Population size in stream‐living juveniles of lake‐migratory brown troutSalmo truttaL.: the importance of stream discharge and temperature

Based on the analysis of 17 successive year‐classes, this investigation attempted to identify the factors determining year‐to‐year variation in population size of the stream‐living juveniles of Lake Hald‐dwelling brown troutSalmo truttaL. Population size appeared to be influenced chiefly by annual recruitment that in turn, was determined by stream discharge and temperature. These patterns matched those previously highlighted for a resident population located >2500 km apart and emphasised the importance of environmental (climatic) variability as a major regulating agent of population size in stream brown trout. However, distinctly shaped recruitment–discharge relationships between the two populations suggested different mechanisms in response to environmental variability and thus to persist in time.