Site fidelity and dispersal patterns of domestic triploid steelhead trout (Oncorhynchus mykiss Walbaum) released to the wild

A combined acoustic and radio telemetry system was deployed within Bay d'Espoir. Newfoundland. to determine whether cultured steelhead trout (Oncorhynchus mykiss) released in the vicinity of a commercial aquaculture site remain at the site (site fidelity) or disperse from it. Two sets of fish releases (summer and winter 1998) were performed to determine seasonal effects on movements in the wild. Simulated escapes in summer involved 68 fish released from the cage system and 66 fish released from a cage towed approximately 1 km away from the grow-out site. The winter releases involved three batches of 30 fish each one from the cage system and two off-site over the side of a boat (at 200 and 1000 m distance) after transport on board with no cage towing involved. The results suggest site fidelity among steelhead released during the growing season. Fidelity was only slightly larger for on-sits releases than off-site releases. Off-site released steelhead make a rapid return to their rearing sites, suggesting homing behaviour. During thr winter. the movement to the overwintering release site was less directed with a higher degree of dispersal. Released steelhead eventually dispersed from the release site. and in both seasons displayed a directed movement to the hydroelectric spillway, which is also the location of the local salmonid hatchery. Implications of the results are discussed in light of the development of recapture methodologies for aquaculture salmonids. (C) 2001 International Council for the Exploration of the Sea.