CA-05-01-003
Ecosystem experiment to assess environmental impacts and recovery from freshwater cage aquaculture

The purpose of this project is to identify and quantify the environmental effects of rainbow trout cage culture on a lake ecosystem. This research is being conducted at the Experimental Lakes Area (ELA) in northwestern Ontario. Rainbow trout fingerlings were stocked in one lake, raised to market size, and harvested (10 tonnes of fish produced) during the 2003, 2004, and 2005 open-water seasons (ice free) using current cage culture practices. Water quality, sediment quality, periphyton, plankton, and invertebrate communities are all being monitored in this lake and in a nearby reference lake in the year before, and during the operation of this fish culture facility. Through 2004, substantial changes in environmental quality were not detected. Solid waste (manure and excess food) settled in a very localized area immediately beneath the cage. Dissolved nutrient concentrations, dissolved oxygen levels and algae growth in the lake are similar to pre-farming conditions. The cage facility will be operated for one more growing season before removal in late fall, 2006. The monitoring program will continue through 2008 as the ecosystem ‘recovers' from the cage aquaculture perturbation. A subset of the monitoring program is also being conducted in the area of an existing cage facility in the North Channel of Lake Huron as a comparator to the experimental systems.

Native fish populations in the experimental lake and in nearby control lakes are being studied to determine the effects of the culture operation on their abundance, survival, growth, reproduction, and behaviour. Lake trout initially avoided the aquaculture pen after installation, but reverted to their original movement patterns later in the year. There were no apparent effects of the cage culture operation on other aspects of lake trout biology. In contrast, smaller-bodied forage fishes appeared to be attracted to the net cage. Native fish community responses to the cages will continue to be assessed through fall 2008.