Summary: SIZE OF HARBOR SEAL FORAGING REGIONS RELATIVE TO HAUL-
OUT SITE, SEASON, AND HOME RANGE IN THE PACIFIC NW
K. Reuland1*, A. Thomas1, S. Peterson1, M. Lance2, S. Jeffries2, A. Acevedo-Gutiérrez1
1Dept. Biology, Western Washington University, 2Wildlife Science Program, Washington Dept. Fish & Wildlife
The designation of marine reserves in Washington State is expected to increase depressed fish stocks, with a concomitant response from predators. To predict the impact of predators on stock recovery one must understand their current foraging behavior. This
study aimed to characterize differences in foraging behavior for harbor seals in the Georgia Basin. We used satellite telemetry and time-depth recorders to identify core foraging locations and examine habitat use over time. Seals were tagged at two haul-out
sites: Padilla Bay Estuary (n = 12) and Bird Rocks (n = 12). Dive locations were estimated using an interpolated track derived from Argos satellite transmissions. Kernel density estimates were used to identify home ranges and core foraging areas. Foraging
locations were related to haul-out site: Padilla Bay seals typically foraged closer to or within the estuary, while Bird Rocks seals foraged in rocky reef areas. Although there were no significant differences when comparing breeding (July-October) and non breeding
(Nov-June) season home ranges between sites some trends were observed. Bird Rocks seals had smaller home ranges and foraging areas during the breeding season, while Padilla Bay seals had slightly larger home ranges, coupled with smaller foraging areas.
Results indicate that seals from Bird Rocks foraged near candidate reserve sites throughout the year while those from Padilla Bay did not. Understanding variations in foraging behavior between haul-out sites is important for understanding variation within the
entire population and also when considering the locations of marine reserves. The placement of a reserve in or near core foraging areas, where seals demonstrate continuous foraging pressure, may inhibit stock recovery and the realization of reserve goals.
Marine reserves aim to recover depleted fish stocks. In the Pacific NW the
potential establishment of marine reserves calls for examining harbor seal
foraging behavior to assess their potential impact on stock recovery.
Harbor seals in the Georgia Basin (Fig 1) haul-out in estuaries and on
rocky reef islands. Haul-out site type may influence habitat use and
foraging behavior, influencing predation pressure on prey associated with
different site types.