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Last Updated: Thursday, 25 March, 2004, 10:15 GMT
Whales' sound fishing trick
Scientists believe they may have solved one of the mysteries of how humpback whales successfully hunt - and their findings may help beat cancer in human beings.

Humpback breaching   Noaa
A humpback shows its paces
It has long been known that some species of whale hunt by creating a cylindrical column of bubbles in which fish are corralled. But until now, no-one knew why the fish had refused to swim out.

However, Professor Tim Leighton, of the Institute of Sound and Vibration Research at the University of Southampton, UK, has said he believes the whales use sound to scare the fish into staying put.

"If sound is propagating through water, the most potent, naturally occurring entity it can meet is a bubble," he told BBC World Service's Discovery programme.

The bubbles slow sound down - a beam of sound aimed towards the bubbles will be trapped, bouncing around within the column at a speed of 1km/s.

"If [the fish] ever try to leave the net, what they encounter is a very loud wall of sound," Professor Leighton added.

'Scary noise'

When humpbacks hunt, up to 30 of them will circle in the deep water, releasing bubbles.

As these bubbles rise to the surface, they create a column, inside which fish congregate. The humpback whales will then swim up from beneath the cylinder and eat the fish.

"We know fish will swim through bubbly water quite happily," Professor Leighton explained.

"I think what is happening is that while the whales are producing this net, they are making a very loud, scary noise.

"As these sounds get trapped within the cylinder of bubbles, the fish stay within the quiet region."

What is more, the startled fish form a tight school, and so make a compact meal for the whales when they rise up from beneath the trap with their mouths open.

There may now be many potential uses for these findings.

Specifically, Professor Leighton said there were many opportunities for using the acoustic effects of bubbles - especially in the arena of modern warfare.

"In the oceans, it is becoming very important because our naval scenarios have moved from being deepwater, where you're looking for nuclear subs underneath the ice caps, to shallow waters like the Gulf," he said.

"[There] are many waves breaking, many bubbles, in which you can hide objects like mines."

'Little injectors'

The research has potential benefits in medicine, too.

Bubbles can be collapsed while inside the body using ultrasound. This makes them potentially very useful in seeking out and destroying dangerous cells.

"We might conceive of one day taking the bubbles and coating their outer surface, so that as they travel through the body they can track down particular types of cells," Professor Leighton explained.

"So we put these bubbles in, they spread though the body, they attach to particular types of cells - perhaps cancer cells - that you want to get rid of.

"Then if we hit these bubbles with ultrasound, we can collapse them."

The bubbles would then act like "little injectors", and whatever was contained within the bubbles would be injected into the dangerous cells to kill them.




SEE ALSO:
Whales drawn to emergency sirens
03 Dec 03  |  Science/Nature
US Navy agrees sonar limit
14 Oct 03  |  Science/Nature
Sonar 'may cause whale deaths'
08 Oct 03  |  Science/Nature
Science in search of the low rumble
09 Oct 02  |  Science/Nature
Doomed love songs of whales
19 Jun 02  |  Science/Nature


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