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

Abstract

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 ~50%, with some fish recaptured up 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.

Native and exotic fishes in a Patagonian reservoir with rainbow trout cage culture: spatial and trophic resource use

“…the exotic rainbow trout (both farm escapees and wild) and the native P. trucha, the former dominating at shallow depths and the latter at greater depths. Escaped (ERT) and wild (WRT) rainbow trout each accounted for c. one third of the total littoral capture (<4 m), coinciding with other studies on depth distribution of farm escapees (Chittenden et al, 2011;Skilbrei, 2012;Patterson and Blanchfield, 2013). Diet differences between species were marked, paralleling the observed segregation by depth.…”

“…These cases highlight the importance of time since escape in the feeding behavior of ERT. In the Canadian lake Huron, normal growth of ERT recaptured next to and distant (500 m) from farms suggested consumption of wild food and/or farm pellets (Patterson and Blanchfield, 2013). In addition, stable isotope analysis showed that ERT captured in tributaries of this lake consumed wild prey, resembling WRT isotopic signals (Johnston and Wilson, 2014).…”

“…Farm escapees could affect wild fish behavior. Given that fish learn from the behavior and chemical cues of other fishes (Brown et al, 2003;Webster et al, 2008), the surface feeding and spatial use typical of rainbow trout farm escapees (Chittenden et al, 2011;Skilbrei, 2012;Patterson and Blanchfield, 2013) may influence the behavior of conspecifics, particularly those naïve fishes reaching the reservoir after birth in tributaries. In oligotrophic environments like those in Patagonia, where wild fish biomass is low (Quirós, 1990), the effect of the massive and sustained input of farm escapees on wild fish behavior is likely to be important, favoring a surface restricted distribution.…”

“…Ecological impacts include predation, competition and species replacement (Habit et al, 2010;Johnston and Wilson, 2014). A variable degree of escaped fish fidelity to farms has been reported, but dispersal does occur eventually, as does the major use of surface layers (Bridger et al, 2001;Skilbrei, 2010Skilbrei, , 2012Chittenden et al, 2011;Patterson and Blanchfield, 2013).…”

“…Salmonid escapees are expected to have long-term environmental effects on the receiving communities, given their high dispersion capacity and longevity, in addition to the high frequency and massive nature of escape events (Podemski and Blanchfield, 2006;Arismendi et al, 2009;Bourret et al, 2011;Patterson and Blanchfield, 2013). Ecological impacts include predation, competition and species replacement (Habit et al, 2010;Johnston and Wilson, 2014).…”