It is the fifth incident of this kind to happen in less than a week. Scientists believe the strandings were not linked, and say a variety of factors could have caused them.
Image: picture-alliance/dpa/DEPARTMENT OF CONSERVATION
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Whales continue to die on New Zealand's beaches, as a new mass stranding on the remote Chatham Islands on Thursday killed 51 pilot whales.
Over 90 cetaceans beached themselves on Thursday at Hanson Bay, of which 51 died, the country's Department of Conservation said. Staff found that 40 of the whales had managed to return to the water.
The Chatham Islands had witnessed New Zealand's largest recorded stranding in 1918, which involved 1,000 whales.
Thursday's incident was the fifth of its kind in New Zealand in less than a week. One hundred and forty-five pilot whales were found dead on Stewart Island on Saturday, while nine pygmy killer whales died the following day after being stranded at Ninety Mile Beach on the North Island.
Scientists don't know why whale strandings occur, but they believe they might be linked to a variety of concurrent factors.
According to Dr. Dave Lundquist, a technical adviser on marine species who spoke in a video released by the Conservation Department, whales could be navigating incorrectly or trying to escape predators, or some of them might be sick or injured. He said man-made causes like underwater noise could also contribute.
Lundquist also said there was no evidence to suggest the strandings in New Zealand were linked, despite the cases appearing to be close together both in terms of time and location.
What happens to beached whales?
Every year thousands of whales are found stranded on beaches all over the world. But how do they get there? And what happens once they hit the shore?
Image: picture-alliance/Pacific Press/A. H. Firsawan
A team effort
Earlier this month, locals in Aceh, Indonesia, teamed up to try and help 10 sperm whales that beached themselves in shallow waters. Volunteers managed to pull six of the animals back out to sea, but four died. There is no real consensus on why whales become stranded, but there are plenty of ideas...
Image: picture-alliance/dpa/M. Yani
Follow the leader
Some whale species live in social groups known as 'pods', each of which has a leader the other animals swim behind. If the lead animal finds itself close to the shore and in trouble, it can send out a distress signal. The whales following behind may try to help and end up stranded themselves. There is also the possibility that whales become caught while chasing prey.
Image: picture-alliance/Zumapress/R. Azhari
Manmade strandings
Another school of thought on why whales become beached suggests that overfishing forces the marine mammals to seek food in unfamiliar and potentially shallow waters where they become trapped. There is also some evidence that naval sonar can disrupt and confuse the animals while migrating.
Image: picture-alliance/Zumapress/R. Azhari
Evading the deep
If a whale perishes deep in the murky depths of the sea, its body sinks to the bottom providing nourishment for a plethora of other animals and organisms for years, even decades to come. But those already close to the shore, may wash up on the beach, like this whale that appeared in Rio de Janeiro. If this happens, the animals decompose on the sand - a phenomenon that can cause other problems.
Image: picture-alliance/AA/F. Teixeira
An explosive response
Though these sunbathers appear undeterred, the stench of a putrifying whale carcass would be enough to put many off their holiday. And the smell is not the only issue. When one of these ocean giants dies and begins to decompose, gases build up in its stomach where they are trapped by a thick layer of blubber. If humans climb on, or try to move the dead whale, it can explode.
Image: Getty Images/M. Tama
A sandy grave
Disposing of a whale that has washed ashore can be a difficult task. Because they can pose a risk to public health, leaving them to rot on the beach is not an option. The best way, say some environmentalists, is to bury them on the beach itself, as was the case with the four whales that died in Aceh.
Image: picture-alliance/Pacific Press/A. H. Firsawan
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Karen Stockin, a marine mammal scientist at Massey University, said that while whale strandings are common in New Zealand during the Southern Hemisphere's spring and summer months, such a cluster of incidents in a short period of time is unusual.
She said New Zealand had registered some of the warmest ocean temperatures on record, and she believed this was affecting whale behavior.
"I suspect a lot of that has been driven by the warmer sea surface temperatures that we're seeing at the moment," she said.
Stockin said the higher ocean temperatures were "likely affecting where the prey is moving and as a consequence we're seeing prey moving and [whale] species following."
Dead sperm whale found packed with plastic in Indonesia
