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NOAA Technical Memorandum NMFS-AFSC-218

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Diving behaviors and movements of juvenile Steller sea lions (Eumetopias jubatus) captured in the central Aleutian Islands, April 2005


Population counts and pup production for Steller sea lions (Eumetopias jubatus) in the central Aleutian Islands (CAI) of the western distinct population segment (wDPS) continue to decline for unknown reasons. Due to paucity of telemetry data for this region, satellite-linked depth recorders were deployed on 16 juvenile Steller sea lions from 19 April to 2 May 2005 to gain a better understanding of their diving behaviors and habitat use. Overall, depths of dives (n = 89,993, = 11.8 m, SD = 12.6, med = 8.0, and range = 5.0 to 255.0), durations of dives (n = 155,620, = 0.8 min, SD = 0.6, med = 0.5, and range = 0.5 to > 13.0), trip durations (n = 553, = 14.0 hours, SD = 19.6, med = 10.7, and range = 0.3 to 280.0), and shore durations (n = 589, = 10.5 hours, SD = 7.1, med = 10.7, and range = 1.0 to 58.7) were similar to findings for Steller sea lions previously tagged in the CAI. Diel behaviors, ontogenetic trends, and movements displayed by juvenile Steller sea lions also were similar to past accounts. Relative to data reported for Steller sea lions from the eastern DPS, however, trip durations of sea lions reported herein were longer, whereas depths of dives were shallower and durations of dives were shorter.
A continuous-time correlated random walk model that was applied to the telemetry data was used to examine areas of predicted diving activity with respect to Steller sea lion designated critical habitat. Overall, the proportions of predicted locations associated with diving to > 4 m within zones of critical habitat appeared to reflect the proportions of Argos data well and results were similar to other reports. Additional models will be useful for examining sea lion movements and diving behaviors among regions and with respect to spatial management measures and environmental features.

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