Life History Patterns of Freshwater Resident and Sea-Run Migrant Brown Trout in Norway

Abstract

Brown trout Salmo trutta in Vangsvatnet Lake, Norway, include freshwater residents that mature sexually without any sea run and migrants that smoltify and migrate between fresh water and the sea one or more years before maturing. Migrants leave Vangsvatnet Lake during spring and move in coastal waters up to 100 km from the lake outlet before they return to their home river in summer or autumn; older migrants return earlier than younger migrants, sexually mature fish before immatures. Both residents and migrants spawn together in tributaries to Vangsvatnet Lake. Young brown trout (parr) grow in the tributaries and lake; lake dwellers grow faster than stream dwellers. Parr that become migrants at age 2 grow faster than parr that become residents, but parr that become migrants at age 4 and older grow more slowly than those that become residents. Parr that smoltify or mature at a young age grow faster than parr that do so later. Resident males are 2–8 years of age, and 13–47 cm in tip length, resident females 3–10 years and 21–45 cm. Smolts are 2–7 years old and 14–29 cm long. Mature migrants are 3–9 years old; males are 29–67 cm and females 34–67 cm long. Sex-ratios were in favor of males among residents, in favor of females among migrants. Received October 14, 1983 Accepted November 14, 1984