Application of a fry (0+;) abundance index, based on semi‐quantitative electrofishing, to predict Atlantic salmon smolt runs in the River Bush, Northern Ireland

Abstract

An abundance index for 0+ Atlantic salmon was based on semi‐quantitative electrofishing estimates at 137 sites in typical juvenile habitat throughout the River Bush (N. Ireland). 0 + abundance was linearly related to total smolt numbers migrating through a downstream trap in subsequent years (r2= 0.716, P<0.001), suggesting a high degree of predictive ability. This predictive ability decreased as smolt age increased, suggesting influence of density‐independent mortality. Potential application of the technique to estimate smolt production from rivers having no trapping facilities is discussed, together with sources of variability potentially affecting estimates.