Nearly 500 pilot whales have died after beaching on New Zealand’s remote Chatham Islands in two mass strandings over the weekend.
As many as 250 pilot whales were found beached at Chatham Island, 840 kilometers east of the main South Island, on Friday, and three days later (10 October) another 240 whales came ashore on Pitt Island/Rangiauria, reports AFP.
The stranded whales had to be euthanised as the Chatham Islands is far from the New Zealand mainland which makes it ‘alomst impossible’ for rescue teams to reach in short notice, reports CNN.
Moreover, shark-infested waters make it dangerous to actively refloat stranded whales on the islands, as per The Guardian.
“Due to the risk of shark attack to both humans and the whales, the surviving whales were euthanised by our trained team to prevent further suffering,” Dave Lundquist, a government technical marine advisor, told AFP.
Daren Grover, general manager of rescue organization Project Jonah, said many of the whales were already dead when they came ashore and the rest were ill, as per CNN.
The Chatham Islands are “a stranding hotspot, among the top three places for strandings in New Zealand”, says the Department of Conservation, as per The Guardian.
Mass strandings are common on the Chatham Islands with the largest beaching recorded there in 1918 involving an estimated 1,000 whales.
What are mass strandings and what can be the reasons behind them? Let’s decode the topic.
Mass strandings
When marine animals such as whales and dolphins wash ashore, the phenomenon is described as beaching or stranding.
There are many cases when a group of these animals beaches themselves together which is called mass strandings.
When marine animals wash ashore, the phenomenon is described as beaching or stranding. AFP File Photo
As per The Conversation, the most frequent mass strandings are visible in pilot whales. The other species that usually beach themselves include false killer whales, melon-headed whales, Cuvier’s beaked whales and sperm whales.
“All of these normally live in waters over 1,000 metres deep and are very social, forming cohesive groups that in some cases may number hundreds of animals,” Peter Evans, a senior lecturer at UK’s Bangor University, writes for The Conversation.
Causes for mass strandings
The mass strandings have increased globally, notes Scott Elias from the Institute of Arctic and Alpine Research, University of Colorado, in his book Threats to the Arctic.
Even as scientists are yet to find out the reasons behind mass strandings, some believe that pods divert from their tracks after feeding too close to shore, reports AFP.
Many mass strandings occur in very ‘shallow areas with gently sloping, often sandy, seabeds’, as per The Conversation. Hence, these marine animals are unable to use their echolocation ability that is designed for deep water.
Water can recede during a tide cycle and then if animals navigate into shallower water, it could cause trouble for them, Grover tells National Geographic.
Natural causes can also be behind mass strandings. Sick or injured whales may seek shallower waters to come up to the surface to breathe easily.
In September this year, as many as 14 dead sperm whales washed up on a beach at King Island in Tasmania, Australia. AP
Moreover, some healthy whales might also follow the diseased ones to the shore due to their strong bonds. If the healthy individuals are tried to ‘refloat’ in the ocean, they are likely to come back to the shore if they hear a distressed pod’s call, as per National Geographic.
Man-made reasons
Human activities may also be a reason for beaching.
Fishing, pollution, and ship strikes can injure marine animals which can lead to strandings.
Getting caught in fishing lines is the primary human-made cause of death for cetaceans, notes National Geographic.
“Noise pollution, including sound pulses from the use of sonar and seismic surveys, interferes with whales’ ability to communicate and navigate and can drive them ashore by deafening, disorienting, or frightening them,” reports National Geographic.
In May 2000, a beaked whale mass stranding was reported in the Bahamas that coincided with a naval activity using loud mid-frequency sonar, as per The Conversation.
During the examination, haemorrhaging, mostly around the inner ear was found in some of these dead whales.
Kevin Robinson, director of the Cetacean Research & Rescue Unit, a Scottish marine conservation charity, told National Geographic that sonar can injure the ears of the whales as sound travels faster through water than air and its intensity is longer.
The injured and weakened whale will eventually drift to the shore with the current.
Some recent mass strandings
On 20 September this year, as many as 200 stranded pilot whales died on the west coast of Tasmania, Australia. The state authorities managed to refloat 44 animals.
A day before, 14 sperm whales that beached died on King Island, located in the Bass Strait between Melbourne and Tasmania’s northern coast.
As per official data, around 300 animals are beached annually in New Zealand, reports AFP.
Nearly 470 pilot whales washed ashore in Australia in 2020, the nation’s worst recorded stranding. After a week-long effort, 111 of the animals were rescued while 350 of them died.
At Farewell Spit, Golden Bay on the South Island of New Zealand, an estimated 600 to 700 whales were stranded in 2017.
Around 300 sei whales were stranded in southern Chile’s Patagonia region that year.
With inputs from agencies
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