8 August 2012 Last updated at 19:46 ET

In pictures: Humpback whales perform migration spectacle

Humpback whale's tail fin rising from the water, with Sydney cityscape in the background

It’s one of nature’s greatest spectacles as a magnificent procession of humpback whales passes along Australia’s east coast on an annual 10,000km migration from Antarctica to tropical breeding grounds. (Words by Phil Mercer, pics from Whale Watching Sydney)

Hump back whale flipping backwards into the ocean while spectators watch from a boat

Sydney has a front row seat as frolicking pods travel north, and the hulking shapes can be seen from the city’s beaches, cliffs and boats. Within yards of these tourists, a huge adult humpback the size of a bus launches itself high out of the sea off Sydney’s North Head, before crashing down in a mass of foam and spray. It is a mesmerising show.

Spectators in a boat watch a humpback whale in the ocean

A record-breaking number of whales, about 15,000, is expected to pass along Australia's east coast between May and November as humpbacks continue their long recovery from commercial hunting that was banned almost 50 years ago. It is estimated that when whaling stations shut in 1963, the coastal population of humpbacks had been reduced to a little over 100 animals.

People reach put to a humpback whale in the water

Each year, the number seen cruising in waters off Sydney is thought to be increasing by about 10%. Although humpbacks face a range of threats, including climate change and pollution, there is optimism that the species will continue to rebound from the exploitation of the past.

Will Ford, a director of Whale Watching Sydney, says the mammals’ extraordinary trek was delayed this year by the El Nino weather pattern, but they have returned in greater numbers. “They start down in the Great Southern Ocean around Antarctica, which is where their feeding grounds are in summer time, and over two or three months they will swim all the way from that area all the way up to the tropics, so almost a quarter of the Earth’s circumference.”

“The amazing thing is most of the whales won’t eat on that whole migration, so they are doing it all basically on an empty stomach,” says Ford. About 40 species of whales and dolphins have been found in Australian waters.

The carcass of a male sub-adult humpback whale washed up at New Port Beach overnight at Newport Beach overnight on 1 August 2012 in Sydney, Australia.

The migration doesn't always go smoothly - this carcass of a humpback whale was found washed up in an ocean pool on Newport Beach in Sydney this month.

Australia has become a vociferous critic of Japan’s scientific whaling programme in the Antarctic, which Canberra believes is simply a front for commercial hunting. The Japanese target minke and fin whales, and not the humpback. Australia is taking legal action in the international courts to stop Japan’s whaling activities.