The porpoise population in inner Danish waters has more than halved in the last ten years, raising concerns about the future of the only whale species that breeds in the area.

A recent report from DCE – National Center for Environment and Energy at Aarhus University indicates a significant decline in the Belt Sea porpoise population, which inhabits the Kattegat, the Belts, and the western Baltic Sea. In 2022, the population was estimated at 14,200 individuals, a sharp contrast to the approximately 40,000 porpoises recorded in 2012.

The intergovernmental organization Helcom (Helsinki Commission), dedicated to protecting the Baltic Sea’s marine environment, is poised to upgrade its red list assessment for porpoises from “vulnerable” to “endangered”.

The decline is attributed to several factors, including food scarcity, a deteriorating marine environment characterized by increased oxygen depletion, and the entanglement of porpoises in fishing nets.

However, researchers believe that the trend can be reversed by improving conditions for porpoises in specific areas, such as Lillebælt and Flensburg Fjord, where food sources are still available.

Possible improvements involve restoring stone reefs to create new habitats for prey like herring and cod.

Introducing regulations on speed limits and noise reduction for ship traffic could also have a positive impact. Noise and disturbances from shipping negatively affect the porpoise population. The report recommends that all vessels in Naturpark Lillebælt reduce speed to a maximum of five knots, especially in narrow parts of the belt where porpoises are particularly vulnerable to disturbances due to limited opportunities to avoid noise and traffic.