Differences in migration pattern and growth of polish and finnish sea trout (Salmo trutta L.) released in the same areas

Abstract

Tagged sea trout (Salmo trutta) from the Vistula (Poland) and Isojoki (Finland) rivers were released into the Vistula River mouth and into the Gulf of Finland outside of the city of Helsinki. Vistula sea trout released into the Vistula River mouth were less frequently caught (75%) in and nearby the place of their release than were Isojoki sea trout released in the same place (92.3%). Finnish sea trout seldom migrated to the southern Baltic Proper. Of the Isojoki sea trout released into the Gulf of Finland, 74.1% were caught in the Gulf of Finland. The behavior of the two stocks released into the Gulf of Finland could not be compared due to the low tag returns of the Vistula stock. Isojoki sea trout released into the Vistula River mouth attained a total length of 49 cm and a body weight of 1.7 kg by the end of the first year after release, and 63 cm and 2.8 kg by end of the second year; while those released into the Gulf of Finland attained 39 cm and 654 g by the end of the first year, and 52 cm and 1.6 kg by the end of the second. The results of stocking was low; between 0.2 and 160.3 kg per 1000 smolts, and depended on the method of fish tagging, smolt quality, and stocking site.