Early ocean survival and marine movements of hatchery and wild steelhead trout (Oncorhynchus mykiss) determined by an acoustic array: Queen Charlotte Strait, British Columbia

Early ocean movements, residency, and survival of steethead (Oncorhynchus mykiss) were examined in Queen Charlotte Strait, a large (20 x 100 km(2)) marine area separating Vancouver Island from the mainland. The results provide the first detailed data on the ocean biology of hatchery and wild steelhead smolts. Initial ocean movements were not strongly directed, with most smolts swimming in the range of 0.2-0.5 body length (BL)s(-1). The majority (78%) vacated Queen Charlotte Strait within 1 week of release in freshwater. Relative marine survival of hatchery smolts surgically implanted 1 month prior to release was identical to that of wild smolts implanted on the day of release; survival of hatchery smolts transported to the study site, implanted, and released all on the same day was significantly lower. The results suggest that the early marine survival of hatchery and wild smolts may be fundamentally similar, but that the cumulative stress of transportation and surgery may reduce post-surgery survival. Hatchery smolts, moved at higher average swimming speeds than wild smolts, but the difference was not statistically significant. Early marine survival within the study region appears to be relatively high (greater than or equal to 55 %), contradicting assumptions that the early marine phase is the critical period for determining salmon recruitment. (C) 2004 Elsevier Ltd. All rights reserved.