Massive numbers of pilot whale strandings recently occurred in Chatham Island in New Zealand.

According to officials, nearly 100 pilot whales died in the mass stranding. The Chatham Islands is a remote New Zealand territory.

Massive beaching

According to New Zealand's DOC or Department of Conservation, most of these strandings or beachings occurred on the weekend; however, rescue efforts have been hampered by the nature of the island's isolated location. Chatham is approximately 800 kilometers (or 500 miles) east of the South Island.

According to Jemma Welch, DOC biodiversity ranger, when wildlife officers arrived at the site, 69 stranded whales were already dead.

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Some whales and dolphins euthanized

She reported that they euthanized an additional 28 pilot whales and three other dolphins. Of the 28 pilot whales, two beached last Monday following the initial whale stranding.

According to Welch, euthanasia was warranted because of the rough conditions at sea and the near-certain presence of great white sharks there, drawn to such beachings.

Welch said Maoris's local community performed a special ceremony to honor the spirits of those stranded whales. The bodies will be left in the area to decompose naturally.

In 1918, there was also a marine mammal stranding recorded in the Chatham Islands. It was the largest recorded stranding in New Zealand, where a thousand individuals beached.

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Pilot whales

Pilot whales are marine mammals or cetaceans which belong to the Globicephala genus. Two species live today: the Globicephala melas or long-finned pilot whale and the G. macrorhynchus or short-finned pilot whale.

These two species cannot be easily distinguished in the waters, requiring skull analysis to tell them apart. 

Pilot whales have a nearly global range. The long-finned pilot whale can usually be found in colder waters, while the short-finned pilot whale is often seen in tropical to sub-tropical zones.

Pilot whales comprise some of the biggest oceanic dolphins; the Orca or killer whale only dwarfs them. These compose the large dolphins in the world and are also called blackfishes.

Long-finned pilot whales usually reach a length of 6.5 meters (around 20 feet). They are the species most commonly found in the waters of New Zealand. Short-finned pilot whales reach only 5.5 meters.

Marine mammal strandings

Scientists have not determined the reasons why mass beachings or strandings of marine mammals occur. They have investigated this phenomenon for many decades, but no definitive answer has so far been forthcoming.

There are several theories of why beachings occur. These include the following:

Illness

Whales or dolphins that strand is sometimes found to be diseased. The pod members may follow their sick leader to the shore and lead to many cetaceans beaching.

Noise pollution

The oceans are made noisy by the presence of humans. The shipping industry and anti-submarine and high-frequency sonars may interfere with the sonar of cetaceans.

The presence of prey or predators

Pods of cetaceans may be stranded as predators pursue them. Conversely, they may also beach as they pursue their prey. 

Extreme weather

Bad weather conditions can disrupt the sonar of marine mammals. Raindrops cause bubbles, which can also scramble their sonar.

Shoreline geography

In some beaches, inclines that are very shallow can cause cetacean sonar to fail to detect obstructions.

These factors can contribute to marine mammal and pilot whale strandings, such as Chatham Island's recent occurrence in New Zealand.

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