Loughlin et al.: Diving behavior of immature Eumetopias lubatus 



571 



than 6 min (Fig. 4). There was a significant positive Un- 

 ear relationship between dive duration and dive depth 

 (r2=0.89, F=7.06, 1 and 23 df, P<0.001), and a significant 

 positive relationship between sea lion mass at the time of 

 capture and mean dive duration (r^=0.46, F=3.86, 1 and 

 20 df,P<0,001) but not girth (r2=0.10,F=1.62, land 14 df, 

 P=0.22). The relationship between dive duration and dive 

 depth for males was not different from that for females 

 (F=1.16, 2 and 21 df, P=0.33). The positive relationship 

 between dive duration and mass was likely driven by the 

 greater mass of the male sea lions because the relation- 

 ship was not statistically significant when the analysis was 

 restricted to females. 



Dive depth and duration showed an interesting ontoge- 

 netic trend. Alaska animals 7-10 months old typically had 

 a mean dive duration of <1 min and a mean dive depth of 

 about 10 m; by 11-12 months of age both increased, almost 

 doubling in most cases (Fig. 5). Although sample size was 

 small, this ontogeny of diving to deeper depths for longer 

 periods at about 11-12 months of age was evident in the 



percentage of time at depth (Fig. 6). There was a higher pro- 

 portion of time spent in the deeper depth bins during May 

 and June (at age 11 and 12 months, respectively) than when 

 younger, and the proportion of time hauled out was reduced 

 for the older animals. Interestingly, the decrease in dive 

 depth and dive duration for two Washington animals at 23 

 months of age (Fig. 5) corresponded with movement from 

 inside Puget Sound to deeper waters off the Washington 

 coast. 



The greatest proportion of all diving (37%) occurred dur- 

 ing 2100-0300 h; the least (about 16%) during 0900-1500 

 h (Fig. 7). There were no periods when young-of-the-year 

 or juvenile sea lions from any location did not dive. The fre- 

 quency distribution of dives was similar in all time periods 

 for all age groups from Alaska and Washington (Fig. 7). 



Distance and duration of trips at sea 



Mean distance of trips at sea for 564 measured trips of 

 the 25 study animals was 16.6 km (SD=44.9 km; range: 



