Predicting juvenile salmonid drift-feeding habitat quality using a three-dimensional hydraulic-bioenergetic model

Abstract

This paper describes a physically based three-dimensional bioenergetic model for prediction of physical habitat quality for drift-feeding juvenile salmonids in a river. A three-dimensional Computational Fluid Dynamics (3D-CFD) model is used to simulate hydraulic patterns in a 50 m reach of the Bere stream, Dorset, UK. This information is then combined with a bioenergetic model that uses behavioural and physiological relationships to quantify the spatial pattern of energy gain when drift feeding. The model was tested by comparing patterns of predicted energy intake with observed habitat use by juvenile salmonids at different times of day. Hydraulic measurements or predictions are required as input to bioenergetic models to calculate the foraging range of the fish. Horizontal and vertical velocity gradients can be high and variable in shallow streams with complex topography and roughness zones. In this paper, a three-dimensional hydraulic model enables more realistic calculation of the foraging area of the fish. This takes account of the complexity of horizontal and vertical velocity gradients. Numerical experiments are used to demonstrate the sensitivity of energetic gain to changes in the method of calculating foraging area. Results support the hypothesis that feeding fish preferentially select areas of high energy gain, but move to areas of lower velocity when resting.