Management of the fish population in lakes under heavy human influence (38268)

The objectives of this project are to improve our understanding of how the physical conditions of lakes can affect spawning and fry mortality and growth for the most important piscivorous fish species. We will especially focus on the conditions of the littoral zone. This knowledge can be used to insure that the demands of these species in relation to spawning and YOY development are met. The results will be used as part of the web-based “Handbook on the Management of Lake Fish”, which is under development.

The majority of Danish lakes are strongly influenced by human activity, partly in the form of increased nutrient load, but also direct physical alterations are common, e.g. by regulation of the water level, consolidation of the banks or the consequences of heavy boat traffic. These types of physical alterations are often most common in lakes situated in or close to urban areas. In these kinds of lakes, lake restoration by biomanipulation might prove to be insufficient to achieve the improved environmental conditions expected, including a good population of piscivorous fish. Thus, the lakes environmental quality, as well as the possibility to use the lake for recreational activities including recreational fisheries, might be negatively influenced.

During the project, several activities related to this subject have been conducted:
1. An experiment demonstrating the importance of water depth for the mortality of 0+ pike.
2. Another experiment, which showed that it is possible to build an artificial spawning habitat for pike in an urban, artificial lake without a natural littoral zone and that the pike did use it for spawning and that the pike fry used it as nursery habitat.
3. A stocking experiment with 0+ pike to find out if stocking is a possible way to enhance a very low population density of pike in a lake with heavy boat traffic and extensive angling. During this experiment we demonstrated that it is possible to tag 0+ pike of 6-8 cm with PIT tags without mortality, but also that the tagging has a negative effect on growth of the tagged pike.
4. An investigation on the spawning habitat choice and spawning behavior of pike in a small natural lake (in cooperation with project no 39270).

The use of specially designed “egg traps” has been used successful in two of these experiments.

The project is coordinated by DTU Aqua.

Research area: Freshwater Fisheries and Ecology