In rivers and streams construction of dams often lead to fragmentation of fish populations since dams can reduce or prevent fish migration both up- and downstream. Such fragmentation will lead to loss of gene flow between upstream and downstream populations, creating more or less genetic isolated populations. In Lilleelv, a medium sized stream running into the large Nidelva river in Arendal, a dam established around 100 years ago has acted as a permanent barrier for sea trout (Salmo trutta trutta) trying to migrate up to spawn. Sea trout is every year observed in the deep pool below the dam, seemingly wanting to migrate up river, but the dam has for the last 100 years prevented this from happening. It is believed that sea trout was using this stream as spawning grounds before the dam was established. A stationary brown trout population is now present in the upstream part of the river now, and the brown trout and the sea trout has been isolated for the last 100 years.
Now, a fish ladder system along this dam is being constructed and this will re-open the stream for migrating sea trout and thus leading to a breakdown of the reproductive barrier between upstream brown trout and downstream sea trout populations. These circumstances provide the opportunity to study the effects of a unique “natural experiment”, where the changes in gene flow most likely will affect the micro-evolutionary processes in these populations. We are interested in how the re-establishment of the sea trout in this stream will affect the stream as a whole? Together with researchers from the Institute of Marine Research in Arendal and The Norwegian Institute for Water Research (NIVA) in Grimstad we are planning to monitor the effect of the re-opening on the stream ecosystem, including the trout populations, the river bed invertebrate community and the river bed gravel structure. Several student projects are available and will include field work and statistical analysis of data.
|Virksomhet:||Universitetet i Agder|
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