Changes in the Immature Growth Rates of a Native Salmonid in Response to an Experimental Caged Aquaculture Operation

Caged aquaculture is the primary form of freshwater fish aquaculture practiced in Canada and contributes millions of dollars to the economy each year. However, these operations have potential environmental impacts, and their effects on native fish remain poorly understood. Here we report changes in the immature growth rates of lake trout (Salvelinus namaycush) from a small lake at the IISD- Experimental Lakes Area in response to the introduction of a caged rainbow trout (Oncorhynchus mykiss) aquaculture operation. The introduction of the aquaculture operation resulted in major shifts in the forage base of the lake, including an increase in the abundance of minnows and a decrease in the abundance of Mysis diluviana, an important component of immature lake trout diets. We tested whether the decreased abundance of Mysis negatively affected the growth rates of immature lake trout. Changes in the growth rates of individual lake trout were assessed by back-calculating length-at-age data using archived ageing structures. Preliminary results show an increase in Fulton’s condition factor (K) for immature lake trout year classes during the operation. This study will provide insight into the sometimes complicated effects of caged aquaculture operations on native salmonids.