Increasing seal population will not harm largest fish stocks in the Baltic

Date:  December 10, 2018

Source:  Stockholm University

Seals feeding on fish does not decrease fish stocks of Baltic cod, herring and sprat the most -- climate change, nutrient load and fisheries do, shows a new study from Stockholm University.

It has long been debated whether the seal predation of fish play a major role in the fish decline in the Baltic Sea compared to human fishing. The debate escalated worldwide since conservation efforts to protect seals and fish-eating birds resulted in increased number of them.

A new study taking into account human pressures on the environment, shows that the seals are not the main problem on commercial fish stocks in the open water of the Baltic Sea.

"We currently have 30,000 grey seals in the Baltic Proper, but we can even have more than 100,000 seals and it will still not affect the amount of cod negatively as much as climate change, nutrient load and fisheries. The Baltic is very sensitive to human impact," says David Costalago, a former postdoctoral researcher at Department of Ecology, Environment and Plant Sciences, Stockholm University.

The cod population size for example, decreased more by environmental change and by human fishing, than the seals eating the fish. How much fish the seals eat is also affected by the climate and nutrient load.

Continued