THE RELATIONSHIP BETWEEN A SUMMER FRY (0+) ABUNDANCE INDEX, DERIVED FROM SEMI-QUANTITATIVE ELECTROFISHING, AND EGG DEPOSITION OF ATLANTIC SALMON, IN THE RIVER BUSH, NORTHERN IRELAND

摘要

Atlantic salmon survival in the R. Bush (N. Ireland) from egg to summer 0+ was inversely density-dependent on egg deposition (P<0.05). A stock-recruitment relationship derived from egg deposition and summer 0+ abundance index data was compared to that derived from adult and smelt counts based on total trapping. Fitted Ricker curves indicated maximum recruitment at around 2.35 million eggs and 2.46 million eggs for 0+ index and smelt count methods, respectively. Salmon 0+ abundance index data from semiquantitative electrofishing could be obtained with relatively little effort, and used to derive whole-river stock-recruitment relationships on rivers where only: adult count or some other estimator of parental stock is available. The derivation and expression of spawning targets from stock/recruitment relationships is discussed with reference to the R. Bush data.