Site fidelity of escaped rainbow trout to an experimental freshwater aquaculture facility and habitat overlap with native fish fauna

Abstract

The distribution and habitat use of escaped farmed fish is often difficult to assess after their dispersal from commercial open-pen aquaculture facilities. We examined site fidelity of rainbow trout Oncorhynchus mykiss after release from an experimental farm (escaped fish) in a small lake, as well as habitat overlap (3D kernel utilization distributions) with a native salmonid, lake trout Salvelinus namaycush. Fish were implanted with telemetry transmitters, and their movements were monitored by acoustic arrays during (2006-2007) and after (2008-2009) production of an experimental aquaculture facility in a small lake. This latter period allowed for assessment of habitat use by escapees in the absence of any influence of cage production, simulating conditions similar to fallowing or long-distance dispersal. Escaped rainbow trout were regularly present at the cage site (23% of total positions) during production, typically at times of the day which coincided with feeding, but were rarely near the cage site (2% of total positions) during the post-production period, and instead greatly increased their occupancy of the near-shore region. Lake trout did not display an affinity to the cage site in either the production or post-production periods (~1% of total positions), and volumetric overlap with rainbow trout was relatively low throughout the entire study. Our results indicate that in the absence of ongoing production at commercial aquaculture operations, rainbow trout escapees can readily switch to foraging on native fauna in the near-shore regions of the lake and did not directly compete with native lake trout.