MATING humpback whales have been captured on camera for the first time - and the act is one of amazing gentleness between the marine giants.

Australian photographer Jason Edwards, who took the images off Tonga, was stunned by the "brief but tender" copulation.

While humpback "heat runs" - in which 15m-long, 40-tonne males fight to win a female's attention - have been well documented, and often wrongly described as mating, this is the first time the actual act of copulation has been photographed, the National Geographic Channel said.

"It was amazing. There were four or five males vying for her attention and while the larger ones were busy jostling each other, the smallest one swam away with the female," Mr Edwards said yesterday.

"Their coupling lasted less than 30 seconds, which might explain why it's never been captured on film before.""

Mr Edwards said the female allowed the male to grapple her on a slight angle, sliding in from behind until his belly touched. Placing a pectoral fin over her flank, he stroked her gently during the act. After the pair broke apart, the female released a burst of bubbles from her mouth, rather than through the spout.

"The purpose of this bubble release is still unclear however it may have signalled to the male that the reproductive act was over," Mr Edwards said.

The image taken in the spring of 2010 was kept secret until today while whale researchers constructed their thesis on whale mating. Tonga's humpbacks, like those currently migrating up the Australian east coast for winter, spend summers in Antarctica but take a different route north.

The tender mating act is in stark contrast to recent discoveries that other marine mammals like bottlenose dolphins are capable of rape.

The images are part of National Geographic Channel series Great Australians which screens Sunday at 7.30pm.

Originally published as Tender mating ritual of the humpback