The porpoise population in inner Danish waters has plummeted by more than half in the last ten years, prompting concerns from researchers and environmental organizations. A recent memo from DCE – National Center for Environment and Energy at Aarhus University reveals the alarming decline of the only whale species that breeds in Danish waters.

In 2022, the Belt Sea population, inhabiting the Kattegat, the Belts, and the western Baltic Sea, was estimated at 14,200 individuals. This figure represents a drastic reduction compared to the approximately 40,000 porpoises estimated in 2012. The intergovernmental organization Helcom (Helsinki Commission) is poised to upgrade the porpoise’s red list assessment from “vulnerable” to “endangered” in its next update due to the severity of the situation.

The decline is attributed to a combination of factors, including food scarcity, a deteriorated marine environment marked by increased oxygen depletion, and the mortality of porpoises in fishing nets.

Researchers suggest that the trend can be reversed by improving conditions for porpoises in specific areas near Lillebælt and Flensborg Fjord, where food resources remain available. Restoring stone reefs to create new habitats for prey species like herring and cod is one proposed solution.

Furthermore, the memo suggests implementing speed limits and reducing noise pollution from ship traffic. Noise and disturbances from shipping negatively impact the porpoise population, making them extra vulnerable in narrow parts of the belt where they have limited ability to avoid noise and traffic. Researchers recommend that all vessels in Naturpark Lillebælt reduce their speed to a maximum of five knots.