaska 

 young-of-the-year dived to shallower depths and for shorter 

 periods (mean depth=7.7 m, SD=1.7; mean duration=0.8 

 min, SD=0.1; mean maximum depth=25.7 m, SD=16.9; 

 and maximum depth=252 m) than did Alaska yearlings 

 (mean depth=16.6 m, SD=10.9; mean duration=l.l min, 

 SD=0.4; mean maximum depth=63.4 m, SD=37.7; and 

 maximum dcpth=288 m), whereas Washington yearlings 

 dived the deepest and the longest (mean depth=39.4 m, 

 SD=14.9; mean duration=1.8 min, SD=0.6; mean maxi- 

 mum depth=144.5 m, SD=32.6; and maximum depth=328 

 m ). Alaska animals dived to much shallower depths ( mean 

 depth= 10.3 ml than animals from Shilshole,WA. There was 

 no significant difference in the mean dive depths among 

 locations in Alaska (P=0.8). Alaska animals, in compari- 

 son to the Washington animals, had a significantly greater 

 proportion of dives in the 4-10 m depth bin ( 707f , P<0.001) 

 than in the deeper depth bins. 



We compared the proportion of dives in the shallowest 

 bin (depth bin 4— 10 m ) for animals captured in Washington 

 state versus Alaska using a generalized linear model with 

 a binomial link function (McCuUagh and Nelder, 1989). 

 The proportion of shallow dives was significantly greater 

 (P<0.00 1 ) among the Alaskan animals ( 8 1 .47f ) than among 

 the Washington state animals (43.8%). Among the Wash- 

 ington state animals, the proportions of dives in the 1020 

 m depth bin (20.4%) and the 20-50 m depth bin (19.4%) 

 were similar; proportions of dives in the deeper depth bins 

 were progressively fewer (Fig. 2). Maximum and mean- 

 maximum dive depth were also greater for young sea lions 

 from Washington that dived to 141.5 m (SE=11.4) mean- 

 maximum depth versus 33.8 m (SE=7.2) for Alaska sea 

 lions (F=63.4, 23 and 24 df; P<0.001) (Table 2). We plotted 

 the maximum depth for each 24-h period by the number of 

 days in which the Argos satellite received a status message 

 (which contains maximum depth for 24 hours) and found 

 that with one exception ( PTT 14078 ), Washington yearlings 

 consistently dived deeper than their Alaska counterparts 

 (Fig. 3, A and B). Two of three Alaska young-of-the-year 

 were shallow divers and the third dived to 250 m once and 

 beyond 100 m on numerous occasions late in the track- 

 ing period (Fig. 3C). The maximum depth for all sea lions 

 that we studied was 328 m for a juvenile sea lion that was 

 equipped with a SDR at Shilshole, WA (PTT 21106); the 

 deepest dive for a yearling Alaska sea lion was 288 m (PTT 

 14078) (Fig. 3). 



Mean dive duration was 1.1 min for all young sea lions 

 (n =226,497 dives). Dive duration was significantly longer 

 for Shilshole sea lions (x=1.75 min; range: 0.95-3.10) com- 

 pared to Alaska sea lions (v=0.85 min; range: 0.61-1.86; 

 F=24.5, 23 and 24 df; P<0.001). Few dives were greater 



