Climate change and agriculture are also killing cod

Results for the western Baltic Sea

Climate change and agriculture are also killing cod

06/19/2022, 5:55 p.m

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

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

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

Cod has been an important source of income for fisheries in the western Baltic Sea for decades. But the stock collapsed two years ago. Due to climate change, the surface of the Baltic Sea is becoming warmer and warmer. Oxygen-poor dead zones are scattered on the sea floor. According to the study, the reason for this is over-fertilization in coastal agriculture, where liquid manure enters the Baltic Sea via streams and rivers. There is excessive algae growth. The algae, in turn, sink to the bottom and are decomposed by bacteria, which use up the oxygen in the water.

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