Hungry humpbacks outcomes so far

With SGHT and FOSGI support, the Hungry Humpbacks project team conducted four successful field seasons collecting data on humpback whale body size and condition, both on migration south to South Georgia (Dr Eduardo Camargo, Abrolhos Bank, Brazil) in 2023, in South Georgia in 2024 and 2025, and on migration north towards breeding grounds (Dr Rodrigo Tardin in Cabo Frio, Brazil) in 2024. To best understand how rapidly whales gain weight, they needed to be separated by sex, pregnancy status, and age (juvenile/adult), since each of these categories has different foraging needs. South Georgia data was processed by colleagues at BAS and St Andrews, while Brazil data was processed by colleagues at University of São Paulo and Pontifícia Universidade Católica do Rio Grande do Sul. Dr Fredrik Christiansen at Aarhus University, Denmark is a world expert on using these data to measure whale weight gain.

Fieldwork in Abrolhos Bank, Brazil

Fieldwork in Cabo Frio, Brazil

Drone images from South Georgia, showing (left to right) humpback whale, southern right whale female with calf and Antarctic blue whale female and calf

So far Fredrik’s used the images to estimate the total energy intake for a 11.2m (standard size adult) humpback whale, 3,700MJ/day. Considering the caloric value of krill, he estimates that such an adult whale needs to eat  ~800 kg of krill a day (range=675-960kg) to experience the mass gain which has been observed during the South Georgia feeding season. Feeding requirements vary with whale body length, so mean prey consumption varies from 650 to 1200 kg/day (9.3 to 2.2% of body mass) for whales with body lengths of 8 to 16m. Fredrik is now finalising this analysis with all the additional data on the sex and pregnancy status of the whales surveyed, so that he can accurately measure prey consumption across the humpback population. This study will conclude next year so watch this space for an update!

Example aerial images of (A) a humpback whale and (B) a southern right whale, showing how the measurements are done.

Susannah Calderan’s work on Antarctic blue whales

Susannah Calderan from the Scottish Association for Marine Science collated thirty years of sightings, acoustic surveys and photo-identifications of blue whales in the waters around South Georgia, to review their current distribution and any trends in sightings from 1998 to 2020. She found that while blue whales were scarcely seen before 2018, there has been an increase in sightings and acoustic detections since then, particularly during a 2020 survey of the island, when 58 blue whale sightings were reported in 26 days of survey, and their vocalisations were recorded all around the island. Considered all together, the data suggest critically endangered Antarctic blue whales are returning to South Georgia waters after decades of absence, perhaps as their populations recover from whaling. This exciting work was reported by the BBC and made headlines around the world. You can read more about the work here.

Antarctic blue whale at South Georgia. Image: Amy Kennedy