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Population abundance of recovering humpback whales (Megaptera novaeangliae) and other baleen whales in the Scotia Arc, South Atlantic

Mick Baines*, Natalie Kelly, Maren Reichelt, Claire Lacey, Simon Pinder, Sophie Fielding, Eugene Murphy, Phil Trathan, Martin Biuw, Ulf Lindstrøm, Bjørn A. Krafft, Jennifer A. Jackson

*Corresponding author:

ABSTRACT: Following the cessation of whaling, South Atlantic populations of humpback (Megaptera novaeangliae) and some other baleen whale species are recovering, but there has been limited monitoring of their recovery in the Scotia Arc, a former whaling epicentre and a hotspot for Antarctic krill (Euphausia superba). To inform the management of krill fisheries, up to date assessment of whale biomass and prey consumption is essential. Using a model-based approach, we provide the first estimates of whale abundance and krill consumption for South Georgia and the South Sandwich Islands, and total abundance of humpback whales across their southwest Atlantic feeding grounds, using data collected in 2019. Humpback whale abundance was estimated at 24,543 (CV = 0.26; 95% CI 14,863 – 40,528), similar to that measured in Brazil on the main wintering ground for this population. The abundance of baleen whales in South Georgia and the South Sandwich Islands, including those not identified to species level, was estimated at 43,824 (CV = 0.15; 95% CI 33,509 – 59,077). Based on the proportion of humpback whales identified during the surveys (83%), the majority of these are likely to be humpback whales. Annual krill consumption by baleen whales was estimated to be in the range 4.8 – 7.2 million tons, representing 7 - 10% of the estimated krill biomass in the region. However, there is a need to better understand feeding rates in baleen whales, and further research into this field should be a priority in order to improve the accuracy and precision of prey consumption rate estimation.