Findings for the Western Baltic Sea: Climate change and agriculture are also killing cod

Results for the Western Baltic
Climate change and agriculture are also killing cod

06/19/2022, 5:55 PM

It was once the main source of income for fishermen – but then the cod stock in the western Baltic collapsed. Researchers are eagerly looking for causes. And now we have the lead.

The cod stock in the western Baltic is not only threatened by overfishing. Climate change and excessive fertilization from agriculture also play an important role. Scientists from the Thünen Institute for Baltic Fisheries confirmed this with new studies, such as NDR communication. The NDR accompanied the research to the study for several months.

“We were very surprised by the diffusion of low-oxygen water during the summer months from the bottom of the Baltic Sea to the upper layers,” says Uwe Krumme of the Thünen Institute. “There it hits directly over the superheated layers of water. And where that happens, there is no longer any habitat for the cod” – that is, there is no longer a place where these fish can survive. The new data is “extremely alarming”. The Thünen Institute plans to publish the final results of the study next year.

For decades, cod has been a major source of income for fisheries in the western Baltic Sea. But the stock collapsed two years ago. Due to climate change, the surface of the Baltic Sea is getting warmer and warmer. Low oxygen dead zones are scattered on the sea floor. According to the study, this is caused by over-fertilization in coastal agriculture, where manure reaches the Baltic Sea via streams and rivers. There is an overgrowth of algae. The algae, in turn, sink to the bottom and are decomposed by bacteria that consume the oxygen in the water.

For ten months, the institute recorded environmental data such as oxygen and salt content as well as water temperature in a five square kilometer research field in Mecklenburg Bay. To do this, the researchers installed a total of 30 measuring stations on the sea floor. The project is a collaboration with the Leibniz Baltic Research Institute. The Western Baltic almost covers the part of the sea west of the line from Dares to Falster.