APPLICATION OF A FRY (O+) ABUNDANCE INDEX, BASED ON SEMIQUANTITATIVE ELECTROFISHING, TO PREDICT ATLANTIC SALMON SMOLT RUNS IN THE RIVER BUSH, NORTHERN-IRELAND

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 smelt numbers migrating through a downstream trap in subsequent years (r(2)=0.716, P<0.001), suggesting a high degree of predictive ability. This predictive ability decreased as smelt age increased, suggesting influence of density-independent mortality. Potential application of the technique to estimate smelt production from rivers having no trapping facilities is discussed, together with sources of variability potentially affecting estimates. (C) 1995 The Fisheries Society of the British Isles