Experts make alarming discovery after analyzing species for over 2 decades: 'Evolution in action'

Overfishing in the Bornholm Basin over the last several decades has made eastern Baltic cod shrink in size.

What's happening?

As Mongabay observed, a June 2025 study by GEOMAR stated that eastern Baltic cod have shrunk over time. 

Between 1996 and 2019, they lost about half their length and almost four-fifths of their typical weight.

While fishing wasn't a variable tracked by the study, the researchers still believe it caused this rapid evolution to an extent. 

Trawling companies were only allowed to catch fish over 14 inches long to protect juvenile fish. But as of 2019, trawling has been banned.

The study, published in the journal Science Advances, looked at the DNA of the fish to confirm this change. Researchers found that the gene patterns of smaller fish have become more common over time. 

"What we are observing is evolution in action, driven by human activity," said Professor Dr. Thorsten Reusch, one of the study's co-authors, in a press release. "This is scientifically fascinating, but ecologically deeply concerning."

Why is overfishing concerning?

Overfishing can severely damage our food supply chains and our ecosystems.

According to the World Wildlife Fund, the global fishing industry is worth about $362 billion. If we continue to overfish, people will lose their jobs and sources of income. Overfishing exploits coastal economies and causes financial instability.

It also threatens the survival of many marine animals. When overfishing takes fish out of the equation, that creates an imbalance within marine ecosystems. It could also lead to severely endangered species like the vaquita porpoise and Maui's dolphin going fully extinct.

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What's being done about overfishing?

The banning of trawling in 2019 demonstrates the importance and value of taking action and spreading the word about environmentally harmful practices. 

It may take a long time to reverse the damage done to eastern Baltic cod, but researchers hope the tides will change for these fish.

"That's why a paper like this is so important," David Conover, a professor emeritus in biology at the University of Oregon and a co-author of a related 2019 study, told Mongabay. "It's going to up the dialogue and increase conversations in the management community."

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