Study to test if whales 'hear' food

Whales have been seen swimming fast for more than a kilometre toward groups of food. Photo / Richard Robinson

Auckland University team heads first research on giant mammals' ability to sense sound waves of prey.

Do whales hear their dinner?

For years, scientists have only been able to hypothesise that large marine creatures such as whales, sharks and dolphins use hearing as a way of locating food.

Now, a research project led by the University of Auckland's Institute of Marine Science will look to confirm what many have long suspected by playing back recordings of prey in the water and tracking how whales respond to them.

The world-first study, beginning next year, has the potential to reveal important insights into the relationship between large organisms and their food sources - and whether noise from humans can be a barrier.

Scientists have shown that sound in the water - which behaves very differently to that through air - is heard and generated in a variety of ways by a range of organisms, from tiny larval crabs to large whales.

"Acoustics within the marine space are really important for many organisms, yet we don't know a lot about how it drives organisms' interaction with their environment," said Dr Rochelle Constantine.

"We're interested in looking at how the larger animals use the acoustic environment, particularly for food, and testing the hypothesis that food patches have specific sound signatures."

She said the sound of "bait balls" of prey, such as schools of fish, could be greatly heightened when a feeding frenzy involving larger fish and seabirds broke out.

"These prey aggregations are important for many marine species but brings them into competition with each other for access to prey," said research leader Dr Craig Radford.

Dr Constantine said whales had been observed swimming rapidly from over a kilometre away toward prey aggregations, "so we're very interested to find out if there are specific acoustic cues they home in on".

The researchers would draw on existing research on whales, which had proved they were capable of hearing at various frequencies.

"We are also interested to look at large fish and sharks as well, to see whether they are using some kind of hearing capability," she said.

To test the theory, the researchers would attach tags to a number of whales and record the sounds they hear as they move around.

"At the same time, we'll use recordings of the sound of prey and play them back under the ocean. We'll control the volume, the kind of sound, and the distance from the animal."

How the whales reacted would inform their study. The scientists also hoped to learn if the sound of human sources, such as ships, masked food patches, and how this could influence food source dynamics.

Sea sounds

*Baleen whales use sound to communicate with each other over distances of tens to hundreds of kilometres.
*Large sharks are known to be attracted by low frequency sounds.
*Small fish can hear the sound of a reef over tens of kilometres away and will swim toward the sound.Jamie Morton science