IM HOVERING ON THE SURFACE in Tongas Haapai group with a pair of courting humpback whales. A few metres away, a bus-sized behemoth glides below the waves with a flip of its fluke. Its companion follows. They slip under me, sleek as submarines, and vanish into the deep.
     I stare downwards. The suns rays shimmer up from the depths below. I scan the surface for signs of the whales, but there are only the other snorkellers in my group, bobbing like corks in the sea.
     Two thunderous blows erupt from behind me - the whales are diving again. This time I join them. I take a deep breath through my snorkel and slip silently below the surface.
     As I fin down to 10m, one of the whales rolls on its back, exposing its bright white underside, its massive pectoral fins flared out like wings.
     I surfaced for a much-needed breath and to watch the show unfold. The whales travel in tight arcing loops; they swim belly to belly, embracing each other like ballroom dancers; they twirl inverted, tails towards the surface.
     I dive down again. The larger of the two whales moves in close, barely an arms length away. It rolls until its big dark eye meets my gaze. We hang in midwater, our eyes locked, and for a brief moment I sense some connection with a creature ancient and wise. I feel welcome in its underwater world.
     The South Pacific kingdom of Tonga is one of the only places on the planet where tourists can swim with humpback whales. Laws prevent swimming with the whales in most other countries they visit.
     From July to September each year, the humpbacks migrate to Tonga to mate and bear their young in the island-nations warm, sheltered waters. Since the early 1990s a small but controversial whale-swimming industry has developed. Centred in Tongas Vavau group, seven operators offer snorkelling excursions with the whales, mainly mother and calf pairs.

Hoping to avoid the crowds in Vavau, I booked on a nine-day charter to the less-visited Haapai group on the liveaboard dive vessel Naia, a 36m iron-hulled motorsailer that sleeps 18 and is based in Fiji.
     Since 1996, the Naia has organised expedition-style trips to Haapai to coincide with the peak of the humpbacks migration.
     For the past three days, my underwater encounters with the whales had been fleeting at best. The routine was getting tiring: scan the horizon for blows; steam towards a whale; hope the whale is curious and approaches the boat, don snorkelling gear and enter the water; watch the whale swim away.
     It is with great reluctance that I squirm back into my cold, clammy wetsuit. Free-diving to 10m, I hear the songs of the humpback whale: low, guttural groans, long-winded whines, melodious moans. Its a serene serenade audible only at depth.
     I remember listening to humpback whale songs as a child in the 1970s, on a vinyl record my father got from a subscription to National Geographic. The haunting beauty of the songs captivated me even then.
     Humpback whale songs, which are performed only by males and only during the mating season, are the longest and most complex in the animal kingdom. They can last for more than 20 minutes and be heard up to 20 miles away.
     The song probably contains some sort of information about the fitness of the singer, says Michael Noad, who is a marine mammal acoustics expert at University of Queensland. He says that all males in the same area apparently sing the same song.

Humpback whales (Megaptera novangliae) average 15m in length and weigh up to 40 tonnes when fully grown. They feast on up to 2 tonnes of krill per day during the Austral summer in Antarctica.
     Fattened with blubber, they travel to tropical Pacific islands to breed in the winter months, making a nine-month, 6,200 mile round trip without feeding.
     During that migration, whaling stations in Australia and New Zealand reduced humpbacks to near extinction earlier last century.
     In 1966, when commercial whaling was finally halted, fewer than 250 whales remained from an original Tongan population of about 10,000.
     Subsistence hunting in Tonga further threatened them until 1978, when whaling was prohibited by Royal Decree. Today the Tongan humpback whale population is estimated to be about 700.
     Although whales are currently well protected in Tonga, that protection may be tenuous. To Tongans, whales are food, says Pau Likiliki, Policy and Planning Officer for the Tongan Ministry of Fisheries.
     From his desk in the corner of a cluttered, shared office in the capital of Nukualofa, he explains that whales are a traditional food in Tonga and have been hunted there for thousands of years. Many older people talk about how good whale meat tasted. I think a lot of people want to see whaling reopened.
     In 1999, shortly after the pro-whaling World Council of Whalers visited Tonga, a humpback whale was accidentally killed by a ship strike. The dead whale was towed ashore, butchered and distributed to thousands. A senior government official was reported to have said: It was delicious.
     One of the greatest threats to Tongas whales may be Japan, which has consistently exploited loopholes in the International Whaling Commissions (IWC) ban on commercial whaling.
     Japan publicly acknowledges that it uses overseas aid in developing countries as a means of gaining support in the IWC for its whaling activities.
     Using this method of vote-buying in several Caribbean countries, Japan has been able to repeatedly kill the Australian and New Zealand proposal for a South Pacific whale sanctuary. In 2001, Japanese officials visited Tonga and discussed whaling and aid at the same meeting. The offer was rejected by Tonga.

Its important that there is a strong alternative to whaling, says Rob Barrel, 46, who runs Naia Cruises. He believes that a whale swimming industry is vital to protecting Tongas humpbacks. Tonga could not sustain topside-only whale-watching.
     He says that there are other, more accessible, countries such as Australia and Hawaii which have whale-watching industries that are better developed. He fears that if anything happens to King Taufaahau Tupou IV, who is 85, the royal decree may be reversed.
     A 1999 study by the South Pacific Regional Environmental Program (SPREP) indicated that whale-watching brings in US $600,000 per year to the Tongan economy.
     Whaling profits hardly ever flowed back to the Pacific, says Sue Miller, Biodiversity Officer for SPREP. But whale-watching is plainly an increasingly important part of Tongas economy.
     Some worry that the whales may be paying too high a price. The major concern with swim-with-whales programs is that we know very little about the real impact that such programs have on the whales, says Lesley Gidding, Marine Campaign Officer for IFAW, Asia Pacific.
     Potential impacts may include harassment, stress, behavioural changes, separation or disturbance of mother and calf pairs and physical harm to either whales or humans. There have been very few studies on this.

Conservation groups working in Tonga have adopted a neutral position on whale-swimming, preferring to develop regulations to minimise impact on the whales.
     The guidelines prohibit use of scuba, limit the number of swimmers in the water and set minimum approach distances for boats. But they are not law, and the judgment of the tour operator prevails.
     Most controversial is the practice of swimming with newborn calves. Barrel is sensitive to the stress this can cause and prefers swimming with adult whales. But in Vavau, where the whale-swim industry began, most operators target mother-and-calf pairs.
     My experience in Vavau is worrying. Aboard Whalesong, a boat run by Sailing Safaris, my guide explains the strict swimming guidelines and says that the whales are very comfortable around people.
     But once we enter the water, the mother, which has been sleeping, awakes, and with her calf alongside tries to evade us.

After several swims over a 45-minute period, we finally move on and another vessel moves in. Ours is the third boat to swim with them that morning. On another Vavau charter, I encounter a lone calf, separated from its mother. If it does not rejoin her soon, it will die.
     There have been no published studies that show that swimming changes whale behaviour, says Filipe Tonga, a serious 33-year-old native Tongan who is reported to have started the whale-swimming industry in Vavau and is one of its staunchest supporters. We know when a whale is not happy and we back off.
     Over Ikale beers in the Mermaid Bar, a popular yachtie club on Vavaus waterfront, he tells me how in 1992, while working as a guide, he had the idea of trying to swim with humpbacks.
     At first it freaked me out, he recalls. But he soon felt welcome in their world and began leading others. He is now the IFAW and Whales Alive rep for Tonga. Every year the whales are getting more friendly, he added.
     In Haapai, the two amorous whales are still performing. But after half an hour in the water, even the fittest of us cannot keep up. I retreat to the refuge of the RIB with the others.
     Cold, wet, exhausted and grinning, we motor back to the Naia as one of the whales launches itself skywards, piercing the horizon with a tremendous splash of white.

Tonga is one of the only places where tourists are permitted to swim with humpback whales, although scuba-diving with them is not allowed


GETTING THERE: Tonga is situated in the South Pacific about 440 miles south-east of Fiji. You can fly there from the UK via Manila in the Philippines and Auckland in New Zealand. A 30-day tourist visa is granted free on arrival.
WHALE-SWIMMING:Naia Cruises, 001866 7765572, www.naia.com.fj.
ACCOMMODATION : Theres a wide variety of choice, including serviced apartments, hotels, guesthouses and resorts.
WHEN TO GO : Tonga has a very mild climate, though the winter months can get chilly. From late July until late September, water temperature averages 22-23C, and this is the time to see humpback whales. Visibility averages 30m.
LANGUAGE : Tongan, but English widely spoken.
CURRENCY : The paanga.
HEALTH & SAFETY : Tonga is a very safe country and there is no malaria.
FURTHER INFORMATION: www.tongaholiday.com/whaling.htm.