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Early ocean movements, residency, and survival of steelhead (Oncorhynchus mykiss) were examinedin Queen Charlotte Strait, a large (20 � 100 km 2 ) marine area separating Vancouver Islandfrom 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%) vacatedQueen Charlotte Strait within 1 week of release in freshwater. Relative marine survival of hatchery smolts surgically implanted1 month prior to release was id entical to that of wildsmolts implantedon the d ay 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 andwildsmolts may be fundamentally similar, but that the cumulative stress of transportation andsurgery may red uce post-surgery survival. Hatchery smolts movedat 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 (X55%), contradicting assumptions that the early marine phase is the critical periodfor d etermining salmon recruitment. r 2004 Elsevier Ltd. All rights reserved. |
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