Abundance and distribution of fin and humpback whales at the South Orkney Islands in the austral summers 2011-2025

Information on cetacean population status is vital for determining fisheries management strategies, especially where they overlap spatiotemporally and target the same organism. This study aims to quantify distribution and abundance of fin (Balaenoptera physalus) and humpback whales (Megaptera novaeangeliae) near the South Orkney Islands, an area in the Southern Ocean with the highest catches of Antarctic krill (Euphausia superba). Ship-based observational data were collected during the austral summers from 2011 to 2025. Most fin whale sightings were over the northern shelf-break and deeper offshore regions, with an annual density between 0.01 and 0.29 individuals per km^-2 (corresponding to a summer abundance range of 648-18 083 individuals). Humpback whales were mainly sighted north of the islands but more on-shelf, with annual densities between 0 and 0.07 individuals per km^-2 (average 590 individuals, with a summer abundance range of 0-4486 individuals). Summer abundances varied substantially, with fin whales increasing significantly (0.02 individuals per km^-2 per year, P-value 0.03), while no monotonic increase was detected for humpback whales. This study demonstrates that the South Orkney Islands constitute a key area for fin whales during the summer season, where they play a significant role as major consumers of krill. There is further need for knowledge about cetacean krill consumption, as well as to map their annual presence in this area and to describe how krill density, biomass, and distribution vary throughout the season. This understanding is crucial to determine how whales contribute to nutrient cycling through their feeding activities, and for contributing to fisheries management regulations.