The opportunity was there, too, with enormous whales breaching with powerful leaps, in a promising opening of the whale-watching season.

The fierce sou'-westerly whipped up white crowns on waves across Twofold Bay at Eden, like a conductor revving up a symphony orchestra for the 40-tonne whales' sudden surges.

Wheeling shearwater birds and slow, wide-winged albatross set the stage in every direction around us on the upper deck of Cat-Balou, a cruiser cutting through the wind chop. Beyond the bay's heads a tell-tale plume of white spray was spotted. Then a humpback mother and her calf and an escort whale's glistening, silver grey backs rose above the surface as they headed south to the Antarctic.

Then, after an hour of Cat-Balou's 330-horsepower engine throttling ahead and slowing to a gurgle as more whales appeared, the promise of something extraordinary.

From the dark depths came the breaching whale, its bright white underside leaving trailing veils of spray, as it rose almost vertically up, up and then twisted like a purposeful gymnast.

"Hooray!" a whale watcher yelled amid rejoicing, whistle blowing, clapping, feet stamping and more urging from the cruiser's deck: "Come on whales. Come on whales.''

Humpbacks are coming down Australia's east coast in overall numbers estimated at 15,000 and rising 12 per cent each year according to Rosalind Butt, who runs Cat-Balou with husband Gordon.

''Yesterday they were spy-hopping - that's when they stick their heads right up out of the water. Some days they do it so close you can almost touch them,'' Mrs Butt said.

''They are being sociable, checking out what's happening. Some have really bad breath.''

Eden's whale festival from October 26 to November 3 will celebrate the humpback and other whales' southern migration.

Currents from the east coast and Bass Strait, mixed with nutrients, are dominated by humpbacks, which hold the seaside town's hopes of a tourist-led revival.

There are plans to extend the port for cruise ships and more freight for the Bass Strait oil fields and Monaro wind farms.

Whales are becoming more prolific. Marine scientist Dave Donnelly said that as the east coast current moved south it drew warm water off the surface, pulling it out to sea. ''As the warm water leaves, the cold water pushes up, bringing nutrients to the surface, including zooplankton and krill. That encourages fish feeding and whole food chains, sharks, seals, birds and whales.

''There's something else going on as well. We have documented 21 species of whales and dolphins, one of the highest densities of a variety of species anywhere in Australia that I am aware of.''

Mr Donnelly said females travelling with calves attracted killer whales and occasionally reports came of orcas attacking humpbacks.

When Mrs Butt first saw whales feeding in Twofold Bay in the early 1990s, scientists doubted her, believing they fed only in the Antarctic, until overwhelmed by the evidence. Researchers have identified 5000 whales on a database