CA-01-09-001
Ecosystem experiment to assess environmental impacts of freshwater cage aquaculture

Cage-reared rainbow trout accounts for most of the freshwater aquaculture production in central Canada. Public concern over potential environmental effects is currently limiting the expansion of this industry. In particular, it is believed that organic wastes from cage farms may contribute to increased nutrient concentrations, increased algae growth, and reduced oxygen concentrations in fresh waters. 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. A small cage culture facility has been established in one lake at ELA. Rainbow trout fingerlings were stocked here, raised to market size, and harvested (10 tonnes of fish produced) during the 2003 open-water season using current culture practices. This will be repeated for at least one more year. Water quality, sediment quality, algae growth, 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. To date, we have not detected any substantial changes in environmental quality since fish culture began in the lake. Solid waste (manure and excess food) has 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. However, it is important to continue monitoring environmental quality to determine if significant effects arise over time with increased waste inputs. This research will provide a clearer assessment of the environmental effects of cage culture in fresh water.