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Description:
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Recent studies indicate a 70 % decrease in the Alaskan Steller sea lion (SSL ) population
(ca . 5 % per year ) since the early 1980's . In accordance with a 1997 status classification of the
Western Steller sea lion (WSSL ) stock as endangered , the "critical habitat" for the species was to
be defined . This habitat has now been designated to include 10 -20 nautical mile buffer zones
around most rookeries and haulouts in the Gulf of Alaska (GOA ) and Aleutian Islands . However ,
these zones were based on limited , summer , foraging data .
The primary objective of this study was to characterize juvenile SSL diving behavior
and habitat use along the Kenai Peninsula and Prince William Sound (PWS ) from winter to
spring . Fifteen free ranging , subadult SSL of both sexes were captured and equipped with
satellite telemeters at five haulout sites in PWS and Resurrection Bay , Alaska . Telemeters
transmitted for an average of 122 days (range 38 -181 days ) . A total of 11 ,692 locations were
received and 217 ,419 dives recorded .
All sea lions exhibited localized movements parallel or close to shore (3 -15 km
offshore ) . Young of the year (YOY ) exhibited high site fidelity . Older juvenile sea lion lions
were less restricted in their movements and traveled greater distances (200 -400km ) visiting a
variety of islands , buoys , and other locations in PWS .
Most dives were short (mean duration = 1 .1 min ) and shallow (mean depth = 10 .8 m ) ,
with animals diving to an average maximum depth of 193 m . During winter (January and February ) , many dives ( >40 % ) occurred during the daytime (0900 -1500 LT ) . However , by April
and May this pattern shifted and the animals made most of their dives ( >40 % ) during the night
(2100 -0300 LT ) . This relationship was more pronounced for dives deeper than 20 m and
coincided with the seasonal increase in photoperiod .
Subadult SSL , especially YOY , remained within the 20 nautical mile coastal zone during
winter and spring . Shallow , nearshore waters provide important habitat during this critical
period of transition to nutritional independence . However , more conclusive data on SSL
foraging ecology is necessary to better understand locations and depths preferred by the species . |