Blue whale habitat and prey in the California Channel Islands

Whale Habitat and Prey Studies were conducted off southern California durin g August 1995 (WHAPS95) and July 1996 (WHAPS96) to (1) study the distributi on and activities of blue whales and other large whales, (2) survey the dis tribution of prey organisms (krill), and (3) measure physical and biologica l habitat variables that influence the distribution of whales and prey. A t otal of 1307 cetacean sightings included 460 blue whale, 78 fin whale and 1 01 humpback whale sightings. Most blue whales were found in cold, well-mixe d and productive water that had upwelled along the coast north of Point Con ception and then advected south. They were aggregated in this water near Sa n Miguel and Santa Rosa Islands, where they fed on dense, subsurface layers of euphausiids both on the shelf and extending off the shelf edge. Two spe cies of euphausiids were consumed by blue whales, Thysanoessa spinifera and Euphausia pacifica, with evidence of preference for the former, a larger a nd more coastal species. These krill patches on the Channel Island feeding grounds are a resource exploited during summer-fall by the world's largest stock of blue whales. (C) 1998 Elsevier Science Ltd. All rights reserved.