Drone footage of Raoul Island and video by underwater cameraman Steve Hathaway offer a glimpse into the value of the Kermadecs as a convergence zone for species from both temperate and sub-tropical regions.
New Zealand scientists are getting up close and personal with giant humpback whales in the Pacific Ocean. Geoff Cumming explains why.
If they weren't so committed, you might think these scientists are mad. Perched in an inflatable boat mid-ocean, metres from a humpback whale, it takes skill - and no little courage - to shoot a satellite tracking device into said whale's backside.
"Whales have a large personal space," explains Dr Rochelle Constantine of Auckland University's marine mammal ecology group.
"Once you get within about 20m they either don't mind you being there or they do. To tag them you have to get within about 5m which requires some good boat driving skills and nerves of steel.
"The closer you get the more attention they pay. Some will just sink under the water or gently swim away. Others will give a significant tail-slap on the surface."
A young humpback in action. Photo / Steve Hathaway
She might add that the boats carrying the scientists, photographers and their paraphernalia are about a third of the size of their quarry. Nor is the location, the storm-tossed Kermadec islands, for the faint-hearted.
Similar dedication is needed to get humpback whale biopsies - tissue samples obtained from a surgical stainless steel tip fired from a modified rifle or crossbow. The device bounces off the whale and is retrieved from the water.
"The challenge of getting data is you have to get inside their personal space, so you have to be fast."
Constantine is just back from Raoul Island, the largest of the Kermadecs group 1000km northeast of Auckland. Her hand-picked party of seven scientists spent three weeks chasing humpbacks around our most remote northern outpost, happily declared a marine sanctuary on the day they arrived aboard the charter vessel Braveheart. The research team aimed to gather data on the genetically-distinct humpbacks of Oceania (the Pacific Islands), whose recovery from the carnage of commercial whaling lags well behind humpback populations elsewhere.
The satellite "tags" will allow researchers to track the movement of the Oceanian humpbacks, which split their time between Pacific Islands breeding grounds in winter and summer feeding grounds off Antarctica. With the biopsies, the whales can be DNA fingerprinted - unlocking genetic information from age, sex, family and birthplace to their Antarctic diet.
It's information which should help researchers to better understand these migratory giants and use it to influence policy-making - from fisheries and ocean management to climate change - in the hope of boosting stocks.
The Oceanian humpbacks (among others) pass through New Zealand on their northern migration (sightings are common in Cook Strait and off Kaikoura in June and July) before heading for breeding grounds. They are unerringly faithful; always returning to breed where they were born, ensuring genetically-distinct sub-populations from New Caledonia in the west to French Polynesia in the east. Their migratory ritual stems from the calves spending the first two years of life alongside their mothers. Though their behaviour in the tropics is relatively well-studied, the location - and state - of their Antarctic feeding grounds remains a mystery.
It takes skill - and no little courage - to shoot a satellite tracking device into said whale's backside. Photo / Steve Hathaway
It is thought they feed only on krill and similar small Antarctic species, fasting at their breeding grounds.
Though most humpback populations are no longer endangered, the Oceanians remain on the IUCN Red List. They were a prime target for NZ whalers until illegal Soviet hunting in the early-1960s caused a population collapse. They are thought to number no more than 5000, whereas their East Australian cousins, which migrate between the Great Barrier Reef and Antarctica, have rebounded strongly since whaling ceased - to around 26,000 and growing.
One theory is that the East Australian humpbacks have it easier than the Oceanians, with islands off the mainland and Tasmania offering nutrient-rich waters and resting spots during their migration. The Oceanians, on the other hand, are thought to cross thousands of miles of deep, less productive ocean to get a feed. Few head south via New Zealand's main islands. But they do stop by the Kermadecs, including mothers with calves barely three months old. The Raoul mission promises to fill a vacuum of knowledge on what happens next.
Constantine is the cetacean (whales, dolphins, porpoises) expert whose research has informed policy-making and voluntary efforts to boost the survival prospects of bottlenose dolphins in the Bay of Islands, bryde's whales in the Hauraki Gulf and the few remaining maui's dolphins off the North Island west coast. Her humpback work is part of an international collaboration between scientists, state and conservation agencies - backers for the Kermadecs visit include the Ministry for Primary Industries, the Pew Charitable Trusts, Auckland University, the Australian Antarctic Division, Conservation International and the French Institute of Research for Development.
In 2010, Constantine spent six weeks in Antarctica on the research ship Tangaroa, hoping to find the Oceanian humpbacks' feeding grounds. The only humpies seen, however, were fat Aussies - banqueting on krill off the Balleny Islands. This discovery saw the islands hurriedly added to the new Ross Sea marine protected area. But where were the Oceanians? With Antarctica's ice melt affecting stocks of krill and other humpback fodder, establishing where they go is important. The Tangaroa covered thousands of Southern Ocean and sub-Antarctic miles without finding them. It's suspected they zero in on feeding grounds east of the Ross Sea - as far east, perhaps, as the Antarctic Peninsula off South America. But the costs and logistics of a research trip in that area are extreme - the scientists had to recalibrate.
Underwater cameraman Steve Hathaway offers a glimpse into the value of the Kermadecs as a convergence zone for species. Photo / Steve Hathaway
The seeds for the Kermadecs field trip were sown by DoC staff on Raoul, who - noticing humpbacks breaching or tail-slapping off the island every spring - began conducting visual surveys. This trip has confirmed the scientists' hunch the islands are a meeting point for Oceanian humpbacks before they head south - underscoring the value of last month's announcement extending the marine protected area to 200 nautical miles. Raoul's location at 30 deg S makes it an ecological treasure trove: the waters are a convergence zone for temperate and tropical species. Proximity to the fathomless Kermadec trench affects the water temperature while underwater volcanoes add to habitat diversity.
"There's been 12 nautical mile protection for some years - there's now such diversity of life it's incredible," Constantine says. "You've got tropical fish, hard and soft corals, giant black groper, Galapagos sharks - it's unbelievably beautiful and a meeting place not just for whales but for animals from the tropics and sub-tropics.
"The [sanctuary] declaration is an opportunity for the Government to crank up biodiversity research around our northernmost territory."
Raoul is also about 1000km south of the Oceanian humpbacks' breeding grounds. "It's the furthest south for an aggregation of whales - we are not seeing this at Pitcairn or Easter Island. After that it's daylight until you get to Antarctica."
Even in this sanctuary, the scientists saw reminders of the whales' vulnerability: a humpback they photographed on the first day was later seen with a barnacle-encrusted mooring line draped around it. Seabird activity off one bay led them to a freshly dead calf being pecked at and gorged on by sharks - including a great white which, records show, was tagged off Stewart Island four years ago.
Constantine's biggest fear was returning from the high-cost field trip with little information. But with expert drivers on the two boats, the researchers successfully tagged 25 humpbacks and brought home 85 tissue samples. They also photo-ID'd more than 100 individuals: unique markings on their flukes (the underside of their tails) enable the whales to be identified and catalogued, building the picture of where they come from and where they go.
For the scientists, this is data nirvana. "We went up there excitedly chattering and when we returned [after three weeks on a boat] we were still excitedly chattering." Favourable conditions helped: "It's an island in the middle of a very large ocean - we were very fortunate to lose only 1 days to the weather.
"We were seeing easily 40 whales a day - perhaps one or two thousand whales pass this way in a short, sharp burst of activity. Some whales would hang around for a few days. It's their last chance for a rest before Antarctica, particularly for mums with calves. You'd see them tuck in to some of the bays for shelter.
A great white shark (tagged four years ago off Stewart Island) feasting on a dead humpback whale calf. Photo / Steve Hathaway
"It's highly entertaining. We'd see the calves playing with bottlenose dolphins, chasing and turning in tight circles, sometimes the mums would join in. The calves are 6 to 7 metres long, not the vulnerable things we see on the breeding grounds."
The adult males' behaviour surprised the scientists. "They're just a little more chilled out, coming down from those really competitive behaviours you see at the breeding grounds. It's kind of cool to see all those behaviours dialled back a little.
"But you had the sense they were going somewhere which made the job more challenging. There was more of a sense of urgency than on their breeding grounds where they are more preoccupied."
The mission is already paying dividends: satellite tracking has confirmed the theory that the humpbacks head southeast from Raoul, across thousands of miles of ocean. Such tracking would not have been possible a few years ago - technology has improved so that tags last, and transmit, for longer - important when your subject is swimming at around 6km an hour on one of the longest migrations on the planet.
"With improving technology it actually became feasible that we could tag some whales at Raoul and follow them to their Antarctic feeding grounds."
Constantine and her colleagues on the Great Humpback Whale Trail keenly anticipate discovering exactly where they end up.
The song of the humpback whale is relayed across the Pacific, from breeding ground to breeding ground.
Just as different songs and language distinguish human cultures, each humpback whale population has its own distinct song, even if it's on high rotate. The distinctive sound stems from the whales' habit of returning each year to their birthplace to breed - each humpback population is genetically-different, be it northeast Australian, New Caledonian, Tongan, Fijian, Samoan, Niuean or French Polynesian.
This means song recorded on the Kermadecs field trip, where the Oceanian sub-populations appear to converge, can be compared to the growing catalogue of humpback whale song from across the region to help identify where individual whales come from.
Only males sing, during breeding season and while on migration - offering clues to the point of their song, says Associate Professor Michael Noad, a humpback whale acoustics specialist at Queensland University. Though the songs remain distinct, researchers have discovered that they evolve from year to year - variations like a DJ's remix. Within any population they all sing the same complex song but the song changes over time," Noad says. "All the males in the population keep up with these changes - the theory is that they copy each other's song."
Scientists believe the changes in tune are picked up and spread from population to population, despite the vast ocean miles that separate them.
"What usually happens is that the song starts off in Eastern Australia and makes its way to New Caledonia and Tonga the next year and so on. But by the time it's picked up in French Polynesia the song in Eastern Australia has changed.
"We call it a process of cultural transmission. The song pattern is not something the males are born with, it's part of their learning."
The mechanics of this mix-tape sharing are not fully understood. There's scant recorded song data from the humpbacks' Antarctic feeding grounds. But interaction between populations along migratory routes to and from Antarctica, may play a part.
"In the South Pacific we see some degree of contact between populations, which may explain how the songs are transmitted from one area to another over time."
For instance, some East Australian humpbacks are known to pass through Cook Strait where their song might be heard by Oceanian cousins using that migratory corridor, Noad says. "We don't yet know exactly how the songs are transferred."
This month's recordings at the Kermadecs, made by research scientist Olive Andrews of the South Pacific Whale Research Consortium, will add to the back catalogue.
"We can match the themes to areas as another way of knowing where the Kermadec whales are coming from and going to," she blogged.
