Estimating sampling bias when using electrofishing to catch stone loach

Point abundance sampling, using electrofishing, for stone loach Barbatula barbatula in two habitats, riffle and pool, showed that there was no difference in density between the two habitats. The density of fish increased significantly (1·8 fold; P < 0·001) when the substratum of small cobbles (128–256 mm) was removed and electrofishing repeated.