Post‐stocking dispersal of European grayling, Thymallus thymallus (L.), in a semi‐natural experimental stream

Abstract

Abstract Artificially hatched and reared juvenile European grayling, Thymallus thymallus (L.), from three natural populations were released into an experimental stream. Two of the populations were from lakes and the third population was from a river. Post‐stocking dispersal was studied by recapturing fish in traps and by electric fishing after each of the stocking exercises. On all three occasions the first fish to be recaptured were caught in a trap about 400 m downstream from the release site, within 5–12 min of release. Proportions of stocked grayling juveniles recaptured by electric fishing in the fast‐flowing section of the experimental stream (the rapids) were 9.9%, 46.7% and 16.6% after the first, second and third stocking, respectively. No significant population‐specific difference was found between fish caught in the downstream trap and fish recaptured in the rapids. The uppermost part of the rapids (stretch 1) and the catch in the upstream trap was dominated by fish of riverine origin. Post‐stocking migration was influenced by sex but not by body size. Females showed a greater propensity to stay in the rapids compared with males. Implications of the results for stocking grayling in natural streams and regulated rivers are discussed.