Transferability of habitat preference criteria for larval European grayling (<i>Thymallus thymallus</i>)

Abstract

We examined the transferability of habitat preference criteria for larval European grayling (Thymallus thymallus) to two rivers in Finland by testing whether there were significant positive rank correlations between local fish densities (shoals per square metre) and preference indices for depth, velocity, substrate, and vegetation cover or selected combinations. Two sets of preference curves, one obtained from literature for the River Pollon, France, and another for the River Kuusinkijoki, Finland, were tested. All transferability tests for water velocity criteria were successful, correlation coefficients between local fish densities and preference indices ranging from 0.83 to 0.92. Criteria for depth and substrate transferred inconsistently, and criteria for vegetation cover failed to transfer to either target site. Combined indices predicted fish microdistributions inconsistently and they never performed better than the best univariate index for each site. Our results suggest that universal preference criteria for water velocity may exist for larval grayling and that it may be best to use these criteria alone in habitat hydraulic modelling when predicting habitat suitability to larval grayling.