Loughlin et al.: Diving behavior of immature Eumetopias lubatus 



579 



500'N 



54<'0'N 



74 O'W 



Figure 9 



The three types of movement exhibited by two immature Steller sea Hons 

 captured at Turf Point, Seguam Island, Alaska, in 2000. A long-range trip 

 (solid circles) >200 km is shown for PTT 14163 as it left and returned 

 to Turf Point. A transit trip (open triangles) for PTT 14111 is shown as 

 it left Turf Point and remained at the east end of Amlia Island where it 

 went on numerous short-range trips (shaded squares). 



occurs, the yearlings are forced to explore more areas to 

 acquire food for needed energy. Dives become deeper and 

 longer as these yearlings forage at different depths within 

 the water column. Just before their first birthday, many 

 of these young sea lions are capable of diving to the same 

 depths and for the same duration as those of many adults; 

 they also begin to forage at greater distances and for longer 

 periods. Juveniles that we studied had a mean dive depth 

 of 18.4 m and dive duration of 1.1 min compared to adult 

 females in Alaska that had a mean dive depth of 21 m and 

 dive duration of 1.4 min (Merrick and Loughlin, 1997). 

 Maximum depth in our study was 328 m for a Washington 

 juvenile and 288 m for an Alaska juvenile. Maximum depth 

 information for adult females in Alaska was not provided by 

 the instruments used by Merrick and Loughlin ( 1997); their 

 maximum depths were characterized by bin data only. They 



showed that about 5% of dives by adult females in winter 

 were greater than 250 m. In another study, adult females 

 in Alaska were equipped with early-style SLTDRs that had 

 features that recorded time-depth information and these 

 SLTDRs showed that the females frequently dived to 200 m 

 or more (Merrick et al., 1994). 



Schreer and Kovacs (1997) summarized maximum dive 

 depth and dive duration for air-breathing vertebrates and 

 developed predictive allometric equations for both param- 

 eters based on body mass. We fitted our Steller sea lion 

 body mass data to these equations to estimate maximum 

 dive depth (27.33M^'''*^), where Afj represents body mass 

 in kilograms, and maximum dive duration (6.22^/^"'"). We 

 found that the maximum dive depth equation provided rea- 

 sonably close estimates but that dive durations were typi- 

 cally overestimated (Table 3). In some cases measured and 



