External Organisations

  • Lund University, Sweden
  • Municipality of Viborg, Denmark

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In many shallow lakes cyprinid fishes like roach (Rutilus rutilus) and bream (Abramis brama) aggregate in inlet- and outlet streams during winter. Since 2005 DTU Aqua has investigated these seasonal migrations of cyprinids in three lakes and thereby furthered our knowledge on the behavior of some of the most common fish species in Denmark. Up to 85 % the bream and roach may leave the lake and individuals may stay out of the lake for periods up to 7 months during winter. However the part of the population that participates in this so called partial migration varies between years. We therefore continue this investigation for the next three years in order to increase the length of the time series leading to a better understanding of the annual variation in migration patterns. Moreover, we seek to solve several specific research questions related to partial migration of cyprinids. This project will increase our knowledge on fish behavior and fish population dynamics in lakes and thereby expand our tool box for management of lacustrine fishes.

1) How does cyprinid partial migration influence top-predator pike feeding dynamics?
Pike feeding patterns and prey availability in a number of open and closed lakes are monitored from early fall to late spring. This could reveal that pike in open lakes where prey abundance fluctuate during season require more management attention i.e. due to restricted growth and/or increased cannibalism in periods with low prey abundance.

2) Migration between neighboring lakes
Two of the three focal lakes in which we are monitoring seasonal migrations are situated only 3 km apart and connected by a small stream. So far it has become obvious that from time to time large amounts of fish switch from one lake to another. By continuing to pit tag and monitor fish migration we are likely to observe more of these mass migration events, which in turn facilitate a better understanding of why and when these mass migrations occur. Clearly, the level of exchange between neighboring lakes is an important factor to consider when it comes to management of lakes.

3) Cost effective biomanipulation
The European Water Framework Directive implies that the water quality in many Danish lakes needs to be improved in the future. One method to obtain such improved water quality is biomanipulation, i.e. removal of large amounts of benthivorous- and planktivorous fish from the lake. This part of the project evaluates if cost effective biomanipulation can be done during winter by removing fish from the inlets and outlets.

The project is coordinated by DTU Aqua.



  • Research area: Freshwater Fisheries and Ecology & Observation Technology
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ID: 2286875