Migration to the sea of river spawning whitefish (Coregonus lavaretus L.) fry in the northern Baltic Sea
Jokikokko, E.; Huhmarniem, A.; Leskelä, A.; Vähä, V.
The migration of river spawning whitefish was studied in the Simojoki and Tornionjoki Rivers in spring 2005–2008 using a rotary smolt screw. In the Simojoki River, the study started well before the whitefish fry migrated, but it had to be stopped soon after the peak of migration. In the Tornionjoki River, the fry migration started before the screw was in place, but it was possible to follow the latter part of the migration. Dipnetting showed that whitefish larvae were present on the shores of both rivers soon after hatching, but the migrations did not start until after mid-June, when the fry were about 30 mm long. The migrations peaked in late June–early July and the number of fry decreased rapidly thereafter. In the Tornionjoki River, they were caught daily until early September, when the screw was removed. The growth of whitefish fry seemed to be similar in both rivers.