Cormorants consume large share of threatened cod

A new study by DTU Aqua shows that cormorants are eating a significant portion of small cod and flounder in Danish waters, with around 70 percent of tagged fish ending up in the birds’ stomachs.

The research, conducted in Genner Bay in the southern Little Belt in 2022 and 2024, involved marking approximately 5,000 small cod and flounder with electronic chips. Scientists later recovered the chips from cormorant colonies, where the birds had regurgitated them after digestion, according to senior researcher emeritus Niels Thorvald Jepsen, who led the study.

Jepsen called the findings surprising, noting the high predation rate over a relatively short period of two to seven months. He hopes the study will provide new insights into the factors depleting fish stocks, particularly cod, in coastal areas and the Baltic Sea.

Cod stocks in Danish waters are already under pressure. Last year, the International Council for the Exploration of the Sea recommended a complete ban on cod fishing in Danish waters for the first time.

Kaare Ebert, a biologist with the Danish Anglers Association, argued that stricter cormorant regulation is necessary to protect fish populations, though he acknowledged that coordination with Germany and Poland may be needed, as cod migrate across the Baltic.

However, Thomas Bregnballe, a senior researcher at Aarhus University’s Department of Ecoscience, cautioned that cormorants are not the sole cause of declining cod stocks. Rising sea temperatures, bottom trawling, and oxygen depletion due to eutrophication also contribute to the fish’s difficult conditions.