Sound science finds Antarctic blue whale hotspots

Australian Antarctic researchers have used underwater acoustic technology to find ‘hotspots’ of endangered Antarctic blue whales in the vast Southern Ocean.

The research, led by the Australian Antarctic Division and published in January in Endangered Species Research, was conducted during a seven week voyage to the Southern Ocean in 2013 (Australian Antarctic Magazine 24: 16–17, 2013).

The Antarctic Blue Whale Project team used directional sonobouys to listen for the whales’ distinctive songs and calls across a 9,300 km survey area.

They identified seven areas of high acoustic activity where they were able to visually sight 84 Antarctic blue whales, take 50 photo identifications, collect 23 biopsy samples for genetic analysis and deploy two satellite tags.

Project leader, Dr Mike Double, said that the whales were clustered together into distinct regions, generating an intense source of low-frequency calls.

‘We encountered seven distinct hotspots for blue whales in our survey area and some of these were detectable from 600 nautical miles (1,100 kilometres) away,’ he said.

‘There was a steady increase in the intensity of song and other vocalisations as we approached these regions, which suggests that these acoustic hotspots may persist for several days, even if individual whales within them may change.

‘This means that targeting acoustic hotspots, even from long distances, is a reliable method for encountering Antarctic blue whales.’

Australian Antarctic Division acoustician, Dr Brian Miller, was part of the 18-strong team of observers, cetacean biologists and acousticians.

‘Antarctic blue whales have very loud, low frequency songs that are distinctive from other populations of blue whales,’ Dr Miller said.

‘Initially we deployed single sonobuoys to establish the direction of the sound, and then as we got closer and the intensity of the sound increased, we deployed multiple sonobuoys to triangulate the whales’ position.

‘This method allowed us to locate whales to within a few kilometres – close enough for our observers to visually sight them.’

The researchers are optimistic their work has demonstrated a new blueprint for future studies of Antarctic blue whales. Their expectations were validated during the most recent blue whale voyage in February this year, when they successfully used the technology to locate large aggregations of blue whales (see Acoustic technology provides insights into blue whale behaviour).

‘Acoustic tracking allows for a fundamentally different kind of survey than those of the past,’ Dr Miller said.

‘It provides a way to stay with a group of whales for as long as they continue vocalising, allowing sampling of as many individuals within a group as possible, and providing time to study their behaviour and ecological linkages.’

Wendy Pyper
Australian Antarctic Division