Bioenergetics Modeling of Stream Trout Growth: Temperature and Food Consumption Effects

Abstract

We investigated bioenergetics modeling of growth as an approach for assessing the effects of temperature changes on stream dwelling rainbow trout Oncorhynchus mykiss. Study objectives were (1) to determine the relative effect of temperature versus food consumption on model-predicted growth and (2) to identify relationships between model-predicted food consumption and commonly measured environmental variables. A bioenergetics model for rainbow trout was calibrated to apparent age-1 growth in summer and fall–spring periods for 10 years at eight Sierra Nevada, California, study sites. Model analyses showed that the observed year-to-year variation in summer growth was related to food consumption but not to temperature and that temperature was more important, but still of secondary importance, to observed variation in fall–spring growth. Growth at all sampling sites appeared lower and more variable in summer than in other seasons, and variation among sites and years in the food consumption parameter P (determined by fitting the model to observed apparent growth) was highly related to environmental variables during fall–spring but not during summer. During fall–spring, 80% of the variation in P was explained by a linear regression model that included temperature, flow, and trout density. Summer P-values were only weakly related to stream gradient. Our data and analysis indicate that (1) when not extreme, temperatures in summer may have less effect on growth than during other seasons and (2) growth is more affected by factors controlling food consumption (including indirect effects of temperature) than by the direct effects of temperature.