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International research project aims to develop effective protection for harbour porpoises in the Baltic Sea
Photo: Lana Tannir, Fjord&Bælt
14 partners from Germany, Denmark, Sweden, Estonia, Finland and Lithuania have joined forces to develop effective conservation measures for the critically endangered harbour porpoise in the Baltic Sea. The five-year project, led by Ocean Museum Germany, aims to evaluate scientific data on the population’s structure and threats, as well as the quality of the porpoises’ habitat in the Baltic Sea. NIRAS is one of the Danish partners, which also include Aarhus University and Museum Vest.
July 2, 2026
The harbour porpoise, the only native, breeding species of whale in the Baltic Sea, is divided into two distinct populations. The population in the central part of the Baltic Sea now numbers only a few hundred individuals and is critically endangered. The larger population in the Danish Belt Sea is also in decline and has been classified as endangered by the International Union for Conservation of Nature (IUCN).
Significantly reduced populations
“Over the past one hundred years, the Baltic Sea population has been decimated to around 500 individuals due to a combination of by-catch and environmental pollutants, whilst the Danish Belt Sea population has been reduced to around a third over the last 20 years. The most likely cause is by-catch combined with a reduction in the food supply due to overfishing and oxygen depletion. When the fjords die, the porpoises will also lose their means of survival,” says Line A. Kyhn, project manager at NIRAS.
“So far, however, only very limited conservation measures have been implemented, and that is why this project has been launched, as the German authorities wish to lay the foundations for effective species conservation.”
“So far, however, only very limited conservation measures have been implemented, and that is why this project has been launched, as the German authorities wish to lay the foundations for effective species conservation.”
Line A. Kyhn, project manager, NIRAS
Urgent measures
The research project entitled “CUMBIAH” (“Conservation Union for Management of the Baltic Harbour Porpoise Populations and their Habitat”) aims to address a wide range of research questions in order to develop urgently needed and effective conservation measures to be implemented in the partner countries.
In particular, the evaluation of the latest studies and the assessment of the porpoises’ distribution patterns and density will improve our understanding of current population sizes and trends. Acoustic data collected in 2024–25 by all participating countries will be used to estimate the total population in the Baltic Sea. This data collection was funded by the Aage V. Jensen Charity Foundation and the Danish Ministry of Environment.
"For the porpoises in the inner part of the Baltic Sea and in the Danish Belt Sea, it may be crucial that new knowledge is translated into targeted protection of both the animals and the habitats on which they depend."
Line A. Kyhn, project manager, NIRAS
From click sounds to quantification
“As part of my PhD thesis, I developed one of the very first models for converting recorded click sounds from porpoises into porpoise numbers, and I helped to design the basis for this conversion. So it will be incredibly exciting to be part of this work and finally see how the Baltic Sea population is actually faring since it was counted in 2011–13,” says Line A. Kyhn.
“Regular monitoring of a population is the only way we can really know how it is faring. It is essential if we are to be able to intervene in time, before a population disappears – which is the course the Baltic Sea porpoise is currently on unless there is very rapid and effective intervention. For the porpoises in the inner part of the Baltic Sea and in the Danish Belt Sea, it may be crucial that new knowledge is translated into targeted protection of both the animals and the habitats on which they depend.”
One research project, many outputs
Furthermore, the project will seek to develop a method for the acoustic identification of porpoise calves to help determine calving times and nursing areas. Environmental DNA (eDNA) samples will be analysed to assess habitat quality and the presence of prey fish species. Monitoring of stranded animals and post-mortem examinations will provide important insights into the general physical condition of porpoises in the Baltic Sea and the Belts, including nutritional status, sex, reproductive status, disease and cause of death.
Furthermore, genetic data will be used to link individuals to their original population, assess genetic diversity and estimate population sizes and trends. Information on fishing intensity will provide insight into the risk of bycatch. Measurements of underwater noise from construction projects and seismic surveys will be compared with porpoise density and distribution patterns to identify areas in particular need of protection.
NIRAS’s role in the project includes carrying out noise measurements on trawlers and conducting geophysical surveys to provide input for the assessment of habitat quality, as well as contributing to the analysis of acoustic data on porpoise density. In addition, NIRAS also collects stranded porpoises.
The project will run for five years and is funded by the German Federal Ministry for the Environment, Climate Action, Nature Conservation and Nuclear Safety (BMUKN) with funds earmarked for marine nature conservation under the Offshore Wind Energy Act.
Read more about the research project at Ocean Museum Germany.
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