Antarctic marine scientists who have been eavesdropping on the world’s largest creature, the blue whale, have detected individuals singing from almost 750 km away. The researchers, part of a six week Australia-New Zealand Antarctic Ecosystem Voyage on the RV Tangaroa to the Southern Ocean returned to Wellington, New Zealand on March 11.
Dr Brian Miller, an acoustician on board, said directional sonobuoys (devices which are equipped with an acoustic receiver and a radio transmitter that emits radio signals when it detects underwater sounds) were used to listen for the low rumbling song of blue whales and guide the ship to them. “It is really exciting to be able to study these whales in the vast Southern Ocean and hear their calls over 750 km away,” Dr Miller said. “During the voyage we were able to record more than 40,000 calls over 520 hours.”
Australian voyage leader, Dr Mike Double, said after travelling a large distance without sighting any whales, they were staggered to witness over 80 of these rare whales in a relatively small area. “With such a patchy distribution it is only possible to study this endangered species efficiently using the acoustic technology developed by the Australian Antarctic Division”. The scientists photo-identified 58 individual blue whales during the voyage by the specific pigmentation and mottling patterns on the whales’ flanks. These images will help estimate the population size, rate of recovery and movements of the endangered Antarctic blue whales. “Our ability to find these whales and the multidisciplinary nature of the voyage also allowed us to investigate the whales’ habitat.”
Using echosounders, instruments that can determine distances under water by transmitting sound pulses, they were able to map, characterise and monitor krill, the main prey, in the vicinity of the blue whale. They found that swarms were denser than those found anywhere else. “Remarkably, using new advanced echosounders, we were able to track individual krill for the first time allowing an examination of the changing internal structure of the krill swarms.” Oceanographic data that was gathered will also reveal the productivity of the waters.
The voyage which was a collaboration between Antarctica New Zealand, the New Zealand National Institute of Water and Atmospheric Research (NIWA) and the Australian Antarctic Division, will “have an enduring legacy for the science community and the understanding of the unique ecosystems“ Dr O’Driscoll, the New Zealand voyage leader, said. “It’s not just about finding whales, we now have a much greater understanding of the big picture – the ecosystem – on which the top predators depend. When all the data from the voyage have been analysed we will have an improved scientific basis to understand impacts on the Southern Ocean and its inhabitants”.
Source: National Institute of Water and Atmospheric Research (NIWA), Australian Antarctic Division (AAD)