IT IS said that the blue whale lights up the sea. Now, Australian scientists have turned to sound to illuminate the hidden lives of the few remaining largest animals on Earth.
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Devastated by 20th century industrial whaling, the blue is seldom seen today. When it does appear, the way the giant's skin brightens surrounding ocean still transfixes those who see it.
''What's fantastic is when it rises for a breath,'' Mike Double, a zoologist at the Australian Marine Mammal Centre, said. ''You see this blue glow, this beautiful turquoise blue glow, under the water before they surface. That's the most magical thing.''
Working off Portland, Victoria, a team led by Dr Double is having more of these glory moments than ever before, using Defence surplus submarine-tracking sonobuoys to reliably find blues by homing in on their song.
Time and again these 9-kilogram cylinders, bobbing at the surface and trailing an underwater hydrophone, have returned to their expedition ship the low frequency hum that is the song of the blue.
''We've seen blues almost every day we've been out,'' Dr Double said. ''We're able to drop our sonobuoys and work in off the bearings to where they intersect.''
The result lifts prospects of finding the largest of them all, the ''true'' blues of the Antarctic. In the 1920s these were recorded to have grown up to 32.5 metres in length and weighed 160 tonnes, making them larger than today's B-double truck.
Hunted down to a few hundred individuals by the early 1970s, there might have been 1700 true blues around Antarctica in 2004, the University of Washington zoologist, Trevor Branch, calculated.
He cautioned there was great uncertainty about the numbers, and in 30 years of International Whaling Commission sightings surveys, only 200 have been seen.
''It seems that they were hit so hard, they are taking a really long time to recover,'' the Australian Antarctic Division's acting chief scientist, Nick Gales, said.
But with the sonobuoys, scientists plan to use the true blues' song, which can travel for about 200 kilometres, to home in on these animals for the first time.
''It's working beautifully off Victoria,'' Dr Gales said. ''So it should greatly increase our chances of finding them in the Antarctic. If we find them we can try to identify individuals through their distinctive skin mottling, take photo and biopsy samples, and on a subset we'll put satellite tags.
''We need to answer some basic questions. Does their population segregate out like humpbacks in winter? Where on earth are their breeding grounds?''
Next summer scientists from eight nations will begin a multi-year blue whale project to find out.
