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Partial migration in fresh water fish

Each year as winter draws in and the water temperature decreases in Lake Krankesjön in southern Sweden, huge numbers of fish, predominantly roach (Rutilus rutilus), migrate out of the lake and up the streams. However, only part of the population migrates; many fish remain in the lake for the entire winter, which is puzzling. Why do some individuals stay and some go?

Each year as winter draws in and the water temperature decreases in Lake Krankesjön in southern Sweden, huge numbers of fish, predominantly roach (Rutilus rutilus), migrate out of the lake and up the streams. However, only part of the population migrates; many fish remain in the lake for the entire winter, which is puzzling. Why do some individuals stay and some go?

Key personality traits

Researchers fishing

To test the idea of animal personality we will quantifiy a key personality trait (boldness). Individuals will be ‘tagged’ with a Passive Integrated Transponder (PIT-tag) which, when activated by receivers placed strategically across the three inlet and outlet streams will tell us who is migrating and when. We will also have information on the choice of stream, how long migrants spend in the streams and the overwinter survival of each migratory roach.

Variation of body shape

Tagging fish
Photo: Ben Chapman

We noticed a great deal of variation in body shape in the roach we caught, from relatively deep-bodied fish to shallow-bodied, fusiform fish, so we’ll also investigate the role of body shape using geometric morphometric analyses. Finally we have length and weight measurements for all of the fish in our study, which will help us to assess the importance of individual condition in migratory tendency in roach. Here, PIT-tag next to roach.

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Centre for Animal Movement Research
Evolutionary Ecology, Department of Biology
Ecology building S-223 62 Lund Sweden