Distribution and survival of farmed rainbow trout escaped from aquaculture operations in Lake Huron

Description

Farmed fish escape from freshwater net pens in small numbers due to losses associated with handling, or, infrequently, in large numbers due to storm damage. It is currently estimated that losses of farmed fish into Lake Huron represent ~1-5% of total cage production[2]. Escaped fish from aquaculture facilities can negatively impact native or naturalized fish populations through competition, predation and interbreeding[3-4], which has been expressed to be of concern for the Lake Huron area.

The fate of farmed fish after escape is poorly understood[5]. Yet, the extent to which escaped farmed fish might impact freshwater aquatic ecosystems or interact with native fish will be contingent upon their survival and distribution in the wild. There is strong evidence that domestic rainbow trout have greater growth, but much reduced survival compared to their wild counterparts[6]. Recent telemetry studies show farmed fish released from cage sites can disperse widely, have varying attraction to the cage site, and have low overall survival[7-9]. What proportion of escaped farmed fish survive and for how long, as well as their habitat use, are questions that need to be addressed for the Lake Huron area to understand the potential for interactions with native fish species.

Project objectives:

The research outlined in this proposal will focus on questions of distribution and survival of farmed rainbow trout that have escaped from commercial aquaculture operations in the Lake Huron area. Our general approach will be to mark and release farmed fish from open-pen cage sites to emulate both small- and large-scale ‘escape events'. The main objective of this study is to measure the dispersal, spatial distribution and habitat use of escaped rainbow trout. Through the release of small numbers of farmed rainbow trout outfitted with telemetry transmitters, we will determine the spatial extent of escapee movements and their potential for interaction with native fish species based on habitat selection. A focus of this research will be to quantify the extent to which escaped fish remain at the cage site after release. This information will be useful in determining whether escaped fish use the cage as a food source, and whether recapture efforts at the cage is a viable option. Another important component of this first objective is to determine the potential habitat overlap between escaped trout and lake trout (Salvelinus namaycush), as well as other fish species.

A second objective of this research is to assess the survival and growth of escaped fish. We will conduct large-scale releases of farmed fish (1,000) and incorporate survival models to accurately assess lifespan. Recapture data will provide growth rates for escaped fish, which are critical to understanding the potential impacts on native fisheries and food webs.

Program Name

Aquaculture Collaborative Research and Development Program (ACRDP)

Year(s)

2008 - 2011

Ecoregion(s)

Central Canada: Great Lakes, St. Lawrence Freshwater Drainage Basin

Principal Investigator(s)

Paul Blanchfield
Email: Paul.Blanchfield@dfo-mpo.gc.ca