Whale remains on the ocean floor being eaten by tiger sharks and other scavengers
Laura Gurgas
Computer models help predict the drift of dead whales, allowing authorities to allow their remains to decompose naturally, safely in the ocean.
Dead whales attract large numbers of sharks and are extremely smelly and unsightly when they wash up on crowded beaches, creating logistical problems for local authorities. If ocean currents wash the whales into shipping lanes, they pose a major danger to passing ships.
While most dead cetaceans never wash up on shore, for example, 30 to 40 carcasses wash up on Australian shores each year, a figure that has been growing since commercial whaling was largely abolished in the 1980s.
These carcasses are either left to decompose, buried on shore, taken to a landfill, composted, processed into biodiesel, pulverized with explosives, or carried out to sea where they will drift for days or weeks before sinking.
Sometimes, after being towed away and released, the carcasses wash up again somewhere else, simply shifting the problem.
Computer models can predict where floating debris will end up, but it’s hard to make precise predictions about a dead whale because of its unusual size and shape, he said. Olaf Meineke at Griffith University, Queensland, Australia.
“The most important thing is to know if the whales are returning to shore,” Meineke said.
To learn more, he and his team closely monitored a dead humpback whale that had drifted off the coast of Queensland.
A drifting whale measuring 14 meters in length and weighing an estimated 25 tons was discovered by Coast Guard volunteers on July 16, 2023. The whale was headless, and researchers speculate it may have died in a ship collision.
By the next day, the carcass had swept four kilometers (2.5 miles) away. After locating the carcass, Meineke and his colleagues fitted it with a satellite tracking device.
On July 18, the whale washed up on land. It was then towed 30 kilometers offshore and released again. The team then tracked the whale’s trajectory over 150 kilometers over the next week. Eventually, the carcass either sank or the tracking device failed.
His team found that during the first few days after death, when the carcasses were floating highest, up to 1.5 metres above the water’s surface, wind strength was the biggest factor determining the direction of drift.
“Currents only become important when the carcasses start to decay and become less buoyant,” Meineke says.
After collecting the satellite data, the team used a search-and-rescue computer model to simulate the paths of various objects that resemble the outline of a dead whale, including skiffs, life rafts and small boats called pangas, in the same location and weather conditions.
Meineke said the predicted location was accurate for the first few days, but after six days it was off by 10 to 20 kilometers.
He hopes to repeat the study with more carcasses to evaluate different scenarios and provide more precise estimates of where whale carcasses may wash up.
Moving a dead whale from the beach to a landfill can cost authorities more than 10,000 Australian dollars (about US$7,000) and removes huge amounts of nutrients from the marine food chain, Meineke said.
“The goal is to give local authorities the tools to quickly determine whether it’s possible to tow the whale out to sea and know where it will end up.”
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Source: www.newscientist.com
