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New study: the grey seal is not the reason that Baltic cod stock is in crisis

This weekend, an article was published in the scientific journal AMBIO: A Journal of the Human Environment. The article states that the grey seal is not the reason for the Baltic cod´s crisis.

Monika Winder is a professor at the Department of Ecology, Environment and Plant Sciences at Stockholm University. She is also one of the co-authors of the study. In the Swedish Newspaper Dagens Nyheter Monika says:
"Our research shows that seals do eat a lot of fish, but if we compare their impact with the impact of professional fishing or climate impact, it's not nearly as big."

The study is based on the area known as the Baltic Proper and focuses on fish stocks in open waters. The study is conducted by researchers from the University of British Columbia, Stockholm University and the Swedish University of Agricultural Sciences (SLU).

"We have about 30,000 grey seals in the area today. Our research shows that we could have 100,000 seals in the same area without affecting stocks of cod, herring and sprat to the same extent as the fishing industry, climate change and eutrophication", says Monika Winder in Dagens Nyheter.

Since the study focuses on fish stocks in the open sea, it cannot be deduced from the conclusions of how the seal population affects fish species such as salmon, eel or perch living near the coast. This is where most interactions between fishermen and seals occur.

Cod, herring and sprat are part of a sensitive ecosystem. The cod´s condition is a clear indication of the general health of the Baltic Sea, says Inger Näslund, Senior Advisor Marine and Fisheries at the World Wide Fund for Nature (WWF). When cod stocks decrease, chances are that the cod's main food, herring and sprat, increase. An increased stock of herring and sprat leads to increased predation on zooplankton, which generates less competition for phytoplankton in the Baltic Sea. It contributes to eutrophication and anoxic bottoms, which makes it even more difficult for cod to survive.

The above text is a summary of an article in Dagens Nyheter. Read the entire article "Studie: Gråsälen inte största hotet mot Östersjötorsk" here (only in Swedish).

The study was published on December 8, 2018 in the scientific journal AMBIO: A Journal of the Human Environment. You can read the entire article about the study here: “The necessity of a holistic approach when managing marine mammal - fisheries interactions: Environment and fisheries impacts are stronger than seal predation”.