RECAPTURE, GROWTH AND MOVEMENT OF WILD, POND- AND HATCHERY-REARED EUROPEAN GRAYLING (THYMALLUS THYMALLUS L.) RELEASED IN A SMALL STREAM

摘要

European grayling (Thymallus thymallus L.) is a native species to the Czech Republic (Lusk 1975). In streams of the Czech Republic it has been decreasing for many years. To compensate losses in wild populations, stocking of hatchery- and pond-reared graylings has become a common practice. In Northern Europe and North America the efficacy of grayling stocking to lakes and streams has rarely been examined (Carlstein and Eriksson 1996). Stocking of grayling in running waters has not been successful (Kaya 1990). A number of studies were performed in a seminatural river in Sweden to examine the reasons for the extensive dispersal of grayling and to gain knowledge of post-stocking behaviour of 1- and 2-years-old European grayling. The origin of the stocked grayling (Carlstein and Eriksson 1996) did not influence downstream dispersal to any significant degree. In this study growth and survival of stocked grayling was compared with that of the 1+ resident grayling present in the experimental stretches.