Scientists using underwater listening devices have made the first long-term recordings of sperm whale calls off East Antarctica, as the marine mammals hunt their prey.
Australian Antarctic Division acoustician, Dr Brian Miller, and consulting ecologist Dr Elanor Miller, used custom-designed and built acoustic moorings to record the whale vocalisations over six years.
They discovered thousands of hours of loud ‘usual clicks’, which have a regular beat that the whales use to echolocate prey such as fish and squid.
“This is the first study to directly measure the seasonal presence and daily behaviour of sperm whales in Antarctica,” Dr Brian Miller said.
“The recordings show that adult male sperm whales forage in Antarctic waters in summer and autumn, and depart the region once heavy sea ice sets in over winter.
“We also found the whales predominantly foraged during daylight hours and were silent at night, possibly due to the availability of their prey.”
The researchers developed a computer algorithm to trawl through more than 46,000 hours of underwater sound recorded at three sites off East Antarctica, to identify the distinctive sperm whale clicks.
“Sperm whales have four types of vocalisations — slow clicks, usual clicks, creaks and codas,” Dr Brian Miller said.
“Slow clicks and codas are thought to be linked to communication, while usual clicks and creaks are linked with echolocation and foraging.
“Usual clicks are produced about 80 per cent of the time the whales are underwater, which makes the whales ideal subjects for acoustic monitoring.”
The acoustic moorings used in the study were designed and built by the Australian Antarctic Division’s Science Technical Support team.
Electronics Design Engineer, Mark Milnes, said the two-metre-long moorings use a hydrophone to detect and record ocean sounds.
“We’ve employed some extreme engineering design to ensure the moorings can withstand 0°C water temperatures at depths of up to 3500 metres, while recording sound continuously for more than 12 months.”
Scientist say as the technology continues to develop, their ability to glean information from the underwater recording devices will improve.
“These studies are an important stepping stone for measuring the number of sperm whales using Antarctic waters,” Dr Miller said.
“Sperm whales are a key predator in the Southern Ocean ecosystem and this work will inform environmental management decisions for this vulnerable species.
“This is frontier science and it’s exciting. We’re hearing things that have never been heard before.”
The research was published recently in Scientific Reports.