The acoustic team on Song of the Whale will be trying to find Southern right whales – by listening to them. Maximising our opportunities to work with right whales is key to the success of the project, but first we need to find out where they are. Obviously we can search for them visually, but they need to be close enough, the weather needs to be good enough, and there needs to be enough daylight to allow us to find them.
But finding whales acoustically doesn’t need daylight or calm seas – just hydrophones (underwater microphones). Whales and dolphins use underwater sounds to help them navigate, communicate and find food. Baleen whales make a range of low frequency vocalisations which sound like moans and groans to us. If we can listen in on these sounds, and work out what direction they are coming from, they can lead us to the whales themselves.
But how do you listen for whales? Over the last few years, as part of a team from the Australian Antarctic Division (AAD), we have been developing a way of using military technology designed to locate submarines to instead listen for whales. These devices, called DIFAR sonobuoys, contain underwater sensors which detect sounds but also have a magnetic compass for determining the sounds’ direction. The military deploy them from planes and helicopters to listen for submarines. We can launch them from a research vessel to listen for whales. The sonobuoys then transmit their information back to the vessel by radio, where it is decoded and analysed onboard using specialist hardware and software. We listen to the sounds, identify the whale species we are hearing and plot the direction they are coming from.
We first tried out this methodology with AAD in the Antarctic almost five years ago. Our target species was Antarctic blue whales, and we were very effective at finding them, tracking whales from hundreds of miles away and gradually, by deploying sonobuoys and plotting their bearings, getting close enough to the animals to see their large powerful blows on the horizon, which finally led us to them.
We have now used this methodology to find blue whales on three Antarctic voyages, significantly raising our encounter rate over what would be possible just by trying to locate animals visually. But we’ve been acoustically detecting other whale species too. Their vocalisations are not as loud, and do not travel as far as blue whales’, but fin whales, humpback whales and sei whales can all be detected by our sonobuoys.
So now we are setting our sights on Southern right whales off South Georgia. As with other baleen whales, right whales’ vocalisations are detectable by our sonobuoys, allowing us to find whales whatever the weather so that when conditions allow, we can make the most of our research time in South Georgia.