By RICHARD SHEARS

Last updated at 11:51 04 June 2007

Blasting out of the water like a giant torpedo, this was the astonishing moment when 40 tons of humpback whale decided to give an air show.

Its flippers stretched out like wings as it hurled itself towards wildlife photographer Ray Alley - who fortunately had his camera at the ready.

Mr Alley was on board a tourist whale-watching boat off the coast of New South Wales when he caught these shots of a lifetime.

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"Never before have I seen a whale turn itself towards a boatload of tourists and virtually grin at them as it breached," he said.

"I looked through the lens and saw it flying straight towards me. Usually when a whale breaches they have a habit of doing it with their backs towards you or, if you're lucky, side-on.

"But this one came straight on, as if he knew we were all watching."

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At this time of year, the start of the southern hemisphere winter, humpbacks make their annual migration from Antarctica to warmer waters closer to the Equator to breed or give birth.

"The 30 or so tourists on the boat with me, who were visiting from as far away as England and America, whooped with excitement and who can blame them?" said Mr Alley.

"They had never seen anything like this in their lives before and it's extremely doubtful whether they ever will again.

"When he came down, like a jumbo jet landing hard, he sent water up everywhere. Whether you want to believe it or not, you couldn't help thinking that he was showing off to us."

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When a humpback breaches, it generates more power than any other act performed by a mammal.

Sheila Anderson, of the Natural Environment Research Council, said: "They go down to a low depth and move their tail flukes up and down very quickly to get up the speed to propel themselves out of the water."

The whale then travels close to the surface and parallel to it, before jerking upwards at a speed of 25ft per second.

Around 90 per cent of the body clears the water before the whale turns to land on its back or side. 'Belly flops' also occur but are less common. Scientists do not really know why whales breach.

But one of the main theories is that it is for social reasons, such as exhibiting dominance, or communicating with other whales in a group.

It is also possible that the loud 'smack' upon re-entering the surface is useful for stunning or scaring fish.

Another theory is that a breach allows the whale to breathe in air which is not close to the surface of the water, and so may aid breathing in rough seas.

A further, widely-accepted possible reason is to remove parasites from the skin.

But younger whales breach more often than older ones, and are more likely to do so when the water is choppy. So perhaps they just do it for fun.