Scientists have answered a mystery of where some of Australia’s biggest whales go to calve, and it turns out the progeny are Indonesian.
The 24-metre giants known as pygmy blue whales, which spend summer in the Southern Ocean, have been closely studied while feeding at hotspots along the Australian coast.
But where they went for winter had been a mystery. Now the whales have been tracked with satellite tags as they dodge offshore oil and gas industry hazards and entanglement in fishing nets on their northwards autumn migration.
They head to the Banda and Molucca seas, east of Sulawesi, where they appear to calve.
The study, by scientists at the Australian Antarctic Division and published in the journal Public Library of Science, is a culmination of years of work developing a satellite tag that sits in the whale’s blubber layer without harming the animal.
Combined with the division’s pioneering acoustic tracking work, the tag has enabled whale scientists to build a picture of the hemisphere-roaming life of a pygmy blue.
"These animals are kind of a different beast from the Antarctic blue," said Mike Double, of the division’s Australian Marine Mammal Centre. "They’re designed to travel vast distances and exploit ephemeral resources."
Dr Double said it appeared the pygmy blues – so named for their shorter tail stocks – fed on krill in the productive waters above the continental shelf break off south-western Victoria and Kangaroo Island.
But one of the best aggregations of the whales was around the Perth Canyon. It was here, offshore from the West Australian capital, that scientists shot satellite tags about 3 centimetres deep into the blubber layer of 11 whales.
The whales hugged the western coast to North West Cape, then took a line for Timor and into the Banda and more northern Molucca seas, where the tags stopped transmitting.
One came to life again months later to show its carrier was back in waters south of Australia in summer.
Dr Double said until this discovery the annual migration of the whales was unknown. Because they are such widely roaming travellers, it is possible they can take other routes.
In the central Banda Sea, where most seemed to congregate and feed on the product of a monsoonal upwelling, in which deep, cold water rises towards the surface, they would not be visible to coastal Indonesians.
As for scientific work in Indonesia, Dr Double said it was ‘‘a black hole of information’’. ‘‘We are certainly open to co-operation with Indonesia, but I’m not aware of any Indonesian whale scientists."