Hungry Humpbacks

Whales are the largest krill predators in the UK Overseas territory of South Georgia, yet their impacts on krill stocks are poorly understood. Recently, whale surveys revealed high summer abundance and extended use of South Georgia waters into winter, coincident with the winter krill fishery. This DARWIN PLUS project measures how humpback whale foraging intensity varies across the feeding season in South Georgia, using UAV-based (drone) measurements of body condition and satellite-tracking of whale diving rates to measure season-specific krill consumption, and inform krill quota-setting for the Subarea 48.3 CCAMLR krill risk assessment.

The UAV pilots will collect calibrated UAV aerial images from humpback whales near Cumberland Bay, South Georgia. Small-boat surveys will also be conducted near Cumberland Bay, collecting whale sightings, photo-identifications and biopsy samples. Humpback whales will be instrumented with depth-recording satellite tags, to identify spatial habitat-use and how foraging depth and intensity varies across the feeding season.

This project will provide seasonal krill consumption estimates for humpbacks and generate satellite tracking-based winter habitat use models to describe whale distribution. Both datasets will be integrated into the CCAMLR Area 48.3 krill risk assessment and will provide baseline measurements of krill consumption in South Georgia waters by whales across seasons.

Funding: Darwin Plus, South Georgia Heritage Trust and Friends of South Georgia Island. Logistical support from the Government of South Georgia and the South Sandwich Islands.

Follow the progress of the project here: https://twitter.com/wildwaterwhales

HIGHLIGHTS SO FAR

The first Stakeholders meeting for the Hungry Humpbacks project was held on the 5th September 2023. You can find excerpts of this meeting here.

The first field leg of the project took place in Abrolhos Marine National Park, Brazil from 20 September to 17 October 2023, recording the body condition of humpback whales at the end of their breeding season before they migrate south towards their feeding grounds in South Georgia and the Scotia Arc.

During this field project, a total of 121 drone flights were carried out, and more than 200 aerial photographs were taken of individual humpback whales. In addition, 34 skin and blubber biopsy samples were collected to determine the sex and pregnancy status of some of the measured whales. The whales encountered included mothers with calves, sometimes accompanied by an escorting male, singing males, and competitive groups. The whales are now migrating towards their feeding grounds around South Georgia, where they will build up fat reserves for the next winter breeding season.