Oncorhynchus mykiss escaped from commercial freshwater aquaculture pens in Lake Huron, Canada

The fate of farmed fish after escape from aquaculture operations, and their potential ecosystem impacts, remains a primary concern for the sustainable development of this industry. We simulated small- (< 50 fish) and large-scale (500 fish) escape events of rainbow trout Oncorhynchus mykiss from 2 commercial operations in the North Channel of Lake Huron, the site of greatest freshwater production in Canada. Individual fish were either implanted with telemetry transmitters (n = 120) or marked with external tags (n = 1000) to monitor their movements and estimate survival and growth upon recapture. Rainbow trout dispersed quickly from the farms, and overall showed variable levels of site fidelity (2 to 40% after 3 mo), with most fish returning to the farm sites on multiple occasions after departure. Released fish were often detected in near-shore areas or at neighbouring commercial operations, but escapees were capable of long distance movements (> 350 km), where they were located in rivers, open waters and in an adjacent Great Lake. Rainbow trout maintained high specific growth rates (average 0.33% d(-1)) in the wild, both at and away from the farms. Known survival of escaped fish after a 3 mo period following release was similar to 50%, with some fish recaptured up to similar to 2.5 yr after release. Angling and avian predation accounted for the majority of mortalities. The ability of farmed fish to survive, successfully forage near and far from aquaculture operations and their preponderance to occupy near-shore habitats provide a strong basis for understanding the potential risks that escaped fish may pose to the fish community of Lake Huron.