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Inter-annual variation in the seaward migration of diadromous fishes in relation to meteorological anomalies, with a view to seasonal forecasting

European eels (Anguilla anguilla), anadromous brown trout (Salmo trutta) and Atlantic salmon (Salmo salar) undergo seaward migration following a seasonal physiological transition in preparation for marine survival. We used daily count data from a catchment in the west of Ireland to explore the extent to which inter-annual variation in seaward migration timing during the past half-century has reflected local seasonal meteorological anomalies and long term climate trends. For each species, we quantified four migration timing anomalies relative to a moving average central migration window (early, late, bimodal and condensed) and identified associations between environmental and phenological anomalies by multinomial logistic regression. We found that migration phenology of all three species is advancing and associations between seasonal environmental anomalies and inter-annual variability in migration phenology is pronounced in Atlantic salmon smolts. Prediction of Atlantic salmon smolt migration anomalies is limited by uncertainties in seasonal forecasts produced for the west of Ireland.