Oxygen depletion in Baltic Sea reaches alarming levels during Dana expedition

The research vessel Dana from DTU Aqua is currently gathering concerning data during its autumn expedition in the Baltic Sea. Six months ago, scientists reported a boost of fresh oxygen reaching the Baltic from the North Sea, but current findings tell a different story.

Marie Storr-Paulsen, a biologist and expedition leader on Dana, shared that the oxygen depletion observed this year marks the worst decline in the past three years. This alarming news follows a report by the National Center for Environment and Energy earlier in the year, which indicated the largest oxygen depletion in Danish waters in 22 years.

DTU Aqua conducts biannual assessments of oxygen levels and fish populations in the Baltic Sea, maintaining a consistent methodology to ensure that their data can be correlated with that from other neighboring countries.

The study indicates a significant impact of low oxygen levels on cod populations, as their primary food sources, bottom-dwelling organisms, are mostly absent. Storr-Paulsen noted that cod captured in areas experiencing severe oxygen depletion had completely empty stomachs.

Recent measurements reveal that cod around Bornholm have shrunk to roughly half their typical size, with the largest specimen caught during this expedition measuring 49 centimeters. However, the majority of cod retrieved are only around 22-24 centimeters.

There is a silver lining, as Storr-Paulsen pointed out that Baltic cod spawn late in the season. The presence of juvenile cod measuring about seven centimeters caught during this expedition indicates that spawning is still occurring, although the young fish are not growing as large as they should. The current expedition on the Dana is scheduled to conclude on November 22nd.