Movement and mitigation of domestic triploid steelhead trout (Oncorhynchus mykiss) escaped from aquaculture grow-out cages

Bridger, Christopher J. (2002) Movement and mitigation of domestic triploid steelhead trout (Oncorhynchus mykiss) escaped from aquaculture grow-out cages. Masters thesis, Memorial University of Newfoundland.

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Abstract

Cultured fish may occur in the wild from intentional release for restocking and sea ranching purposes or aquaculture escapees from ocean grow-out facilities. Aquaculture facilities lose some individuals during the production cycle, especially when sea cages are used. In addition to economic loss incurred to the fish farmer from escapement, potential disease, ecological and genetic interactions between escapees and wild conspecifics are of concern. In this study I monitored escapee movement, by tracking transmitter-implanted domestic female triploid steelhead trout in the wild using sophisticated biotelemetry fixed data-logging and manual tracking techniques, in Bay d'Espoir, Newfoundland, Canada. Of the 68 triploid steelhead released on-site, in July 1998,51 (75%) remained within a 500 m radius of the summer grow-out site 32 days after release. Similar to on-site released triploid steelhead, 17 of 66 (26%) triploid steelhead released approximately 1000 m outside of the summer grow-out site returned to the site within 4 hours of release. Subsequent tracking found that an additional 26 triploid steelhead had returned to the summer grow-out two days after release, bringing the total number of off-site released triploid steelhead return to 65%. Triploid steelhead trout released during the winter displayed lower fidelity than those released in summer. -- Dispersing triploid steelhead during summer were detected in the vicinity of other salmonid aquaculture sites throughout the bay. Summer and winter released triploid steelhead both displayed a directed movement upstream towards the hydroelectric spillway - also the location of the local salmonid hatchery. Results suggest escaped triploid steelhead trout may survive in the wild - moving between summer grow-out sites and the hydroelectric spillway, while feeding on excess farm feed during the summer season. A biotelemetry methodology was developed, and also described herein, to monitor and optimize potential recapture traps for the salmonid aquaculture industry. Recapturing escapees aggregating near aquaculture sites may help mitigate negative implications through removal of escapees from the wild.

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