Why do whales beach themselves?

Photo: littlenySTOCK/Shutterstock)

 

Each time a report surfaces of beached whales, we’re left to wonder again: Why do these majestic creatures strand themselves on shore?

It’s not a new question by any stretch. It dates as far back as Aristotle, maybe even earlier.

“It is not known for what reason they run themselves aground on dry land; at all events it is said that they do so at times, and for no obvious reason,” he wrote in “Historia Animalium.”

Artists and historians have captured such events throughout history. We have engravings and paintings of beached whales dating to the 16th century. Today, we have video and photographic evidence of whale strandings from all over the world.

'The Whale Beached between Scheveningen and Katwijk, with Elegant Sightseers' painted by Esaias van de Velde
This Esaias van de Velde painting, ‘The Whale Beached between Scheveningen and Katwijk, with Elegant Sightseers,’ is from 1617. (Photo: Esaias van de Velde/Wikimedia Commons)

Despite the centuries separating the scenes, though, they all show the same thing. A beached whale, or a pod of them, and humans looking on in bewilderment. Sadly, in the thousands of years since Aristotle, we still don’t know much about how to help. We know as much about whale beachings now as Aristotle did in 350 B.C.

“They do so at times, and for no obvious reason.”

We do, however, have a few theories:

Navigational errors

Given that reports of whale strandings date to ancient Greece, it would seem that at least some cases are the result of something going on with the whales themselves.

Bangor University lecturer and cetacean scholar Peter Evans proposes some possibilities in a 2017 article for The Conversation, writing, “Mass strandings of these oceanic species tend to be in very shallow areas with gently sloping, often sandy, seabeds. In those situations, it is no surprise that these animals, which are used to swimming in deep waters, can get into difficulties and even if re-floated will often re-strand.

“The echolocation they use to aid navigation also does not work well in such environments. So it is quite possible that the majority of such strandings are simply due to navigational error, for example when whales have followed a valuable prey resource into unfamiliar and dangerous territory.”

Basically, the whales make a mistake, get lost and can’t get back to deep waters.

Humpback whale swimming along surface of water
Whales use echolocation to navigate, but it doesn’t work well in shallow waters. (Photo: Rainer J. Wagner/Wikimedia Commons)

Solar activity also could be messing with the whales’ navigational ability. A 2017 study published in International Journal of Astrobiology hypothesizes that solar storms, which can alter the Earth’s magnetic field for a short time, disrupt the whale’s migratory patterns and send them into those shallow waters where they get trapped.

Injuries and illnesses

Attacks from other marine creatures and diseases could also play a part in beachings.

Evans briefly mentions that as a whale becomes weaker, it heads for shallower waters so that it can surface more easily for air. If the water is too shallow, it may end up stranded.

“Once their bodies come to rest on a hard surface for any extended period,” Evans writes, “there is a greatly increased chance that their chest walls will be compressed and their internal organs damaged.”

Even without an injury or illness, the animal could simply be too weak to keep itself afloat, thus washing up on shore.

Rescuers assist beached long fin pilot whales at Australia's Hamelin Bay in March 2009
Rescuers assist a beached long fin pilot whale at Australia’s Hamelin Bay in March 2009. (Photo: Tony Ashby/AFP/Getty Images.

In a 2009 interview with Scientific American, Darlene Ketten, a neuroethologist at the Woods Hole Oceanographic Institution in Cape Cod, Massachusetts, mentions pneumonia as a common cause of strandings in the U.S.

Ketten also raises a point regarding whether returning such animals to the ocean is in the animals’ and the ecosystem’s best interest.

“If you have an animal and it is stranded and you insist on returning it to the sea, are you harming the population? If they are sick or diseased, what are we doing to that population pool? I’m not advocating that we don’t rehabilitate animals, if we can. We should understand causes of stranding, but we also have to accept the fact that strandings may be in many cases natural phenomenon.”

Humans can play a role in strandings, too.

The dangers of sonar

A beaked whale surfaces from the water
Beaked whales seem especially sensitive to sonar. (Photo: Andrea Izzotti/Shutterstock)

Sonar is one of the most commonly cited reasons for strandings, specifically for those of beaked whales. Sonar is the process by which vessels emit acoustic signals or pulses into the water to determine the location of objects.

Those acoustic pulses could be harming whales and influencing their navigational abilities.

Evans explains that reports of sonar and whale beachings date to 1996, “after a NATO military exercise off the coast of Greece coincided with the stranding of 12 Cuvier’s beaked whales.” He also cites a May 2000 incident in the Bahamas that involved mid-frequency sonar and more beaked whale strandings. Unlike the ’96 incident, the beached whales in 2000 were examined and signs of hemorrhaging were found around the whales’ inner ear, indicating some kind of acoustic trauma.

A 2003 study published in Nature postulates that sonar induces a kind of decompression sickness, or the bends, in beaked whales. Following a potential sonar-related beaching in September 2002, researchers discovered tissue damage due to gas bubble lesions, an indicator of decompression sickness. How these lesions formed, however, is unknown. One possible theory is connected to the beaked whales’ penchant for deep, deep dives: They hear the sonar, panic and rise to the surface too quickly, causing the lesions.

Changes in the water

A beached whale with netting around its mouth.
Pollution in the ocean, like discarded nets, pose a real risk to whales. (Photo: DejaVuDesigns/Shutterstock)

Humans’ impact on the overall state of the Earth could play a part in whale strandings, too.

Man-made materials in the water, from plastics to fishing nets, can harm whales, leading to injuries that may force them into shallower waters, where they can become beached. The pollution may simply kill them outright, so they wash ashore. Fertilizer and sewer runoffs can create red tides — toxic blooms of microorganisms — which can result in whale deaths and beachings. Such blooms also impact the whales’ food sources, poisoning krill and other shellfish as well.

Warming water temperatures aren’t great, either. Changes in tides due to warming oceans may shift the location of food sources, again forcing whales into unfamiliar territory and possibly shallower waters.

What about mass beachings?

Beachings that involve several whales, sometimes hundreds, are another mystery that scientists just can’t explain. Many of the whales in these strandings are healthy, showing no sign of illness or injury.

One potential explanation is the social nature of whales. Whales travel in pods as a way to survive , with dominant whales leading the group. If the leaders become lost, confused or otherwise unable to properly navigate the waters, it’s possible the whole pod could follow. Additionally, whales may be responding to distress calls from other beached whales. They come to help and end up stranded themselves. Another theory suggests that if a few whales are ill or injured on shore, the rest of the pod may strand itself to be close to the dying members.

After all these centuries, we still don’t know exactly why whales end up on land. It’s a complex and mysterious issue. As complex and mysterious as the creatures themselves.

Source :

MNN

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