摘要：During the breeding seasons of 1998–2001, the spawning migration of stream-dwelling Dolly Varden (Salvelinus malma) was investigated in four small spring-fed tributaries of the Shiisorapuchi River, Hokkaido, Japan. From late September to late October, Dolly Varden continuously migrated into these tributaries from the mainstream without any clear peaks. Precipitation was positively correlated (P < 0.05) with the number of migrants in two tributaries, but not in the other two. No clear relationship was observed between the number of migrants and the water temperature for either the mainstream or the tributaries. Nocturnal migration behavior was recognized in one tributary, but it was diurnal in two tributaries, and there was no clear tendency in the other. Body size of migrating Dolly Varden was not correlated with the entry date for either sex. No significant difference in the entry date was observed between males and females for any tributary or for any year. However, the number of males entering a tributary was positively (P < 0.05) correlated with that of females, indicating a synchronous migration of males and females. Because the number of females was not correlated with any environmental factor, we suggest that male Dolly Varden migrate into tributaries following mature females, possibly via pheromonal stimuli.
