Bonney Upwelling acoustic expeditions 2012
Development of acoustic methods for real-time tracking of blue whales
The Australian Antarctic Division and Australian Marine Mammal Centre conducted two voyages in January and March 2012 in Northern Bass Strait to develop techniques for locating endangered blue whales.
By using sound rather than sight to initially detect the whales, the scientists significantly improved the likelihood of finding and counting whales in the vast Southern Ocean. These techniques were being tested for use on the Antarctic Blue Whale Project, a flagship project of the Southern Ocean Research Partnership (SORP).
The voyages, departing and returning to Portland, Victoria, spent a total of 20 days at sea. An account of the science conducted can be read in Listening to the blues (Australian Antarctic Magazine, Issue 23, December 2012).
During the twentieth century, some 330,000 Antarctic blue whales were killed, first by shore-based operations and then by the pelagic catcher and factory ships. Close to extinction, in 1964 the International Whaling Commission banned the hunting of blue whales, although they were still caught by illegal whaling operations until 1973. The Antarctic blue whale project is undertaking research to better understand Antarctic blue whale recovery from near extinction. The project will do so by developing survey protocols and analysis methods that will lead to circumpolar abundance estimates and provide an insight into the general ecology of Antarctic blue whales in the post-exploitation period.
One of these new survey protocols utilises the fact that blue whales make powerful vocalisations that travel long distances underwater. Blue whale sounds can be heard over distances much greater than blue whales can be seen. With the proper technology, blue whales can be located more efficiently by listening for their distinct sounds.
Currently, there are two subspecies recognised to occur in the Southern Hemisphere: the Antarctic (or true) blue whale (Balaenoptera musculus intermedia), and the pygmy blue whale (B. m. brevicauda). The pygmy blue whale tends to be smaller (maximum length around 24 m) and predominantly remains in lower latitudes throughout the year. The 2012 Blue Whale Voyages were conducted in the Bonney Upwelling of Northern Bass Strait, a known feeding ground of pygmy blue whales. This local feeding ground provided an opportunity to test and refine acoustic tracking methods prior to an Antarctic voyage where the price of ship-time is at a premium.
The aims of the 2012 Blue Whale Voyages were to:
- characterise new acoustic instrumentation for locating blue whales in real-time
- assess practicality and performance of acoustic tracking
- integrate acoustics tracking with photographic and genetic identification research.
A real-time acoustic tracking system was developed and tested for the 2012 voyages. This tracking system was made possible with the provision of DIFAR (directional) sonobuoys by Australian Defence. Directional sonobuoys are typically used by defence forces for tracking submarines, however scientists at the Antarctic Division wrote specialised tracking software and followed protocols that effectively repurposed the sonobuoys for tracking blue whales.
Sonobuoys were deployed throughout the voyages, and scientists used the tracking system to acoustically locate dozens of groups of whales with a success rate of over 90%. During the 20 days at sea, there were over 100 sightings of blue whales, and 49 whales were photographically identified. Photographic identification makes use of the patterns of mottling and the shape of the dorsal fin as a unique ‘fingerprint’ to identify individual whales. Both the real-time acoustic tracking system, and photographic identification are becoming key tools in determining the circumpolar abundance of blue whales in the Southern Ocean.