Australians watched in horror last week as 230 pilot whales stranded on a beach near Macquarie Harbor on Tasmania’s west coast. A few whales were rescued, but the vast majority died. This left a big problem: what to do with all the decomposing whale carcasses?
Authorities decided to drag the dead animals out to sea, hoping they would eventually sink to the seabed.
Such mass strandings of whales are sad to see. But in this case, the aftermath offers a fascinating opportunity for scientific discovery.
As the dead whales decompose, an amazing and rare chain of events is likely to flow through the marine ecosystem – ultimately leading to an explosion of activity and new life.
A 600 ton problem
Massive strandings of whales happen fairly regularly – especially in Tasmania – but no one really knows why.
Days before this latest incident, 14 sperm whales stranded off King Island, northwest of Tasmania.
And in 2020, around 470 pilot whales were stranded in Macquarie Harbour. While many were pulled out to sea, some of these carcasses washed up and rotted on the beach – an entirely natural process.
However, pilot whales are large animals. Males weigh up to 2,300 kg, which means they take a long time to decompose. The stench of two tons of rotting whale blubber soon becomes unbearable, and carcasses are often buried.
This time the authorities decided to drag the dead animals out to sea. The ABC reported that it took local salmon farm workers nearly 11 hours to dispose of 204 dead whales weighing between 500 and 600 tons.
They were tied to a 400-meter rope and towed by boats 40 kilometers before being thrown into the deep waters of the Indian Ocean.
Some carcasses may wash back onto shore, but most are likely to be scattered with the tides and currents.
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Shark Bait? Probably not
The big question is: what happens to all that whale mass that gets thrown into the sea?
Initially, a dead whale tends to float to the surface as it begins to decompose and its intestines expand with gas. While this is happening, marine scavengers like sharks and seabirds are likely to feast on the remains.
Some people may be concerned that whale carcasses attract sharks that could pose a threat to humans.
Admittedly, encounters between sharks and humans are increasing in Australia and elsewhere. But they are still very rare.
A 2012 report to the Western Australian Government found whale carcasses to be a risk factor associated with shark attacks and said caution should be used around a dead whale in the water.
However, the same report found that of 26 shark attacks examined, most took place more than a kilometer offshore. While there’s no doubt that sharks are attracted to dead whales, the data isn’t clear on whether a whale carcass directly translates into an increase in shark attacks on humans.
Research has shown that whale carcasses are less likely to wash up on shore where shark feeding can be observed. So as long as the carcass is kept far from shore and people keep their distance, the threat to humans from shark encounters seems extremely small.
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From death comes new life
Inevitably, the whale carcass will begin to sink. Most ocean life is found relatively close to the sea surface, so when the water is relatively shallow, much of the carcass remains are quickly eaten by scavengers once it reaches the sea floor.
But these carcasses were disposed of in deep water. The deep sea can be a barren place where abundant food sources are scarce. So the appearance of a single whale carcass can charge an entire ecosystem.
In no time, new life and activity can erupt around the dead animal. This process is known as “whale fall” and has been studied by scientists, sometimes using remote-controlled vehicles. On the sea floor of the North Pacific, whale fall has been found to support the survival of at least 12,490 organisms from 43 species.
Deep sea sharks will make the most of the carcass. A variety of other animals including hagfish, squid, crab, lobster, worms and sea cucumbers will also join in. Meanwhile, bacteria work unobtrusively in the background.
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According to the British Natural History Museum, a single whale can provide food for animals during the scavenging phase for up to two years.
Other animals and bacteria survive on the chemicals derived from the rotting carcass.
These organisms, known as “chemotrophs,” were thought to be found only in underwater volcanic vents, where they use hydrogen sulfide as their primary energy source. Research has shown that a similar group of animals will recruit around dead and decaying whales, creating a completely self-contained ecosystem based on a gas that smells like rotten eggs.
Few organisms can break down the remaining bones, which can take up to ten years.
So take a moment to look at the impact of 204 whale falls in a small stretch of ocean off Tasmania. Right now they are probably creating interconnected sea metropolises of a kind rarely seen.