Session D2: Conservation of a Landlocked Salmonid Population in a Regulated River: Taking a Holistic Approach

Abstract: The regulated River Klarälven hosts an endemic population of landlocked Atlantic salmon (Salmo salar). During the 1960s the population reached an all-time low, and extensive stocking, trapping and transportation of spawners past eight dams, together with a no-fishing policy in the lake, has led to an increase in the population. In an attempt to further improve the situation for this landlocked population, we have taken a holistic approach in evaluating where further measures are needed. Hence, we have measured trap efficiency for upstream migrating spawners at the lowermost dam, spawning success, overwinter survival of post-spawners, downstream passage success of smolts and kelts and smolt production. Here, I present an overview of our eight years of research in the River Klarälven, focusing on trap efficiency for upstream migrating spawners and smolt prodution. Trap efficiency varied from 18-78%, depending on river discharge and experience of the fish. Estimates of smolt numbers, based on mark-recapture studies, were difficult to obtain in high flow conditions, and our best estimates revealed a minimum smolt run of approximately 4,000 in one year and 20,000 in a subsequent year. A simple population model was developed for the River Klarälven, where we used our own data and data from the literature to estimate the number of return spawners. We found that the model predictions did not match well with the observed return rates. We believe that this discrepancy is related to the difficulties in estimating smolt production and downstream passage success in large rivers with highly variable discharge regimes.
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