Predicting the location of optimal habitat boundaries for lake trout (Salvelinus namaycush) in Canadian Shield lakes

The optimal habitat boundary for lake trout (Salvelinus namaycush Walbaum) has been defined as that portion of the lake having both more than 6 mg.L-1 oxygen and temperature less than 10 degreesC. Here we use an existing hypolimnetic oxygen model to define the lower boundary of the optimal habitat by identifying the depth at which 6 mg.L-1 oxygen occurs at the end-of-summer stratification period. Then we develop a new model to predict the 10 degreesC depth or upper habitat boundary for the same date. These two boundaries can be used in conjunction with measured individual strata volumes to calculate the optimal habitat volume. Parameters needed for the models include lake morphometry, total phosphorus (TP) concentration, and Secchi depth or dissolved organic carbon (DOC) concentration. Thus, the optimal habitat model can be used to predict the effects on optimal habitat volumes of changes in trophic status (increases or decreases in TP), or changes in light transmission (caused by changes in DOC or its surrogate in these lakes, i.e., Secchi depth) that result from changes in climate, land use, acid-base status, or incident ultraviolet radiation levels.