MARINE SPACE USE BY MARBLED MURRELETS BRACHYRAMPHUS MARMORATUS AT A MAINLAND FJORD SYSTEM IN SOUTHEAST ALASKA

SUMMARY At-sea research on Marbled Murrelets Brachyramphus marmoratus has been dominated by observational surveys that provide little understanding of space use by individual birds. To quantify marine space use with spatially unbiased metrics, we used radio telemetry to record nest and at-sea locations of Marbled Murrelets during the 2007 and 2008 breeding seasons at Port Snettisham in southeast Alaska. We documented considerable inter-annual variation in marine space use, indicating that foraging conditions were more favorable for Marbled Murrelets in 2007 than in 2008. Fixed kernel density estimates (FKDE) of home range size (95% FKDE) were smaller on average in 2007 (98 ± 10 km 2 ) than in 2008 (158 ± 18 km 2 ), but did not differ by sex or breeding status. Individual core use areas (50% FKDE) were not randomly distributed in our study area, and locations of population-level foraging hotspots were identified. Two large foraging hotspots were located within Port Snettisham in 2007; hotspots were less concentrated and more numerous in 2008, including small hotspots near the mouth of Tracy Arm to the south. Mean (± standard error) daily marine commuting distance (over the ocean) between at-sea locations and nest sites was shorter in 2007 (12.0 ± 0.9 km) than in 2008 (20.0 ± 2.0 km). Our findings suggest variable but relatively good marine habitat for Marbled Murrelets at Port Snettisham and the Holkham Bay area to the south, where Tracy Arm and Endicott Arm converge. These marine areas should be prioritized for conservation of Marbled Murrelets during the breeding season.