Massive graveyard in Tasmania: Why do whales beach themselves?

Bad news in Tasmania

The world just woke up to the terrible news: at least 470 pilot whales beached themselves in Tasmania and around 400 are dead. First, a pod of 270 individuals stranded together on Tuesday. They were soon followed by 200 other individuals on Wednesday. This is the biggest stranding event in Tasmania to date. The two pods did not strand in the same area, making the rescue really difficult because teams have to be deployed on two different sites. Rescuing one beached whale is hard enough, so imagine trying to return almost five hundred individuals to the sea. It is impossible. This massive stranding event makes us wonder? Why do whales beach? Why is it often pilot whales?

Credit: Wikimedia commons

Why do whales beach themselves?

Navigation error

Stranding events can happen for multiple reasons. Toothed whales (like the pilot whales currently stranded in Tasmania) use echolocation for orientation. Navigation errors can happen, meaning the whales can enter a shallow bay and not find the exit. This is likely what happened in Tasmania because the coastline is quite shallow. Sometimes, after looking for an exit from a shallow basin for weeks, the whales are too weak to make it out alive, and just beach themselves on the shore, or on a sand bar.

Virus or disease?

Another reason for stranding could be a disease. When whales from a pod are infected by a virus (like the morbillivirus) or toxic algae, they can all become sick and beach themselves. Three pilot whales stranded in the Canary Islands in 2015 died of a morbillivirus infection. Symptoms of morbillivirus include pneumonia, encephalitis, and damage to the immune system, which means the whales cannot float or swim properly and end up beaching on the shore.

Sound pollution

Intense noise can cause whales to beach themselves as well. Pilot whales can dive 800m under the surface to feed on squid. Loud noise can cause short-term responses in the whale’s body. The sound can cause the whales to panic and rush towards the surface to breathe. When the whales try to surface too quickly, it can cause decompression sickness or “the bends” and can cause irreversible damage. In May 1996, 12 Cuvier’s beaked whales stranded in Greece, and 8 of them died. Experts believe a military sonar exercise was responsible for the whales’ death.

Escape from a predator

Finally, to run away from a predator, whales can speed towards the shore and beach themselves. It actually happens in the Faroe Islands. The predator is human and chases the whales with boats towards a shallow bay where hunters wait for the whales to beach themselves and finish the job. You can find out more about whaling here.

We cannot know what happened to the whales in Tasmania until we hear back from the autopsy reports (called necropsies). They will let us know how healthy the whales were if they had the bends, a virus, etc.

Why is it often pilot whales?

Pilot whales are super social. They live in large pods or maternal families. Sometimes, these pods hang out together. When something bad happens like a virus, loud noise, a navigation error, or a predator, pilot whales tend to beach themselves altogether. Scientists still do not fully understand these extreme mass stranding events. When a couple of whales wash up on the shore, it seems like the rest of the group follows. Some stranding events, like the one happening in Tasmania at the moment, can include a couple of hundred whales at a time!

What can we do?

If you are currently in Tasmania, the Department of Primary Industry, Parks, Water, and Environment has advised the public to stay out of the professional team’s way so they can try to coordinate their efforts without too much chaos. They are doing everything they can to rescue the whales that are still alive.

Make sure to read our post on pilot whales. They were our July whale of the month:

The pilot whale – July 2020
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Anaïs is the founder of Whale Scientists. She is a PhD student at McGill University working on killer whale ecology and pollution. You can read more about her here.

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