<論文>北海道古宇川におけるアメマスSalvelinus leucomaenisの齢別成熟比率  [in Japanese] <Orignal>Age-specific maturation ratio of white-spotted charr Salvelinus leucomaenis in Furuu River in Hokkaido  [in Japanese]

The variation in the weight of individuals with same age and the age-specific maturation ratio of white-spotted charr Salvelinus leucomaenis are examined in Furuu River in Hokkaido. The variance in the age-specific weight is extremely high and the strong intraspecific competition is expected to occur in the population. The maturation ratio of females in the stream is zero at any age and that of males in the river ranges from about 21 % to 58 % depending on age. It is shown that (1) it is a rare event for females to mature in the river, (2) the proportion of maturing in the river is about 21 % in males with 2+ age and (3) there is a possibility that both males and females with 5+ age in the river migrate to the sea. (4) about 25 % of sea-run individuals are immature.