Updated 26 March 2013

Why whales beach themselves

Science remains perplexed about the phenomenon of mass whale strandings.

Mass suicide? Submarine noise pollution? What makes whales head inland from the safety of the deep and should we try to stop them?

We’ve become used to blaming humans for scenes of environmental carnage and loss, of which whale beachings, such as those at Long Beach in Cape Town on Sunday and at Kommetjie in 2009 seem a particularly poignant example. But it’s not always (all) our fault.

A centuries-old mystery
The historical record shows that whales have been beaching, or “stranding” as marine biologists prefer to call it, on shores around the world for hundreds of years, long before motorised shipping and human-induced climate change.

So, unlike when an oil spill coats penguins, whale stranding is not peculiar to our age of rapid environmental degradation. And as much as we'd like to be able to rage against some clearly-defined environmental criminal for a beach strewn with dead whales, or to have scientific findings show that these intelligent creatures are so traumatised by the state of the oceans that they suffer major depression and lose the will to live, the real cause is more likely to be multifactoral and obscure.

Potential causes
Single whale strandings - when one animal, or a mother and calf, become beached - are relatively straightforward to explain: an old, sick or injured whale's strength and navigation abilities failed, causing it to wander too close to shore. There is an obvious human factor in some of these cases, for example where a whale has collided with a vessel or become entangled in fishing gear.

Mass strandings, defined as the beaching of two or more (sometimes up to a couple of hundred) whales, are much more perplexing. Multiple-species strandings, where different marine animals are affected, also occur. Here are some of the theories scientists have put forward:

Following a compromised leader
Whale species that live and travel in pods may follow a leader whale who has become ill or disorientated, or who has made some error of judgement, into dangerously shallow waters. Whales also tend to converge around a member of a pod who sends out distress calls.

Following the food source shorewards
Changing weather and climate patterns may also nudge food sources - colder, nutrient-rich currents - away from the open ocean and closer to shore, where whales and other animals will follow them. There is speculation that climate change may be responsible, for example, for the high number of whales beached (over 500) along the Australian coast this year.

Navigation failures
The means whales use to find their way over often vast distances are not well understood, but it is possible that these systems sometimes fail them in negotiating the topography of coastline and ocean floor. One theory, for example, is that whales' echolocation abilities don't sense gently sloping coastal floors, and sometimes they come in too close to shore, not realising how shallow the water has become.

Submarine human noise
Most interesting and controversial of the proposed theories is that whale stranding may be a result of human-generated noise pollution.

Noise from ships' engines and sonar are thought to interfere with whales' ability to communicate and feed, and may compromise their navigational abilities too. Some levels of sonar may even cause damage to the whale ear and brain, or other tissues. Gas bubbles and haemorrhaging in the tissues of whales stranded shortly after naval exercises may indicate that whales suffer a form of "the bends", similar to human divers. The sonar may startle the animals into surfacing too quickly, or it may directly cause expansion of gas in the blood.

A whale out of water
Whales get into trouble quickly when out of their natural depth. The adaptations that make them so majestically suited to their marine environment are what renders them so vulnerable on dry land: their insulating layer of blubber, superbly effective in keeping out the sea's cold, causes rapid overheating. Their huge size, easily supported in the water, crushes their lungs and compresses and kills muscle cells, releasing toxins that cause kidney failure.

These changes are rapid and soon irreversible. One should keep in mind that a stranded whale might be weak and dehydrated, maybe already dying, even before it washes up on shore.

Should we try to save them?
The impulse to save the life of a fellow-creature, especially a member of a highly intelligent mammal species, is commendable. But we have to accept that it may sometimes be misguided, and even result in further suffering.

Veterans of wildlife rescue and rehabilitation know that the stress of the rescue effort itself may prove fatal to an animal, and should only be attempted if there is a reasonable chance of success. Wildlife rescuers are also only too familiar with the concept, and necessarily common implementation, of euthanasia.

Not only is euthanasia a possibility under these circumstances, it’s part of formal wildlife rescue protocol in many countries. For example, in March this year, it became policy in the United Kingdom that stranded deep-sea whales be euthanased without delay by lethal opiate injection, unless they can be moved very quickly back to the deep ocean – which is usually not possible in the UK.

Dr Peter Best, cetacean expert at the South African Museum, Cape Town, has the following to say about the success rates of rescued whales:

"To accurately measure sucess rate one would have to put a satellite tag on one or more animals to follow their fate once refloated - just disappearing is not necessarily proof of survival; they could (as has happened previously) restrand elsewhere shortly afterwards.

"Pushing animals out one by one usually has limited success because social factors (presumably) propel them to come straight back. Better success may be achieved by moving animals in batches and holding them offshore or in a pen in a different location before releasing en masse. This however can be a mammoth undertaking, especially with animals the size of false killer whales, and may be completely unfeasible if vehicles/machinery cannot be brought onto the beach.

"Rehabilitation in captivity is an option for a few individuals, but not in our case because we have no such facility in Cape Town. Leaving them to die is the last option, favoured by some, but others prefer (as in the Kommetjie case) to shorten their suffering through euthanasia."

The true tragedy
Whereas in 1809 a beached whale wasn’t too sad an occurrence because the oceans were still teeming with them, in 2013 it is far more of an emotionally-charged issue, in part because we know we have so decimated the numbers of these extraordinary beasts that we can't afford to lose more.

Whether the deaths of stranded whales comprise an environmental “tragedy”, as it is often named by media and public, is debatable. The real tragedy is the ongoing, slow death of the planet’s oceans. Whales, more than any other animal, have become icons of that struggle to survive - which we know but don't truly believe or grieve about until we see it happening, on a sunny beach right before our eyes.

Information sources:
Bradshaw, et al. Mass Cetacean Strandings - a plea for empiricism. Conservation Biology, Vol.20 (2) April 2006.
Jepson, etal. Gas-bubble lesions in stranded cetaceans Nature, 425, October 2003
Jha, A. Beached whales to be put down to avoid further suffering. Guardian online. 24 March 2009.


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