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'Es poir. Newfoundland. to determine whether cultured steelhead trout (Oncorhyn chus mykiss) released in the vicinity of a commercial aquaculture site rema in at the site (site fidelity) or disperse from it. Two sets of fish releas es (summer and winter 1998) were performed to determine seasonal effects on movements in the wild. Simulated escapes in summer involved 68 fish releas ed from the cage system and 66 fish released from a cage towed approximatel y 1 km away from the grow-out site. The winter releases involved three batc hes 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 ca ge towing involved. The results suggest site fidelity among steelhead relea sed during the growing season. Fidelity was only slightly larger for on-sit s releases than off-site releases. Off-site released steelhead make a rapid return to their rearing sites, suggesting homing behaviour. During thr win ter. 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 ha tchery. Implications of the results are discussed in light of the developme nt of recapture methodologies for aquaculture salmonids. (C) 2001 Internati onal Council for the Exploration of the Sea.