Smolt age and size of Atlantic salmon Salmo salar L. and sea trout Salmo trutta L. in a Norwegian river

Abstract

This paper gives data on smolt age and length of Atlantic salmon and sea trout in the Orkla river in the period 1979 - 1981. The smolt age of the salmon was significantly higher in 1979 (4.1 years) as opposed to 3.4 and 3.3 years in 1980 and 1981, respectively. However, the average length of the salmon smolts did not differ during the study period. Sea trout smolts showed a significantly lower average length in 1979 compared to that found in the two preceding years. No such difference could be detected in the smolt age which ranged between 3.3 - 3.6 years during the study period. Smolts of both species showed a heterogeneous length distribution with a variation between 100 - 170 mm for salmon and 110 - 200 mm for sea trout. It is concluded that growth rate is more important than the mere attainment of a critical length for initiating smolt descent.