Young pike. Photo: Finn Sivebæk

Freshwater fisheries and ecology

DTU Aqua’s research in the field of freshwater fisheries and ecology is focused on the behaviour of particular species of fish and their interaction with the environment

Main themes

DTU Aqua’s research on freshwater fisheries and ecology is centered on understanding the individual behaviour of fish as a step towards understanding overall environmental mechanisms. The research includes studies of fish habitats in streams, lakes and coastal areas and how natural factors and human activity affect the conditions under which fish live. 

We investigate the effect of deterioration of aquatic habitats and the difficulties faced by fish when they migrate, including the effect of physical barriers in streams, nutrient-rich lakes and the construction of new lakes and wetlands in streams.

Freshwater fisheries and ecology research has three main themes:

  • Migratory behaviour 
    Many species of fish migrate. We examine the extent to which genetic and environmental factors affect whether fish migrate, where they migrate to, and how far they migrate. One method used to investigate this is the development and application of various techniques for tagging fish, e.g. telemetry. 

  • Relationship between predator and prey
    Fish are both predators and prey. Knowledge about different fish and their role in the food chain allows us to re-establish sustainable fish habitats. For example, we look at the distribution and concentration of fish in relation to the seasons, the time of day and the chemical and physical conditions in the water. We also study the bottlenecks for fish populations of which predation, mainly from birds, have been documented to be very important. 

  • Restoring natural fish populations
    We monitor selected populations of freshwater fish. The results of this research are used to improve fish habitats and to assess and support fish populations that may have problems surviving on their own.

Why research on freshwater fisheries and ecology?

Up until the 1970s, many streams were channelized, regulated and deepened. This was mainly done to increase the capacity of the streams to drain water turning adjacent bogs and ponds into farmland.

Over the years, water quality has deteriorated as a result of human activity, including the discharge of sewage and the overuse of fertilizers in surrounding farmland.This anthropogenic impact has resulted in degraded fish habitats and reduced quality of plant and animal life in and around streams and lakes.

In recent years, awareness of environmental issues and sustainable use of resources has increased. At the same time, there is an increasing need to address the human dimension in management of recreational fisheries. This has led to an increased need for knowledge about the aquatic environment and fish stocks. 

To safeguard biodiversity and to ensure the best possible conditions for recreational fishing, DTU Aqua works extensively with the sustainable management of freshwater areas in combination with carefully maintaining fish stocks at a harvestable level. 

What is the research used for?

The results of our research are used predominantly for advisory purposes. DTU Aqua currently provides consultancy services for the Ministry of Environment and Food of Denmark as well as for a number of municipalities and several NGO’s.

We give advice particularly on how wild fish stocks can be supported, preserved and used in a sustainable way, taking into account important aspects of interest to the public.