Baltic cod are fatter than expected as oxygen surprises researchers

Cod caught during a survey of the Baltic Sea were in better condition than researchers expected, while oxygen levels near Bornholm were higher than forecast, DR reports.

Researchers from DTU Aqua found the fish during the first part of the research vessel Dana’s autumn survey. The cod were not truly fat, but were thicker than those caught in recent years, when they were very thin, said Marie Storr-Paulsen, a section head at DTU Aqua.

Researchers had expected oxygen depletion to be as severe as in recent years, or worse, after a warm summer with large blooms of blue-green algae around Bornholm. Instead, they found oxygen at many of the deep-water monitoring stations.

Storr-Paulsen believes fresh oxygen-rich water entered the area from the western Baltic Sea in spring. Bottom-dwelling animals used the oxygen to grow, providing food for cod over the summer, while some of the oxygen-poor water was pushed away.

The situation could change quickly, she cautioned. Large parts of the eastern Baltic Sea remain vulnerable to oxygen depletion.

The Dana is halfway through its autumn survey and will continue east after a stop in Rønne harbour. The findings will contribute to an overall assessment of the Baltic Sea, alongside measurements from other Baltic countries.