Summer-time use of west coast U. S. National Marine Sanctuaries by migrating sooty shearwaters (Puffinus griseus)

Non-breeding sooty shearwaters are the most abundant seabird in the California Current Large Marine
Ecosystem (CCLME) during boreal spring and summer months. This, combined with relatively great
energy demands, reliance on patchy, shoaling prey (krill, squid, and forage fishes), and unconstrained
mobility free from central-place-foraging demands—make shearwaters useful indicators of ecosystem
variability. During 2008 and 2009, we used satellite telemetry to evaluate shearwater ranging patterns
throughout the CCLME and specifically within the US Exclusive Economic Zone (EEZ) among birds captured
at three locations: Columbia River Plume, WA; Monterey Bay, CA; and Santa Barbara Channel,
CA. Shearwaters ranged throughout the entire CCLME from southeast Alaska to southern Baja California,
Mexico. Within the EEZ during 2008 and 2009, shearwaters spent 68% and 46% of time over the shelf
(<200 m), 27% and 43% of time over the slope (200–1000 m), and 5% and 11% of time over the continental
rise and abyssal regions (>1000 m), respectively. In 2008 and 2009, shearwaters spent 22% and 25% of
their time in the EEZ within the five west coast National Marine Sanctuaries, respectively; high utilization
occurred in non-sanctuary waters of the EEZ. Shearwater utilization distribution (based on the Brownianbridge
movement model) among sanctuaries was disproportionate according to sanctuary availability
(based on area) within the EEZ. Shearwaters utilized the Monterey Bay sanctuary (2008, 2009) and the
Channel Islands sanctuary (2009) disproportionately more than other sanctuaries. Although all five sanctuaries
were used by shearwaters, waters outside sanctuary zones appeared significantly more important
and likely supported large aggregations of shearwaters. Utilization distributions among individual birds
from three discrete capture locations were variable and revealed greater similarity in space-use sharing
within capture-location groupings and during 2008 when shearwaters were more aggregated than in
2009. We identified several regional ‘‘habitat hotspot’’ areas, including the Columbia River Plume, Cape
Blanco, Monterey Bay, Estero/San Luis Obispo Bays, and the eastern Santa Barbara Channel through the
inner Southern California Bight.