Researchers have uncovered a language used by migrating whales off the Australian coast. Thousands of hours of humpback whale sounds recorded off Queensland have revealed a vast repertoire of social sounds. From Sydney, Phil Mercer reports.

Australian scientists believe an array of what sound like squeals and grunts are really complex conversations among humpback whales.

Over three years, the scientists identified at least 34 distinctive sounds made by these remarkable ocean creatures.

Some of the calls are very brief, lasting less than one second. Others persist for more than 10 seconds.

Researchers say they had expected to find a handful of recurring noises. The discovery of more than 30 has come as a surprise, and it suggests the humpbacks' way of communicating with each other is far more sophisticated than previously thought.

Rebecca Dunlop of the University of Queensland believes the different sounds are tailored to a variety of social settings. She says some sounds represent aggression, while others indicate warmth and close social ties.

"You get particular sounds called 'whops' that are mainly used by, say, between mum and calf groups ? So mum's saying, 'I'm over here,' and calves answering, saying, 'Yep, I'm over here,'" said Dunlop. "And then there's other sounds that are used in competitive groups when a lot of males are fighting for the attention of a female, and they tend to use lots of high cries - so very high frequency sounds and these low, harsh, aggressive sounds that sound a bit like underwater blows."

The research into migrating humpbacks was conducted about one kilometer off the coast of Queensland, north of the state capital, Brisbane.

The unique sounds have been recorded using an underwater microphone attached to a buoy.

Scientists have said that while only male humpbacks perform the famous whale "song", the social noises and cries are made by all humpbacks.

Scientists say marine animals rely far more on sound than their land-based cousins. Sight and smell have limited effectiveness in water.

Environmentalists have complained in the past that populations of whales and dolphins are being harmed by noise pollution caused by ships.