Variation in the time of spawning of Atlantic salmon (Salmo salar) and its relationship to temperature in the Aberdeenshire Dee, Scotland

Time of spawning of Atlantic salmon (Salmo salar) in the River Dee in northeast Scotland was assessed from cumulative counts of redds made in five areas of the river system. Spawning occurred earliest at high altitude sites in the upper reaches of the river and progressively later at sites further downstream. The period of spawning at each location varied between 18 and 48 days and was more protracted at low altitude sites. Hatch occurred earlier in ova from redds in the lower altitude sites. Differences in the timing of spawning and hatch are considered in relation to water temperature. It is suggested that variation in the time of spawning is of adaptive significance and that it relates to the optimal timing of fry emergence in different parts of the river system.