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Generally, the size of a sea trout population is under the influence of a number of ‘bottlenecks’ in the life cycle. Reduced spawning- and nursery habitat, as a consequence of sand walk and adjustments of streams, is one of the major obstacles. Another important factor is obstacles in connection with migration. A very important obstacle during migration is the passage of dams which deny the fish access to important habitats, both when it comes to downstream and upstream migration. The dams’ negative effect on the population of migrating fish is well-documented (Aarestrup et al. 2003; Aarestrup et al. 2006a, b, c; Baktoft et al. 2007). It has lead to a number of model reflections on the impact on the fish stock if the dam are removed (Olesen & Aarestrup 2006). However this model has not been validated. The possibility of such a validation now exists in the River Villestrup, where the original model was developed. In this comprehensive restoration project, the plan is to remove all the dams in the main stream. This gives a unique chance to test the size in the stock of migrating fish before and after the removal of the dams. The study aims at estimating the spring run of smolt and kelts in a number of defined years before and after the removal of the dam. The run has been estimated in 2008 and 2009 before weirs where removed. The trapping operations gave an estimated smolt run of 4500 and 6500 smolt migrating into Mariager Fiord, respectively. The restoration project will be finished in 2011 and estimation of the run should be repeated in 2013-2015. The project provides us with valuable information on the potential for optimizing the fish stocks without releases.

The project is running concurrently with project 38258 “The marine life and survival of sea trout” and with the EU funded project 38872 “Living North Sea” (LNS). LNS is a 15 partner interregional management project with the specific aim to focus on specific issues and potential solutions for fish migration.


  • Research area: Freshwater Fisheries and Ecology
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ID: 2286709