The autumn and spring emigrations of juvenile Atlantic salmon, Salmo salar L., from the Girnock Burn, Aberdeenshire, Scotland: environmental release of migration



Peaks in the emigratory activity of sexually immature, juvenile Atlantic salmon, Salmo salar, occur in autumn and early winter and in spring at the Girnock Burn in Aberdeenshire. Stream temperature is apparently without effect on the release of potentially emigrant fish from the stream. Migrants tend to leave the stream when stream discharge rate is elevated. Whereas downstream movements in autumn and the earlier part of the spring are made almost invariably when the stream's discharge rate is higher than the seasonal norm, later in spring they often occur when discharge rates are lower than the seasonal norm and when no apparent increase in absolute stream discharge rate has occurred. Emigration is depressed in the lunar quarter centred on the full moon. The nature of the relationship between the autumn and spring emigrations is discussed.