The sight of a humpback whale breaching, only to crash beneath the surface ranks right up there among nature's greatest hits. Many humans identify with their winter lifestyle - wallowing in the tropics throughout their mating and breeding season, spouting forth.

Yet when, last year, the conservation status of these ungainly giants was downgraded from "threatened" to "least concern", New Zealand scientists were not among the cheerleaders.

They knew that the humpbacks which pass through our waters, a distinct sub-population, were far from thriving. Summoning up 20 years of data gathering and research, scientists succeeded in having oceanic humpbacks placed on the endangered list by the International Union for the Conservation of Nature (IUCN).

This week, as the Government was tossing out a bill to improve protection for marine mammals, representatives from a dozen Pacific countries met in Auckland to progress an agreement on the conservation of cetaceans (whales, dolphins and porpoises) in Pacific waters. The Memorandum of Understanding on Pacific cetaceans, agreed in 2006, is under the United Nations-backed Convention on Migratory Species.

The meeting, just the second of signatories to the Pacific MoU, adopted a fledgling recovery plan for Oceania humpbacks being developed by marine scientists. Blue and bottlenose dolphins are other cetaceans whose status in Pacific waters is causing concern, but the meeting's moves on the oceanic humpbacks highlights the scientific unease about their recovery.

New Zealand is in the middle of a migratory corridor for oceanic humpbacks which winter in the waters off New Caledonia, where they breed and rest before heading south to spend the summer gorging on Antarctic krill.

Once a common enough sight off our coast during their winter and summer migrations, humpback sightings remain rare more than 40 years after commercial whaling ceased.

That's not the case across the Tasman, where the genetically distinct east-Australian and west-Australian humpback populations are thriving.

The humpbacks of Oceania - several separate breeding stocks have been identified - are small populations, scattered over nine million sq km of ocean.

They are remarkably faithful - despite mingling with other humpbacks in Antarctic waters; most return to the same breeding grounds each year (although some island-hopping occurs).

Scientists call it maternal site fidelity - calves follow a migratory route learned from their mothers - which explains the development of distinct populations but at the same time makes them more vulnerable to threats.

A report by the South Pacific Whale Research Consortium says most of Oceania's small breeding populations remain at extremely low levels and some are vulnerable to extinction. The overall sub-population is thought to be about a quarter of pre-commercial whaling levels and may take another 50 years to recover.

The humpback's comeback is desirable for reasons ranging from pure conservation and biodiversity values to the potential of whale-watching to boost island economies.

Whale and dolphin-watching is now worth more than US$21 million ($32 million) a year to Pacific island nations, according to the International Fund for Animal Welfare.

But whales also hold strong spiritual and cultural significance to the island populations - their arrival signalling the start of a harvest or other events.

New Zealand marine scientists, including Mike Donoghue of the Department of Conservation and Scott Baker and Rochelle Constantine of Auckland University's school of biological sciences, are at the forefront of efforts to revive the humpback through initiatives such as the Pacific Cetaceans MoU, the recovery plan and continued research.

Constantine says the MoU will encourage such measures as reducing fishing bycatch, habitat destruction and pollution as well as responsible whale and dolphin-watching. But signatories also recognise that fishing is the main source of income for most island nations.

"The challenge for scientists is to offer solutions which allow countries to generate income without disturbing or endangering vulnerable species. Our interest is the science. We can help governments by informing them what's possible. We can also encourage them to engage in data collection," she says.

Just why the humpbacks that call Oceania home have failed to bounce back as well as those elsewhere has puzzled scientists since the early 1990s, when Baker and Donoghue's curiosity about their disappearance from New Zealand waters took them to Vava'u in northern Tonga. The mystery abated only this year with the publication of new research by Oregon State University's Marine Mammal Institute, where Baker is now based.

The study concluded that illegal whaling by the Soviets south of New Zealand from the late-1940s to the early-60s hit Oceania's humpbacks so hard that the population has not yet recovered.

The researchers found data confirming the true number of whales killed by the Soviet fleet - as opposed to fake records created by the KGB, which wildly understated the number of whales taken.

This meant thousands more whales were slaughtered than the number allocated to the Soviets each year by the International Whaling Commission.

The study's authors interviewed four former marine biologists on the Soviet fleet whose correct data was turned over to KGB commissars, who created a second set of books, Science magazine reported in May.

The biologists had to sign a KGB statement saying they would never release their data. But the four spirited away their records and, in the 1990s, began turning over the data to the IWC.

The killing was particularly frenzied in the summers of 1959/60 and 1960/61 when 27,000 whales were killed in Antarctic waters south of New Zealand. Later the Soviets took another 23,000 but reported only 2710 to the IWC, according to Science magazine.

The carnage led to the closure of whaling stations in New Zealand and Australia, the Oregon study reports. Off the New Zealand east coast, the catch dropped from 361 whales in 1960 to 80 in 1961 and 32 the following year.

By the time whaling was banned in the South Pacific, Baker estimates only 15 females of breeding age remained in the waters off Vava'u.

More than 40 years on, they estimate the entire Oceania humpback population numbers just a few thousand. When the scientists lobbied to have these humpbacks added to the endangered list last year, they noted: "What is clear is that any population increases appear to be lacking or very low." The recovery in Fijian waters remains particularly slow.

Part of the problem is that as migratory species any effort to save the humpbacks needs to be wide-ranging. The recovery plan will look at ways to manage threats which range from "scientific" whaling, fishing bycatch and entanglement to pollution and habitat modification, whale watching and climate change.

Constantine says any measures need to be based on sound science. Most of what's known about Oceania's humpbacks comes from photo identification - unique patterns on their flukes (the underside of their tails) distinguish individual whales - genetic data from skin samples, tagging for satellite tracking and analysis of song captured on hydrophones. Public sightings and photos of flukes are highly valued.

But big gaps in knowledge remain. While the researchers have catalogued about 1400 oceanic humpbacks, the population estimate remains vague. And though knowledge of their movement in breeding grounds is building, little is known about their behaviour in Antarctic feeding grounds.

That will change next year when Niwa's research vessel Tangaroa visits Antarctica on a data-gathering mission largely funded by the Australian Government. Constantine will be on board as part of the research team - taking pictures, satellite tagging and collecting samples for genetic analysis.

"Many mysteries remain about their movement in southern waters," she says. "We do know there is some mixing [with other sub-populations] on the feeding grounds. Hopefully we will get an idea of how much lateral movement there is and what happens when they move north."

Meanwhile, work will continue on the recovery plan and efforts to help other cetaceans under the Pacific MoU. Signatories hope to bring other islands on board and Tonga attended the Auckland meeting as an observer. It's participation is keenly sought because it is considered the crossroads for oceanic humpback movements.

Donoghue says the population in Tonga is recovering better than in some island nations and the economic spin-offs are noticeable. Whale watching in the island kingdom is estimated to have grown by 20 per cent each year since 1998.

"For conservation to be successful, especially in small island states, the people have to see the economic benefit from it," he says.

"That's the wonderful thing about conserving whales: a whale that's protected comes back every year; a whale that's harpooned is a one-time payout. Then it's gone."

COUNTING WHALES
* Based on catch records corrected for illegal Soviet whaling, more than 200,000 humpback whales were killed in the Southern Hemisphere from 1904 to 1980. They were hunted along migratory corridors including the coasts of New Zealand and Australia.
* Illegal Soviet takes of 27,000 whales in two seasons (1959-60 and 1960-61) brought about a population crash and the closure of land stations in Australia and New Zealand. Hunting of whales continued in Tonga until 1978.
* Although protected by a Southern Hemisphere ban on commercial whaling since 1963, humpbacks can still be killed for scientific purposes under the International Whaling Convention. Japan recently proposed to kill 50 humpbacks in the Southern Ocean, south of New Zealand and Australia - an area where endangered oceanic humpbacks feed.
* The economic zones surrounding more than a dozen South Pacific countries have been designated whale sanctuaries. The Southern Ocean sanctuary provides an additional layer of protection while in Antarctic waters.
* Humpback whales are vulnerable to entanglement in fishing gear and have been struck and killed by ships.

TINY PITCAIRN JOINS PROTECTION FORCE

News this week that the Pitcairn Islands had signed up to an international effort to protect whales and dolphins slipped under most radars.

But the signature of Governor George Fergusson at the Auckland meeting of the Memorandum of Understanding for the Conservation of Pacific Cetaceans was welcomed by marine scientists around the Pacific.

With a population of less than 50, it's unlikely Pitcairners will take to their boats to patrol their economic zone and thwart any illegal whaling, says Melanie Virtue, inter-agency liaison officer for the Convention on Migratory Species.

Virtue, a New Zealander, works in Bonn, Germany for the convention secretariat - the UN agency behind the Pacific Cetaceans MoU. She was in Auckland for the meeting.

Humpbacks are thought to have started migrating to Pitcairn around 15 years ago and its waters are used as a calving ground.

A 2007 survey revealed around 60 sightings of single humpbacks, mothers and calves.

Eco-tourism is seen as a future lifeline for the British colony.

Pitcairn is the 12th Pacific territory to sign the MoU - ensuring information-sharing about endangered humpbacks and other vulnerable whales and dolphins, and the chance to gain expertise from neighbouring countries, says Governor Fergusson.

DoC's Mike Donoghue says Pitcairn's signature means millions of kilometres of the South Pacific are now covered by the agreement.

"The area covers a lot of small developing states with huge areas of water. Until the MoU came along they were feeling a little disempowered from the international community.

"With the UN backing, they are now part of a family of 110 member countries."

He says many island nations have a strong spiritual and cultural connection to whales so there is great enthusiasm for their protection.

New Zealand and Australia can help these territories to build capacity by providing technical support, laboratories for genetic analysis and research equipment - but it is not rocket science. "If they have a hydrophone and a laptop they can do some really valuable work."

Rochelle Constantine of Auckland University's school of biological sciences says Pitcairn is "probably the most remote place Oceania's humpbacks can be found - it's really exciting they are now part of the MoU".

"It would be ideal to have all Pacific Island countries and territories on board."