Size-related differences in behaviour and spatial distribution of juvenile Atlantic salmon in a novel environment

Abstract

Within a month of first feeding sibling juvenile salmon had developed not only large differences in size (up to fivefold in weight), but also significant differences in behaviour. Large fish remained in refuges (overhead cover) significantly longer after having been frightened. On leaving the shelters most small fish established individual territories on the bottom and. downstream of the shelters. The greater aggressiveness of small fish in a novel environment (from holding tank to experimental stream) was related to this apparent territoriality. The increased shelter residence time and delayed establishment of individual territories might be interpreted as greater caution in large fish, which are able to avoid risky situations due to their higher energy reserves. In contrast, smaller fish need to leave refuges more quickly and to establish individual territories in a novel environment.