Do spatial models of growth rate potential reflect fish growth in a heterogeneous environment? A comparison of model results

Spatial models of fish growth rate potential have been used to characterize a variety of environments including estuaries, the North American Great La kes, small lakes and rivers. Growth rate potential models capture a snapsho t of the environment but do not include the effects of habitat selection or competition for food in their measures of environment quality. Here, we te st the ability of spatial models of fish growth rate potential to describe the quality of an environment for a fish population in which individual fis h may select habitats and local competition may affect pet capita intake. W e compare growth rate potential measurements to simulated fish growth and d istributions of model fish from a spatially explicit individual-based model of fish foraging in the same model environment. We base the model environm ent on data from Lake Ontario and base the model fish population on alewife in the lake. The results from a simulation experiment show that changes in the model environment that caused changes in the average growth rate poten tial correlated extremely highly (r(2)greater than or equal to0.97) with ch anges in simulated fish growth. Unfortunately, growth rate potential was no t a reliable quantitative predictor of simulated fish growth nor of the fis h spatial distribution. The inability of the growth rate potential model to quantitatively predict simulated fish growth and fish distributions result s from the fact that growth rate potential does not consider the effects of habitat selection or of competition on fish growth or distribution, proces ses that operate in our individual-based model and presumably also operate in nature. The results, however, do support the use of growth rate potentia l models to describe the relative quality of habitats and environments for fish populations.