Density and abundance estimates of baleen whales recorded during the 2019 DY098 cruise in the Scotia Sea around South Georgia and the South Sandwich Islands

We use cetacean sightings data collected from the northern and eastern Scotia Arc (CCAMLR Subareas 48.3 and 48.4) during the 2018/19 international synoptic krill survey to provide preliminary density and relative abundance estimates for humpback whales (Megaptera novaeangliae), fin whales (Balaenoptera physalus) and for all other baleen whale species sighted. The survey was designed to collect data on the abundance of krill and so was not optimised for deriving design-based cetacean abundance estimates, but may provide a useful means of comparing whale densities and habitat use patterns between the present day and the CCAMLR-2000 synoptic survey. Humpback whales were the most frequently sighted cetacean species during the survey (226 sightings of a total count of 495 whales) and were widely distributed east of 42.5°W in all water depths surveyed, with fin whales the next most commonly sighted species (53 sightings and a cumulative count of 76 whales). Humpback whale abundance in South Georgia (Subarea 48.3) was estimated at 20,333 (95% CI 13,988-29,555) with all baleen whales estimated at 27,143 (95% CI 19,998-36,842). Humpback whale abundance around the South Sandwich Islands (Subarea 48.4) was estimated at 10,893 (95% CI 7,818-15,178) with all baleen whales estimated at 20,699 (95% CI 16,027-26,732). Fin whale abundance over all strata was estimated at 6,002 (95% CI 4,056-8,881). The estimates for humpback whales are consistent with the high recent estimates of abundance and trend from their Brazilian wintering grounds. These new estimates of abundance can also be used to re-assess the annual impact of krill-feeding whales within the Scotia Arc ecosystem, sensu Reilly et al. (2004).