Cold-blooded slaughter
Matthew Denholm and Leigh Dayton

1st December  2004  
©
The Australian

It is not known why they sometimes run aground on the seashore, for it is asserted that this happens rather frequently when the fancy takes them and without any apparent reason.

THIS quizzical explanation of whale strandings was written by Aristotle in 350BC.  Today we still remain baffled by the phenomenon of whales beaching themselves in huge numbers, making mass rotting graves of our beaches and shorelines.  That whale strandings remain one of the world's greatest unsolved mysteries has been demonstrated in three separate beachings of pilot whales hundreds of kilometres apart since Sunday.

On Sunday afternoon, rescuers scrambled to reach a mass stranding of at least 55 pilot whales and 25 bottle-nosed dolphins at a remote beach at Sea Elephant Bay, on King Island, north-west of Tasmania.

On Monday, just as it was confirmed a further 17 pilot whales had also died on King Island, the alarm was raised on the other side of the state.  A further pod of more than 40 pilot whales was reported stranded on the beach at Darlington Bay on the former penal colony of Maria Island, off the southeast coast.  Then 73 pilot whales were found yesterday stranded on a New Zealand beach.

Even Tasmanian whale experts, used to a stranding on average every 12 days on the island state, were reeling.


Many accept the broad theory put forward by Tasmanian zoologist Mark Hindell.  He believes a peak of strandings is occurring as part of a cycle of atmospheric conditions which bring sub-Antarctic waters closer than normal to Tasmania every 10 to 12 years.

These cooler waters are teeming with food, luring whales closer to land than in other years.  In the case of the recent strandings, Hindell believes the pilot whales were too close to land when seeking the abundant squid.  It only takes one whale to beach for an entire pod to respond to its distress signal and also become stranded.

Hindell's findings help provide a backdrop to explain the larger number of strandings in some years, but do not answer the question of how whales become beached.  Yesterday, fingers of blame for the three strandings in 48 hours were also being pointed at oil company exploration in Bass Strait, taking place as late as Friday.

Conservation groups and the Australian Greens called for the exploration to be suspended until after the whale migration season, pointing to evidence that dynamite charges used to generate seismic "sound-bombing" of the ocean floor can disrupt whale and dolphin sonar -- which they use to navigate.  Government-paid researchers are careful about discussing this theory in public but believe it should be further investigated.

"It's important to have an open mind," says Rosemary Gales, who has spent 20 years researching whale strandings.

A senior marine biologist at Tasmania's Nature Conservation Branch, Gales was among those who rushed to King Island on Sunday afternoon, only to realise the alarm had been raised too late to save those whales stranded.  On Monday, she was sent scrambling to Maria Island on the other side of the state.  While 23 whales were successfully returned to the water and appear to have safely found open sea, Gales now has the grisly task of conducting autopsies on the 19 whales that died.

As usual in these cases, sections of the inner ear from some of the dead whales will be examined for the presence of infections that can cause strandings by disrupting the whales' sonar.  Locals on King Island reported seeing shark bites in some of the dead whales on Sunday, suggesting they may have been corralled into danger and shallow water by sharks.  This was also suspected at Maria, but a fly-over of the area by the National Parks and Wildlife Service failed to spot sharks.  And several experts have discounted it as a cause in either of the Tasmanian strandings.

Sometimes the seabed contour can impair whale navigation because their sonar signals are disrupted, but experts say this is unlikely to have been a factor in either of this week's Tasmanian strandings because of the nature of the beach landscape.

Instead, a far more intriguing and potentially sinister line of inquiry has emerged from the latest strandings -- cold-blooded murder of long-finned pilot whales by bottle-nosed dolphins.  At Maria Island, a pod of about 50 of the dolphins could be seen just metres offshore.  Experts are puzzled that the dolphins would not leave and were behaving aggressively, despite none of their own number being stranded.

"Locals on King Island were adamant they observed similar behaviour in the dolphins," Gales says.  "Locals and police trying to deter the animals from stranding observed the dolphins herding the whales ashore and stopping them from going to the open sea."

Another whale stranding expert with 20 years' experience in Tasmania, David Pemberton, believes the dolphins are capable of corralling whales into danger and death.  "I believe they could -- yesterday at Maria they were behaving very bolshie and aggressive and we are for the first time looking at whether the dolphins are part of the problem or whether they are just hanging around," he says.  "We will now be looking very closely through the data to understand the relationship between the dolphins and the pilot whales in past strandings."

Gales and other researchers will also take skin samples for DNA profiling to examine whether the three pods of pilot whales stranded in recent days are related.  "Skin genetics will tell us if they are related to other stranded whales and allow us to look at the relatedness between the King Island, Maria Island and New Zealand strandings," she says.

"We are just looking at DNA profiling and over time we will be able to build up a genetic picture of whales that are stranded in Tasmania and compare those with samples from overseas."

As to the wider search for answers, researchers such as Peter Gill, a doctoral student at Deakin University in Geelong, say the effort is complicated by each event having unique factors.  "It's a case by case thing," says Gill.

While the zonal westerly winds theory posed by Hindell's group may be part of the answer to the present cycle of strandings, a host of other explanations have been suggested by teams elsewhere.  Gill ticks them off, beginning with "geomagnetic anomalies" -- the natural but abrupt change of the Earth's magnetic field -- along a coastline that could confuse migrating animals.  As well, he says researchers have linked noise produced by humans to the problem.  For example, military tests of an acoustic system for detecting submarines was implicated in a series of mass strandings of Cuvier's beaked whale between 1991 to 1997 in the East Ionian Sea.

And just three years ago, US Navy experts concluded that strandings of beaked whales in the Bahamas in 2000 were caused by an unusual combination of factors including nearby military exercises, sea-bottom contour and water conditions that may have channelled and magnified the navy's sonar pings.

Some of the stranded animals even had bleeding ears, probably produced by the mighty pinging sounds.  According to Gill, some researchers suggest that on occasion whales may strand due to a type of decompression sickness -- a whale version of the bends suffered by human divers -- triggered by exposure to sonar.

Thousands of years since Aristotle's observation, we may be starting to ask the right questions, if not yet finding the answers, to an age-old mystery.

Leigh Dayton is The Australian's science writer.  

Matthew Denholm is The Australian's Tasmanian correspondent.


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