This new year pilot whales have again thrown themselves ashore on Farewell Spit. Andrew Stone investigates what can be done to help the mammals seemingly determined on killing themselves

"Last night," ranger Mike Ogle said, "things went better."

By better, he meant just one pilot whale out of 49 that volunteers had nudged back into the rising Golden Bay tide had returned to shore to die. It was the only break that Mr Ogle, other Department of Conservation staff and dozens of volunteers had enjoyed in the first few days of the new year after spending many distressing hours struggling to keep stranded animals alive.

The task was demanding, even dangerous. One ranger was bruised when he was hit on the arm by a whale flipper. For the whale savers, many of whom had spent long uncomfortable hours clad in wetsuits, bucketing seawater over the creatures and tipping their two-tonne mass upright to release pressure on vital organs and flippers, the relief of saving the whales was palpable.

It looked touch and go for several hours as refloated whales "milled around" offshore, seemingly on the brink of making a decision. By morning it appeared the animals had chosen to head towards open waters because they were nowhere to be seen.


Said Mr Ogle: "We can't save every one but there's a feeling of immense satisfaction that this group seems to be staying offshore."

Since New Year about 40 pilot whales have died on the 27km long sandy hook, mostly at the southern end of the spit in area called Triangle Flat. Among them were females with calves.

Rangers shot the stricken animals after the unpleasant decision to euthanise the whales was made, despite desperate efforts to encourage the mammals to hang on for Golden Bay's returning tide. Vital signs in many of the stressed animals were fading, their life support systems shutting down, their hides burned from hours exposed to the sun. DoC staff were left with no other option but to put the whales down.

The outcome was sad, Mr Ogle said, but could have been worse had volunteers not responded to pleas for help.

Each summer the scene is familiar: the arc of Farewell Spit which encloses the stretch of water bay the Dutch explorer Abel Tasman named Murderers Bay becomes a graveyard for pilot whales. Yet the reality is that hundreds of whales die around the New Zealand coastline each year. The toll is high because as many as half the world's cetaceans travel through the waters around New Zealand. By the time they wash ashore, many are already dead, especially when a single animal is involved. The whale may be sick or elderly. Some animals might be injured, perhaps from shark attacks or encounters with fishing gear. Some, say scientists, have fatal gunshot wounds, possibly inflicted by fishing crews to deter the animals from taking a chunk of their catch.

Beyond New Zealand's small community of marine scientists who research the animals, these events pass with little attention.

Mass strandings on the other hand, especially over summer like the latest at Golden Bay, frequently hit the headlines with a call to arms for volunteers and images of lifeless black shapes awaiting disposal.

The deadliest months run from December through to March, when as many as 250 stranding episodes are recorded, not just in Golden Bay and not just of pilot whales. So-called stranding "hot-spots" include two beaches on the Chatham Islands, the Coromandel, Northland, Kaipara and Stewart Island. One feature about several of these stranding locations is they have gently sloping beaches and a spit or peninsula enclosing one end.

At Golden Bay, the slope is exceedingly gradual. Ranger Mike Ogle estimates as much as seven kms of damp sandy flats are exposed at low tide.

New Zealand's first recorded stranding occurred in 1840. The largest stranding, of 1,000 whales, was on the Chathams in 1918. On a more cheerful note, when 450 pilot whales came ashore at Kawa Bay on Great Barrier Island in 1985, an astonishing 324 animals were saved.

But despite this cruel natural history of whales and dolphins dying above the tide on New Zealand shores, scientists know little about why the grim death toll persists and what, if anything, could be done to relieve it.

This is not for want of effort.

Strandings occur in oceans around the planet, and immense scientific resource has gone into trying to understand cetacean behaviour and whether it is possible to reduce the toll from animals being caught in shallow waters and unable to make safer depths. But studying animals in the wild is costly and difficult. Unlike some shark species, which have been tagged, released and tracked, no New Zealand pilot whales have been monitored in the same way.

In the absence of a one-size-fits-all explanation, a number of theories behind stranding have arisen, including disease, pollution, climate effects, earthquakes (a popular one this week after Monday's 6.2 Eketahuna quake), seafloor shape and geomagnetic contours to the disorienting effects of naval sonar.

At Farewell Spit, the pilot whales, who live offshore and hunt squid and fish as deep as 500m underwater, can misjudge the slope of the sandbar which seals Golden Bay off from the Tasman. When one gets in trouble other soon follow. The question is why.

Whale expert Dr Rochelle Constantine, a senior lecturer at the University of Auckland's school of biological sciences, says: "We don't know why the whales strand."

She is certain though that the earthquake theory linking seismic shocks to the stranding - which trended this week on Twitter after claims from "moon man" Ken Ring - can be dismissed: "There is no link between strandings and earthquakes."

Scientists understand pilot whales have a social structure which means they are closely bonded to each other as a group. A range of impulses lies behind their bond - the rearing of offspring, mating aggregations, safety in numbers against predators, the returns from hunting as a pack. The bonds can last for years and the ties unite the group, even in strandings.

Samples taken from previous New Zealand strandings shows the whales are genetically similar, though not always closely related. Mothers and calves do not necessarily end up together on the beach, which to Dr Constantine suggests could arise from confusion in the shallow waters.

In mass strandings, it is this group or herd which ends up in trouble. They may follow the lead of a "key animal", effectively the leader of the pack, as it emits sounds the others pick up. But complicating the picture is that not all animals in the herd will become stranded.

Says Dr Constantine: "Sometimes other animals orient their bodies in towards this individual who may, or may not be vocalising more than the others. It's not always possible to tell who the key animal is especially if the stranding occurs along a wide stretch of beach or the sea has washed them around as they come ashore."

This strong group cohesion can be a factor in the sometimes futile results at rescues, as individuals in the herd rejoin their colleagues after people with the best of intentions direct them out to sea. In some strandings, whales may be following the lead of a sick animal, or a female giving birth. In the case of the most recent stranding, autopsies have been done on six whales.

Massey University wildlife pathologist Stuart Hunter said results showed the whales were in good condition and "not starving or emaciated". Further tests would look for parasites and diseases, which wild animals carried. "We'll be looking for any underlying disease. We might not be able to say why they stranded but we should be able to rule out a number of causes."

Some of the samples gathered at Farewell Spit are sent to Auckland University, where Dr Constantine manages the New Zealand Cetacean Tissue Archive. Since 1994, the collection has grown to more than 2000 samples, stored in ethanol in five freezers. DNA from the samples helps scientists keep tabs on population genetics and the state of species in New Zealand waters.

So, could anything be tried to reduce the rate of stranding, along the lines of a warning beacon which could emit sounds the whale could hear and deter the animals from the Farewell Spit trap? Dr Constantine: "The problem is that introducing underwater noise comes with its own problems for other marine organisms. Also we don't know when these strandings are likely to occur so would have issues with knowing when to transmit the noise. We don't know what kinds of noise would act as a deterrent to whales and if used, how long that noise would be effective for. The area that needs to be covered is very large, so the simple logistics of installing and maintaining such devices would be a challenge as well."

After nearly 20 years researching whale behaviour, Dr Constantine believes it is important to realise that "as tragic and as sad as it is (a mass stranding) it is a natural event.

"As far we know pilot whales are not endangered. They have good genetic diversity, they are wide ranging, they travel most likely far out into oceanic waters. That should slightly alter how we think about these strandings. They've been occurring for hundreds and hundreds of years, long before anyone got to New Zealand. And we have every reason to think they will continue to occur."