Size, growth, population density and food of brown trout Salmo trutta L. in two sections of a south Swedish stream

Abstract

Size, growth and population density of trout, Salmo trutta populations between the upper part of a small stream and downstream section were compared. The density of 0+ trout was about equal in the two sections, while trout >0+ were more numerous in the downstream section. Apart from water depth and volume, abiotic conditions were similar in the two sections. The utilization by trout of the available benthos was always greater in the downstream section. The discrepancies found in trout size and density between the sections were considered to be due to the increased spatial requirements by the larger fish. Growth rate of 0+ fish in terms of length increase per month was the same in both sections. The 0+ fish were found in the upper section. Earlier hatching due to temperature differences between the sections and larger size at hatching in the downstream section were factors of possible significance.