GROWTH AND SEX DISTRIBUTION IN AN ANADROMOUS POPULATION OF ARCTIC CHAR IN NORTHERN NORWAY

Presmolt Arctic char Salvelinus alpinus in the River Halselva watershe d, northern Norway, were analysed with respect to growth and sex distr ibution. Two main hypotheses were tested: (1) females dominate among t he first-time sea migrants; and (2) age at smoltification depends on p resmolt growth rate. Our results showed no significant difference in s ex distribution of first-time migrants. There was a low frequency of e arly maturing males in the population, and no differences between the sexes with respect to early sexual maturation were observed. The first -time sea migrants showed a higher presmolt growth rate than the nonmi grating parr in Lake Storvatn, the only take of the Halselva watershed . Based on both the low frequency of mature parr and the sex ratio in the smolt run, the population of Arctic char in the profundal zone in Lake Storvatn is predominantly anadromous fish. These fish migrate to sea at a greater age than the first-time migrants observed in the Rive r Halselva and are thus ''temporarily'' resident. This differs from ot her northern Arctic char populations, in which permanent freshwater-re sident fish often constitute the predominant part of the population.