Call of the deep

Big blue ... a swimmer with humpbacks in the Ha'apai island group.

I'm looking for a song. It isn't music you can download or find in a record store, however. I want to hear a humpback whale singing as he tries to woo a mate.

I'm about 10 kilometres off the coast of the Ha'apai island chain of Tonga, an hour's flight north of the capital, Nuku'alofa, in the company of Australians David and Tris Sheen, who run Whale Discoveries.

Tonga's whale-watching practices are more relaxed than those in Australia, where a 100-metre exclusion zone prohibits any closer interaction with whales and swimming is not permitted. In Tonga, swimmers and snorkellers accompanied by a guide may enter the water and cautiously approach humpbacks. Licensed operators of vessels are allowed within 10 metres of whales when picking up swimmers.

Whales migrate each year from Antarctic waters to the warmer seas of Tonga. About 3000 humpbacks pass through Tongan waters between June and October, and Ha'apai, along with the northern Vava'u islands, are the main areas for interaction.

The Sheens promote "sustainable interaction" as part of their business, believing the more that is learnt about humpbacks, the better the chances of protecting them.

Tonga's waters are usually idyllic, though on this soupy Saturday they're anything but. Rain spits sideways as we head to a coral shelf at Mushroom Rock Bay to look for humpbacks. The sea rolls under a thick cobalt skin and the sky, the colour of smoke, smudges any view of the horizon. It doesn't deter the Sheens, though.

We slice through the swell in a modified rigid inflatable called the Tropic Bird as Dave discusses the whale types in these waters: those that swim away when approached, those that allow swimmers to be near them and those that interact with swimmers.

This isn't an adventure in which the attractions wait around, however. From the inflatable, we see four whales at a distance as we head into the wind, so Dave unravels a sonar device and slings it overboard in the hope we'll hear singing.

Males often sing as a way of advertising themselves to females and showing dominance. Each song can last 12-17 minutes, yet we hear nothing but the gurgle of waves.

We cruise above the shelf for about two hours, looking for the flick of a tail or a puff of water from a breach before Dave slows the Tropic Bird. About 200 metres away, the smoky vapour from a blowhole rises as a whale comes up for air. A mother and calf surface briefly before floating back under like disappearing ink blots. The pair don't move away and the next time they appear, it is closer to our vessel. Dave declares they're comfortable and Tris indicates we should follow her into the water. We stay as streamlined and still as possible as we kick towards the whales; the water around us oily and slick. "Excretions from the whale's skin," says Tris, and I see fingernail-size slivers of skin floating on the surface as we snorkel closer.

Then I see a shape below me, rising, nearing the surface. I take in short, sharp breaths through my snorkel as the shape gets closer. I can make out the fluke, white ridges on the fins and the barnacles on this 18-metre humpback as it floats level with me. I see scars on its belly and metre-long parasitic fish dipping below. For an eerie moment the whale opens its eyes and looks right at me. I gurgle in shock. Just as it nears the surface, I lift my head and watch it leap into the air, flick its tail and thud back under the water in a ripple of swell.

When it descends about 30 metres to a coral shelf, we kick slowly closer. Despite the weather conditions up top, the water here is warm and clear, allowing us to spot a calf in the turquoise depths. Dave has told us calves drink about 500 litres of milk a day and I watch it dance above its mother before surging towards us, spinning and floating in turn along the surface. "It knows we're here," says Tris, as we watch in awe, treading water and taking photos every time the calf approaches.

My hands look as shrivelled as sultanas after an hour in the water watching mother and calf, and my stomach begins to roll with the ocean's swell. With each surge I'm lifted by metres in choppy water, while the calf swims around and under its resting mother.

Then I feel something building from below and blink through my mask. The mother is coming up again for air. By now, however, the swell is so strong, I decide it's time to head for calmer waters.

I'm still looking for that whale song when I fly from Ha'apai to the Vava'u islands and join the crew of a company called Endangered Encounters. It's sunny and calm as we cruise past jungle-covered islands. Then our Tongan captain, Meki, spots a group of whales on a "heat run" - males chasing a female until she is exhausted. The "last man standing", so to speak, will then mate with her. Meki takes our vessel past the empty sands of Kapa Island and into a channel, spotting the telltale sign of a breach. As the boat slows on approach and two whales come closer, I don a wetsuit and slip into the water.

My guide, Brenda Manceau, leads me into the deep and we spot a pregnant mother and her 15-metre chaperone floating across the reef. As they move towards us, I see a school of stingrays zipping along the sandy floor and I'm so distracted that Manceau has to yank me out of the way as a whale rises directly below me. It's just metres away and I watch its fluke vault into the air before it dives. Meki spots two more whales and jumps in with his snorkel. Many Tongans are hesitant about swimming with whales, though this is too good an opportunity.

Meki and I duck-dive and I follow his trail of bubbles as we hear an unusual noise. I've only ever heard it on soundtracks - at the naturopath or a dentist's surgery. It's a whale song drifting through the water.

To my ear, a recorded whale song has always sounded contorted, yet the way in which sound reverberates through the water is beautiful here; the ultimate surround sound. Meki and I listen for several minutes before the whales swim away. It's impossible to tell but I leave these waters hopeful that one male's serenade is a success and he's showing off his moves to a female far below us.

Ben Stubbs travelled courtesy of the Tongan Visitors' Bureau.

FAST FACTS

Getting there

Virgin Australia has a fare to Nuku'alofa from Sydney (4hr 35min non-stop) for about $359, one way. Melbourne passengers pay about $369 and connect in Sydney. See virginaustralia.com. Chathams Pacific has regular flights from Nuku'alofa to Ha'apai and Vava'u; see chathamspacific.com.

Swimming with whales

Ha'apai: Whale Discoveries is based at Tonga's Serenity Beaches Island Resort, Uoleva Island. The tour operator offers diving, snorkelling and whale discovery tours aboard the Tropic Bird or a 41-foot catamaran. A full day with the whales, including all equipment, morning tea, lunch and afternoon tea, costs 275 pa'anga ($150). Tours are run July-October and depart from Foa Island, Ha'apai's Sandy Beach Resort and Matafonua Lodge; see whalediscoveries.com.

Vava'u: Endangered Encounters has day trips and longer journeys including five-day packages for enthusiasts; see endangeredencounters.com.

Staying there

Sandy Beach Resort has 12 comfortable bungalows built on the ocean's edge, where it is common to see whales from balconies. The resort has solar hot water, a bar and restaurant. A double bungalow stay costs from 341 pa'anga a person a night, and includes breakfast, dinner, and Ha'apai airport transfers; see sandybeachresort.de.

Reef Resort is away from the main town on the island of Kapa in the Vava'u group. The resort has four private fales (bungalows) with airconditioning and private decks. The resort is in front of the Japanese Gardens, and reef, snorkelling and kayaking gear are available. From 360 pa'anga a night; see reefresortvavau.com.

More information See tongaholiday.com.