Population Regulation in Contrasting Populations of Trout Salmo trutta in Two Lake District Streams

Abstract

(1) The chief objective was to compare the population dynamics of Salmo trutta L. in Wilfin Beck, populated only by resident brown trout, and in Black Brows Beck which serves as a nursery for the progeny of migratory trout (a mixture of sea and estuarine trout). (2) Survivor density and loss-rates at different stages in the life cycle were strongly 'density-dependent' on egg density in Black Brows Beck, but simple proportionate survival occurred in Wilfin Beck and loss-rates were more constant than those in Black Brows Beck. (3) Key-factor analysis showed that population density in Black Brows Beck was regulated by density-dependent survival in the early stages of the life cycle, and that there was no evidence for similar density-dependent regulation of the trout population in Wilfin Beck.