Salmonid freshwater habitats (38256)

The procurement of knowledge in this project aims at improving the basic available knowledge for advising on restoration and stream maintenance activities. Realizing that the question of stream restoration is huge, focus is on selected issues often in cooperation with external partners whenever relevant. Regular cooperation has been done with other Danish universities (Roskilde University, Aalborg University, Aarhus University), local authorities, Environmental centers and anglers associations.

In the coming years it is expected that several issues will be particularly relevant, such as stream restoration (removal/sanitation of barriers and restoration of spawning areas), implementation of EU Water plans, fine sediments and sand transport in streams. Realizing that erosion and transport of fine sediment (sand) is a major problem in many Danish streams, several methods to mitigate this have been tested. One attempt to prevent the embedment of excessive amounts of fine sediment in spawning gravel, has been placing tubes below the gravel in order to allow the sediment transported by the stream to be transported past the area with spawning gravel. Investigations on artificial spawning areas constructed with tubes will be carried out by measuring the content of fine sediment in the gravel on comparable artificial gravel areas with and without tubes.

A database with ongoing and previous stream restoration projects has been created. This is continuously being updated, to enable meta-analysis on relevant variables with the purpose of providing advice on restoration projects. Focus will be on the identification of factors influencing restoration effects towards fish populations.

A number of restoration projects (addition of spawning gravel) are being followed over a longer time span (years). Habitat parameters such as depth, water velocity, substrate composition and vegetation cover was initially measured before the restoration together with fish species and size composition. The same variables are measured annually to register effect from and durability of the restoration.

In a stream where approximately half of the productive area was previously inaccessible to migrating trout, all obstacles are being removed in a major restoration project. Habitat parameters are measured for the entire system, aiming at modelling the effect of the removal of barriers on trout production (cooperation with project 38259).

In a study on brown trout population dynamics and effects on the population from sports fishing, two sections (total length approx. 8 km) have been mapped for habitat quality. All fish with sufficient size for tagging inside the two sections have been tagged (PIT tags) and migrations in and out of the experimental section is monitored. A controlled fishing pressure is being applied to one of the sections in order to evaluate the effect on trout population from sport fishing.

The project is coordinated by DTU Aqua.

Research area: Freshwater Fisheries and Ecology