SUITABILITY INDEXES FOR JUVENILE O-RUTILUS (L)] USING POINT ABUNDANCESAMPLING DATA( ROACH [RUTILUS)

A habitat suitability model is derived for juvenile 0 + roach [Rutilus rutilus (L.)] in the river Great Ouse (UK) using data collected by po int abundance sampling by electrofishing. A total of 1718 point sample s was used in the analysis. Of these, 392 contained juvenile roach. Po lynomial equations describing habitat suitability are derived from dep th, mean substratum particle diameter and water velocity data, and an index of plant cover suitability is described. Optimum conditions for roach are a depth of 1 m with a coarse (particle diameter 15-20 mm) su bstratum and negligible velocity, in the presence of floating and subm erged broadleaved plant cover. The model is capable of discerning betw een null (fish absent) and non-null (fish present) points in the origi nal data set. It is shown that sampling effort may be reduced by appro ximately 60% without altering the model's predictions.