Peering into the sound lab
The acoustics team in the 'sound lab' is the hub of the Antarctic blue whales voyage. Our five acousticians share shifts so they can operate 24 hours a day, seven days of the week. In the tiny space festooned with cables they record whale songs, with two screens displaying the sounds characteristic of Antarctic blue whales: calls at 26 Hz, featuring up-sweeping and down-sweeping tones. One night the acousticians called me in ‘Hey, listen in the headphones, there's a really loud call.’ I was captivated by the sonorous tones coming in real time from the ocean depths. Later, out on deck, we watched four Antarctic blue whales feeding at the surface.
The normal routine for our passive acoustics work is to launch a sonobouy at regular intervals. In the sea, the float is activated and the VHF transmissions commence. Once a whale is detected, a second sonobuoy may provide a cross-bearing to guide the ship to the position of the whale.
After visual confirmation, we close in on the whale and launch the inflatable boat to get close enough to the animal to for photo-identification and gathering biopsy samples. The data from our suite of non-lethal methods are integrated in mark-recapture statistical analysis to estimate the abundance of the population.
During the initial two weeks of the voyage, more than 500 hours of audio and about 11,000 calls have been logged. When the voyage returns in March, it will take months to fully analyse all these calls. This voyage is the first time that passive acoustics have been used with the aim of increasing the encounter rate with the rare Antarctic blue whales. Our lead acoustician, Dr Brian Miller, describes the effectiveness of this method on our voyage as 'a success beyond my wildest dreams'.