Habitat evaluation as a fisheries management tool

Abstract

The application, rationale and process of habitat evaluation methods are discussed in the context of present day fisheries management. The need to consider habitat features at site and catchment level is stressed. Development of habitat evaluation techniques for assessing brown trout habitat in Welsh streams is reported, and examples of these approaches are given: qualitative (visual assessment), semi‐quantitative (a combination of subjective and quantitative measurements) and quantitative (measurements on transect system). Habitat attribute‐fish population models were based on functional linear regressions and multiple regression (for the quantitative method). Quantitative models explained up to 80% of the variance in abundance of medium sized (10–20 cm) trout in hard water (>25mgl ‐1 CaCO 3 ), but were less effective when data from soft waters were included. Testing of the qualitative and semi‐quantitative methods on independent data demonstrated that the latter was more effective in predicting habitat quality. Survey costs varied considerably but, although the more precise methods were more costly per site, they were the most cost‐effective because fewer sites were required for a given level of precision. The problems associated with soft‐water sites are discussed in terms of factors affecting site carrying capacity; and selection of methods is briefly considered in the light of current management practise.