Measuring the Seasonal Supply of Habitat Space for Fishes in Lakes

An empirical seasonal temperature model (STM) for dimictic lakes is demonstrated. The model is an extension of the late summer profile model developed by Mackenzie-Grieve and Post (CJFAS 63:788-797 2006). Temperature profiles over the stratified period are described using eight parameters: the Julian dates for the start and end of stratification and when the surface temperature peaks; the minimum hypolimnion and peak surface temperatures; and the depth development (two parameters) and steepness of the thermocline. The model is fitted using nonlinear least squares. Sample datasets fit very well and model parameter estimates are consistent with predictions of previous parameter-specific models. When the STM model is linked to a lake's hypsometric curve and a temperature suitability model for a target fish species, the habitat volume space over the period of stratification can be computed. The impacts of climate warming can be assessed by adjusting some of the model parameters; increasing surface temperatures are accompanied by a proportional lengthening of the period of stratification. This empirical temperature model provides a simpler alternative to the data- and computer-intensive physics-based models.