Cruise report from R/V Svea week 34-35, 2025

SMHI performed an oxygen and nutrient mapping survey within SLU Aqua’s cruise; International Bottom Trawl Survey (IBTS Q3), that covers the Skagerrak, the North Sea and the Kattegat. SMHI joins the cruise to perform CTD measurements in connection to each trawl and to take water samples for nutrients, chlorophyll, pH-tot and oxygen. One of SMHIs standard stations; Anholt E were also visited during the cruise. SMHI also assisted SLU-Aqua to take water samples close to the bottom for analysis of fish eDNA.

In the south-eastern parts of Kattegat, in the Skälderviken, oxygen levels were below the limit for acute hypoxia, < 2 ml/l. In acute oxygen deficiency, most benthic animals are negatively affected. Most parts of Kattegat's bottom water suffered from hypoxia. The oxygen levels in the bottom water ranged from just below 3 to 4 ml/l. Below 4 ml/l, the first signs of oxygen deficiency in marine organisms are normally detected. In Skagerrak the oxygen levels in open water was generally good while hypoxic conditions were found at one costal station in Skagerrak.