- Understanding the movement behavior and foraging strategies of individuals across multiple spatial and temporal scales is essential not only for understanding the biological requirements of individuals but also for linking individual strategies to population level effects. Glacial fjords scattered throughout south-central and southeastern Alaska host some of the largest seasonal aggregations of harbor seals (Phoca vitulina richardii) in the world, and an estimated 15% of the harbor seal population in Alaska is found seasonally at these glacial ice sites. Over the last two decades, the number of harbor seals has declined at two of the primary glacial fjords, in Aialik Bay in south-central Alaska and in Glacier Bay in southeastern Alaska, thus raising concerns regarding the viability of seal populations in glacial fjord environments. From 2004-2009, the foraging ecology, diving behavior, and migration
patterns of harbor seals from Glacier Bay National Park, Alaska were examined in relation to prey availability and oceanographic features in Glacier Bay and the surrounding regions of southeastern Alaska. Time-depth recorders, very high frequency transmitters, and satellite-linked transmitters were used to quantify the vertical and horizontal movement patterns of harbor seals in the marine environment. Specifically, (1) I characterized the diving behavior, foraging areas, and foraging strategies of female harbor seals from terrestrial and glacial ice sites relative to prey availability during the breeding season (May-June) in Glacier Bay, (2) I quantified the intra-population variation in at-sea post-breeding season (September-April) distribution and movement patterns of female harbor seals in relation to oceanographic features, (3) I quantified the post-breeding season migration patterns of female harbor seals relative to the boundaries of the marine protected area of Glacier Bay National Park, and (4) I characterized the use of the continental shelf region of the eastern Gulf of Alaska by female harbor seals from Glacier Bay, both as a foraging area and as a migratory corridor in relation to oceanographic features.
During the breeding season, there was a substantial degree of intra-population variation in the diving behavior and foraging areas of juvenile and adult female seals from glacial ice and terrestrial sites in Glacier Bay. The presence of multiple diving strategies suggests that differences in the relative density and depth of prey fields in glacial ice and terrestrial habitats in addition to seal age and reproductive status may influence diving and foraging behavior of harbor seals.
During the post-breeding season, juvenile and adult female harbor seals ranged extensively beyond the boundaries of the marine protected area of Glacier Bay National Park, throughout the northern inshore waters of southeastern Alaska and the continental shelf region of the eastern Gulf of Alaska between Cross Sound and Prince William Sound, Alaska (up to 900 kilometers away). Seals exhibited a relatively high degree of intra-population variation in their at-sea post-breeding season distribution patterns that may be a function of extrinsic factors such as oceanographic characteristics, which can influence prey availability as well as intrinsic factors including previous experience with foraging areas and seal condition and age. Use of the continental shelf region of the eastern Gulf of Alaska by harbor seals as a foraging area may be due to enhanced biological productivity which may be associated with ephemeral hydrographic and/or static bathymetric features. Despite extensive migrations of seals from Glacier Bay during the post-breeding season, there was a high degree of inter-annual site fidelity of seals to Glacier Bay the following breeding season after seals were captured.