PREDICTING HABITAT SUITABILITY FOR LOTIC FISH - LINKING STATISTICAL HYDRAULIC MODELS WITH MULTIVARIATE HABITAT USE MODELS

Quantitative estimates of habitat suitability in a stream reach genera lly result from coupling a hydraulic habitat model with a biological m odel of habitat use. The choice of each of these models has led to muc h controversy and discussion. Nevertheless, most habitat studies of lo tic fish use a deterministic hydraulic model and univariate suitabilit y curves. The objective of this contribution is to present a new, alte rnative method, which relates statistical hydraulic models to multivar iate habitat use models. Our statistical hydraulic models predict the frequency distributions of hydraulic variables such as velocity or wat er depth within stream reaches. Their main advantage is the simplicity of their input variables (mainly discharge and average characteristic s of the reach). Our multivariate formulation of habitat use models ta kes into account the local variability of fish habitat, predicting hab itat suitability as a function of the frequency distribution of hydrau lic variables within the local fish habitat. We demonstrate how these two model types can be linked to estimate habitat suitability in a str eam reach as a function of discharge, focusing on two fish species (ba rbel, chub) in a regulated reach of the French Rhone River. The main l imitations of this new method are a result of mathematical constraints associated with the linkage of the two modelling approaches and to un certainties in transferring biological models from one stream to anoth er because of insufficient data. Despite these limitations, the method provides solutions to several critical problems facing existing appro aches and the simplicity of its input variables can accelerate the val idation process of habitat models. Therefore, our first simulations st rongly encourage: (i) the use of statistical approaches to describe hy draulic variables; and (ii) the study of multivariate habitat use mode ls that apply to a large variety of streams. (C) 1998 John Wiley & Son s, Ltd.