Scientists have pulled off a daring close encounter with Earth's biggest animal, the Antarctic blue whale, using world-first acoustic tracking techniques.
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An Australian-led international team homed in for the first time on the marine giants from hundreds of kilometres away by listening for their sounds.
Then, in a hazardous operation in icy waters, a team on a small boat sped within metres of the fast-moving mammals, which can weigh up to 100 tonnes, to dart them for scientific data.
Getting close to a 30-metre blue was ''pretty mind-blowing'', said Virginia Andrews-Goff, who fired the darts. ''I was the size of an ant in comparison.''
Dr Andrews-Goff said she fired satellite tags into two blues, and watched for the next two weeks as one swam 2000 kilometres, confirming the species' great range. Others were given biopsy darts that will show whether human pollutants are accumulating. The project underscored the strength of non-lethal techniques, Australian Antarctic Division chief scientist Nick Gales said.
The key to the research was the use of sonar listening devices developed from anti-submarine warfare to find what acoustician Brian Miller said was the equivalent of a needle in a haystack.
Commercial whaling killed about 340,000 Antarctic blues in the last century, reducing their estimated population to a few hundred by the 1970s. Today, perhaps a couple of thousand of the endangered animals roam the ocean, Dr Miller said.
Until now, scientists have had to rely on surveys that travel along measured routes in the hope of encountering blues.
Instead, using sonar to listen for their low-pitched 20-30 second song, Dr Miller said it was possible to hear a blue singing from 1100 kilometres away, and gradually home in on the sound. ''It's a very deep song but all of the Antarctic blues sing the same tune,'' Dr Miller said. ''They have perfect pitch.''
The team left New Zealand in January to work in waters from the Ross Sea region to far south of Tasmania, and analysed 26,545 blues' calls.
As the vessel approached singing whales, Dr Miller's team was able to close in on their positions within a few kilometres by dropping sonobuoys. Visual observers on the boat were able to do the rest, directing the boat close enough for photo identification.
smh.com.au
