Antarctic krill and ecosystem monitoring survey off the South Orkney Islands in 2025

Environmental monitoring at the South Orkney Islands in the Southern Ocean has been conducted annually since 2011 by the Institute of Marine Research, Norway. Hydro-acoustic and net-derived data are utilized to calculate the biomass of Antarctic krill (Euphausia superba) and to assess the spatial distribution and demographic composition of krill, other zooplankton, and fish taxa. Systematic sighting data of cetaceans, penguins, and pinnipeds are recorded along the transects during daylight hours. Additionally, data acquisition from sensors anchored to the seabed since the previous year is part of the procedure. This report presents the survey activities from 2025 and provides preliminary results.
The main result from this year's survey was the estimated krill biomass of 6.16 million tons (CV: 0.74). A total of 38 taxonomic groups were identified from the trawl catches, with 18 determined to species level. The largest catch weights were recorded in the northernmost and deepest parts of the study area, with Salpa thompsoni dominating, while larger catches of E. superba were found on the shelf slope. Three species of euphausiids were identified: E. superba, E. triacantha, and Thysanoessa macrura. The siphonophore Diphyes antarctica was the most frequently occurring species, found at 24 of a total of 28 stations, followed by E. superba and T. macrura at 23 and 21 stations, respectively. The mean body length of E. superba was 42.6 mm (SD: 6.6), ranging from 25.3 to 59.4 mm. The demographic composition was dominated by adult males (stage M3B, 20.4%), females (stage F3D, 22.3%), and juveniles (15%). The 2025 survey also estimated fin whale (Balaenoptera physalus) density to 0.18 ind. m-2 (0.14-0.25 95% CI) and humpback whale (Megaptera novaeangliae)  density to 0.07 ind. m-2 (0.04-0.12 95% CI).