Predicting salmonid population ecology from individual fish responses to environmental changes: bridging behaviour, conservation and fisheries management.

Abstract

Current habitat-association models used in the management of the socio-economically and ecologically important chalk stream salmonid populations fail to incorporate fish behaviour and the interactions between fish with their environment and this limits their ability predicting management-relevant salmonid population responses to environmental change. A salmonid individual-based model is parameterised to predict fish distributions and growth as the modelling approach address the weaknesses of current models. Virtual forager parameters are derived from published investigations and models of salmonid behaviour and bioenergetics. Data from three field studies at the same chalk stream site are used to describe the environment and initial fish population with subsequent data on fish population patterns used to statistically validate the IBM. I found that current recommendations for population enhancement may be futile beyond a threshold population density and regimes that address habitat quality should be adopted. Potential parasite impacts are investigated theoretically by simulations on the mode of impact on their host and identify the most population damaging parasites as those with high effect on host physiology. The management of salmonid predators in fisheries is predicted to have little benefit to salmonid growth and should not be implemented. Additionally, the removal of the dominant aquatic macrophyte for flood risk management is potentially damaging to salmonid populations and recommendations for a sympathetic design are provided. The model described here can be used to produce robust predictions of salmonid population patterns in riverine habitat and allows users to test the impact of environmental change on salmonids to be used for proactive management in light of current rates of environmental change.