The Oceanic Habitats of Seabirds: Their Zonal Distribution Off Vancouver Island, British Columbia, Canada

Abstract

In the summer of 1986, seabirds were studied off southwestern Vancouver Island, British Columbia, to determine their oceanographic distribution. Birds were observed on monthly cruises aboard ships, with surveys often crossing the continental shelfbreak. The abundance of different seabird species varied seasonally, and was tied to physical ocean processes. In statistical analyses, significant differences were noted in species diversity among the following zones: nearshore; irregularities in the shelf; continental shelf; continental slope; continental rise; ocean basin. Average number of seabirds differed among the shelf and ocean basin zones. Adjacent zones were found to be similar most often in dendrogram analyses. The largest numbers of seabirds were found at the shelfbreak, where prey were concentrated, particularly above undersea canyons. At times large flocks were found inshore and around trawlers that were actively fishing. Concentrations peaked in September, due to the presence of both migrating seabirds and those leaving nearby nesting colonies. Sub-dividing the oceanic realm according to seabed topography is recommended in future seabird research to better utilize ship resources.