Whales May Have Followed Leader to Mass Death
A team of 60 used slings and other equipment to help pull the whales off the sandbanks (Photo by Brodie Weeding/AFP/Getty Images)
The long-finned pilot whale calves, who filled the air with shrill plaintive cries for their mothers at a western Australian harbor, may have been witnessing the adults’ allegiance to a leader in one of the biggest mass strandings of marine mammals.
Too small to get trapped, the calves nudged the rescuers as they swam around them and the 470 beached whales. In September, pilot whales, who are actually dolphins, stranded themselves in three spots at shallow Macquarie Harbor on the remote Tasmanian coast.
As of September 25, a total of 94 whales had been rescued and about 350 had died. Without the buoyancy of the water, the whales were slowly crushed by their own bodies, which can weigh as much as three tons, said Professor Peter Harrison of Southern Cross University’s Whales Research Group.
“Researchers say it’s possible that one leading individual could have mistakenly led the whole group to shore,” said BBC News (September 23).
Following a leader is not always the right move. As it did here, it can end in tragedy.
More than 80 percent of Australia’s whale strandings occur in Tasmania, and many are at Macquerie Heads, which measures 315 square kilometers (195 miles) and has an average depth of 15 meters (49 feet), making it navigable only for shallow-draft vessels. Tasmania’s previous biggest stranding was of 294 pilot whales in 1935. Its last one was in 2009 with 200 pilot whales, according to The Guardian (September 23).
The biggest recorded pilot whale stranding was an estimated 1,000 whales at the Chatham Islands, New Zealand in 1918, according to the New Zealand Department of Conservation.
It is not known, for certain, what caused the latest mass stranding. What is known is that pilot whales, which can grow up to 7 meters (23 feet) are prolific stranders. They are highly socialized, and they communicate with echolocation.
Pilot whales live in female-led, tightly-knit pods of 20 or 30, but they sometimes form temporary “super pods” of up to 1,000, which probably helps them to feed en masse or to avoid inter-breeding, said Dr. Emma Betty, of the Cetacean Ecology Research Group at Massey University, New Zealand.
To communicate, they use echolocation, which is a physiological process for locating distant or invisible objects by sound waves reflected back to the emitter.
“What continues to be the strongest factor is the topography that forms natural whale traps,” said Betty. “The whales are unfamiliar with this topography and also probably how the water rushes in and out with tides.
“They have trouble with the echolocation. Because of the shallow slope, they don’t get a clear picture. They’re failing to detect the proximity of the shore until it’s too late, whereas coastal species don’t have that problem.”
The pod may have come close to shore for food. Once the pod was close, Betty said, members likely became disoriented by the lack of direction.