Birdpredation, fish behavior and fish movements between lakes (38266)

This project supports several of the sections research activities including fish migration, predator-prey dynamics and habitat restoration activities. In many shallow lakes cyprinid fishes like roach (Rutilus rutilus) and bream (Abramis brama) aggregate in inlet- and outlet streams during winter. 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, there is interannual variation in the part of the population that participates in this so called partial migration.

Since 2005 DTU Aqua has investigated patterns of seasonal migrations of cyprinids in three Danish lakes and thereby, in combination with international collaborators, furthered our knowledge on the behavior of some of the most common inland fish species in Denmark and Europe. This has resulted in numerous publications/reviews about partial migration and other aspects related to seasonal movements of lacustrine fish. 

Currently, focus is on furthering our understanding of the reasons behind movement patterns between adjacent 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 move 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 fish exchange between neighboring lakes is an important factor to consider when it comes to management of lakes not least when it comes to lake restoration measures by fish removal, which may be pointless if extensive emigrations from neighboring lakes occur following fish removals. In relation to this we also explore how knowledge about migration and movement patterns of cyprinid fish, a common target in biomanipulation measures in North European lakes, can be used to optimize future biomanipulation attempts. 

In addition, a part of the project focus on exploring patterns of avian predation on lake fish, Here we take advantage of the PIT tag technology that we otherwise use to monitor fish inter-lake migration behavior in the project. By scanning areas that birds use for roosting and nesting for PIT tags, we can obtain estimates of seasonal and interannual variation in avian predation on lacustrine fish.

Overall, this project increases our knowledge on fish behavior and fish population dynamics in lakes and thereby expands our tool box for management of lacustrine fishes. 

Partners
National Institute of Aquatic Resources, DTU Aqua (coordinator)
Viborg Municipality, Denmark
Lund University, Sweden
Swiss Federal Institute of Aquatic Science and Technology, Switzerland

Funding
The project is funded by the Danish Rod and Net Fishing License Funds.

Research area: Freshwater Fisheries and Ecology