Deadly Mystery: Why Did 9 Killer Whales Die in New Zealand?

The death count represents 5 percent of the country's total killer whale population.

Why Did 9 Killer Whales Die in New Zealand?

(Photo: Stuff.co.nz)

David Kirby has been a professional journalist for 25 years. His third book, Death at Seaworld, was published in 2012.

Just when you thought things couldn’t get worse for killer whales, nine of them have been found beached and dead on a rocky shoreline at the southernmost tip of New Zealand. The rare occurrence has baffled scientists and left animal lovers mourning the loss, which represents a full 5 percent of the country’s total orca population.

On Monday, a resident discovered the whales washed up in a row along a beach near the town of Tautapere, on the southern end of New Zealand’s South Island, in one of the largest mass strandings of killer whales in recorded history.

The beaching was particularly tragic for Dr. Ingrid Visser, founder of New Zealand’s Orca Research Trust, who has studied the country’s killer whale population most of her adult life and come to know many of its members through diving repeatedly with them. Before the recent mass deaths, the population was estimated at about 200.

Visser, who was on a research vessel in the South Pacific when she received the news and immediately made arrangements to travel to the site, answered some questions via email while en route to investigate. She said strandings of single orcas were not rare, but mass strandings of this magnitude were extremely uncommon.

“The last one in New Zealand was in the 1980s, when 12 animals died,” Visser said. “The largest mass stranding of orcas was in 1955, with 17 animals,” all of whom were euthanized with bullets. This week’s stranding “would be one of the largest where all animals died, that we know of,” she added.

Though she viewed photographs of the dead whales, Visser was unable to determine if it was one of the pods she routinely dives with, photographs, and studies. One orca, a calf, was removed via helicopter by the country’s Department of Conservation, which will perform a necropsy in the hopes of finding clues to what happened.

Like all toothed whales, orcas occasionally beach themselves, though mass strandings are more common among pilot and sperm whales, which live farther out to sea.

The preferred prey of New Zealand killer whales are rays, which tend to gather in shallow bays and inlets. “Orcas strand in New Zealand typically when hunting in shallow water for rays,” Visser said. “I’m not sure if this was the case here or not and won’t know until I get there, if ever.”

Dr. Naomi Rose, another leading orca expert and marine mammal scientist at the Animal Welfare Institute, said in an email: “It isn't all that common for orcas to mass strand like this. It suggests that there may have been an external factor at play, but we'll have to wait for the necropsy results.”

Cetacean stranding remains somewhat of a scientific mystery, and different factors may be involved in different events. “They are like car accidents,” Visser said. “There are lots of different reasons.”

Some whales and dolphins get trapped when they chase prey into tidal waters that recede before they can escape. In other cases, a single ill or injured animal may become stranded, and, being highly social animals, other members of the pod strand themselves as well, to be with their stricken family member.

Another cause of strandings is the disorienting noise created by navy sonar, bombing practice, and war games.

Other possible explanations include bad weather, viral or other parasitic infections, undersea earthquakes, magnetic field anomalies, and unfamiliarity with the local underwater topography.

Visser and other scientists are eager to take samples from the fallen whales. “With my consultation, we removed the only one (the calf) we could get out, in case the weather packs in. This is a really nasty weather area,” Visser said.

“We are coordinating a big team to go down there but need to await Iwi (Maori tribe) permission for anything other than photos and measurements. But they understand our scientific requests, and timing is critical for the samples.”

Like many indigenous people, the Maori believe that orcas are sacred. Now they have lost nine of 200 members of the local population. A tribal spokesman, Dean Whaanga, said members visited the site to give thanks to the fallen animals.

“Like our human friends that have passed on,” he told a local newspaper, “[we give] “a blessing to them and wish them well on their last journey, their final farewell.”

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