A multi-scale analysis of habitat use by gray whales ( Eschrichtius robustus) in Clayoquot Sound, British Columbia, 1997--1999

Clayoquot Sound, an area on the west coast of Vancouver Island, British Columbia, Canada is a tertiary feeding area used by eastern gray whales ( Eschrichtius robustus). The objective of this study was to determine the role of depth and seafloor relief in whale feeding habitat selection. Results indicate that gray whale use of foraging habitat significantly varied spatially, between feeding sites, and temporally, within and between seasons. Most likely, prey type and biomass are more influential on whale distributions than water depth or seafloor slope. Used and unused water depth and seafloor slope categories by whales reflected within season and between season variability in the distribution and abundance of whale prey in the study area. Movement of whales from shallow to deep water in the study area as the season progressed was an artefact of the whales switching to planktonic and benthic prey from epibenthic prey. Because gray whales utilize different foraging areas in space and time in Clayoquot Sound, long-term management plans could predict and identify potential feeding areas along the entire coast of Vancouver Island and incorporate a sophisticated understanding of within season and between season prey and foraging site switching.