Ice cover and spatial distribution of trout (Salmo trutta) in a small stream

Sammanfattning: Winter has been generally considered as a bottleneck period for salmonid populations, but recent studies show it might be more context related. The purpose of this study was to examine how surface ice changes spatial distribution of juvenile one-year-old brown trout in a small boreal stream. I hypothesized that the presence of surface ice will allow a more even distribution of trout over the entire width of the stream while in the absence of ice, trout will be more heavily associated with near-edge habitats. I also hypothesized trout will be more evenly dispersed at night over the width of the stream even in the absence of surface ice. My results show a strong positive correlation between icecover and spatial distribution. In the presence of surface ice trout use the whole width of the stream, while in the absence of ice the middle regions of the stream were almost completely devoid of fish. My results also show there was no difference in the spatial distribution between night and day in the presence of ice cover, but in the absence of ice cover trout were more tightly associated with the stream edge during day whereas at night they were more evenly dispersed over the entire width of thestream.