Sshhh! The Whales are Courting Below

by Vanessa Gould

The West Australian 4 October 1999

Wind, waves, rain, marine animals and boats make the ocean as noisy for whales as a busy city street is for humans, according to marine bio-acoustician Rob McCauley.

In his 1996 study of the impact of vessel noise on humpback whales in the whale-watching area of Hervey bay in Queensland, Mr McCauley found the speed of the vessel was the biggest influence on underwater noise likely to bother humpbacks. Some big catamarans were very noisy, particularly as their engines needed to constantly manoeuvre to stop drift while whale-watching.

But the impact on the whale was as much related to a sudden change or increase in noise - such as a revving engine - which indicated to a whale a rapidly approaching vessel and the danger of collision.

Mr McCauley, research fellow at Curtin University's Centre for Marine Science and Technology, said the humpback's song was so complicated that high-frequency parts would travel only a few kilometres, while powerful, low-frequency moans would travel many tens of kilometres. Singing, by males only, was assumed to be courting behaviour. "They really blast each other with these songs because a singer will follow a female and be only 20m away and the signals are so loud you can't get in the water," he said. In Hervey Bay, Mr McCauley's team followed a bull they dubbed "the song master". It appeared to teach the song to a one-year-old yearling which kept making mistakes.

Mr McCauley has studied the effects of seismic surveys on marine animals for almost four years. These surveys are used as part of exploration in the petroleum industry. Air-guns fire high-intensity bursts into the seabed to calculate depths of layer from reflected sound. His North-West research, funded by the Australian Petroleum Production Exploration Association, found no indications of stress when monitoring the humpbacks' movement patterns and blow-rates. When the whales were migrating in offshore waters, they tended to avoid an operating seismic ship - which could have 24 to 30 air-guns - at about 3km but it did not appear to change their general migratory pattern.

The humpbacks responded, however, to a much lower level of sound - a single air-gun - in Exmouth Gulf, presumable because they were resting, courting or socialising. Although pods containing females consistently avoided the single air-gun, single animals - probably all males - approached the air-gun, circled the vessel and swam off. The researchers discovered the sound made by a humpback when it crashes into the water after breaching was "uncannily like an air-gun signal".

[Courtesy: The West Australian]