Migratory fish in German waters

Background and Objective

Diadromous fish species suffer in particular from the massive modifications of rivers and estuaries (e.g. through hydropower plants and fairway modifications). The strong modification of water bodies significantly restricts the migration movements of fish and has a major influence on the flow dynamics of rivers from the upper reaches to the tidal area. Together with fundamental water quality problems in many areas (high sediment and nutrient input, pollution, rising temperatures), this has already led to a significant loss of spawning and nursery habitats for many fish species and reduced their numbers. In Germany, there is a lack of basic information on the population situation and population structure of many migratory fish species, as well as on their current distribution and important migration routes. Against this background, the project aims to significantly improve the data basis for migratory fish species in Germany and is working towards the development of a permanent monitoring system for effective population management and adapted species protection for these species, which have so far received little attention.

Target Group

EU. ICES, Bundesländer (the German federal states)

Approach

In a first step, a comprehensive literature and data research is carried out as a basis for the final design of the study. In Germany, there are numerous efforts at regional and local level to support endangered migratory fish species and populations, e.g. through reintroduction measures, or to survey and document the occurrence of certain species in individual water bodies. Since the implementation of the Water Framework Directive, data on the occurrence of fish in inland waters has also been collected regularly in the federal states. It is planned to compile an overview of individual migratory fish species and identify data gaps by comprehensively recording and analyzing this data collected at the federal state level and by evaluating historical data records in available databases. In addition, scientific studies and existing reports are to be reviewed and evaluated.

In addition, further investigations are planned to close identified data gaps. Therefore, the existing fish monitoring activities for individual species in selected water bodies will be expanded and supplemented by accompanying studies. The potential study area extends mainly to inland waters, but does not exclude marine waters of the North Sea and Baltic Sea. In particular, non-invasive detection methods, such as the analysis of environmental DNA (eDNA), will be used. In addition to the area-specific detection of species, it is planned to develop species-specific methods for the quantitative assessment of selected fish species using eDNA analyses and to compare them with catch-based methods. In addition, the use of different fish markers (e.g. PIT tags, acoustic transmitters, data storage tags, satellite tags) will be used to determine the migratory behavior and habitat preferences of migratory fish, supplemented by biological investigations (such as age determination and pollutant and parasite contamination). In addition, the use of citizen science methods such as surveys of recreational fishers and other stakeholders will be examined.

Our Research Questions

• Comprehensive analysis and evaluation of existing data on migratory fish in German waters. Identification of data gaps and strategies for collecting missing data in the future.
• Development of concepts for the expansion of monitoring activities in selected water bodies to improve the data basis for individual migratory fish species. Development of species-specific methods for the detection of migratory fish in different types of water bodies on the basis of eDNA analyses.
• Development of proposals for improved species-specific stock management.