In November 2016, a magnitude 7.8 earthquake rocked the southern island of New Zealand, causing aftershocks for the following three days. Meanwhile, two researchers from Otago University were stranded in a rental house in Kaikoura, where they had been studying sperm whales in the undersea canyon.

Kaikoura was near the center of the earthquake, which stretched from Christchurch to Wellington on the north island’s southern tip. The researchers couldn’t get back on the water for a few days, but they used the opportunity to observe the effects of the earthquake on sperm whale behavior. Their results, published last month in the journal Deep Sea Research Part I: Oceanographic Research Papers, show that the earthquake altered the whales’ eating behavior for a year.

“We just happened to be at the right place at the right time,” University of Otago marine scientist and study co-author Will Rayment tells Joshua Rapp Learn at National Geographic. “You can’t plan for something like this.”

When the earthquake initially hit, one of the researchers in Kaikoura and co-author of the latest study Liz Slooten told New Zealand’s 1 News that the whales likely swam far away quickly. Earthquakes are some of the loudest possible noises underwater, comparable to explosions. Slooten said that sperm whales in particular “are known for not appreciating loud noises,” so much so that they sometimes swim to the surface so quickly that they give themselves decompression sickness, which is sometimes called "the bends." It took six days until the researchers spotted their first whale after the earthquake.

In the immediate aftermath of the quake, New Zealand Radio’s Alison Ballance reported that, as a rough guide, the bigger an animal’s size, the better it fared. That was good news for large, charismatic animals like whales and dolphins, but bad news for the mud-dwelling marine invertebrates that the ocean food chain relies on.

A study in 2018 by New Zealand’s National Institute of Water and Atmospheric Research (NIWA) found that the earthquake had flushed over 900 million tons of mud and sediment—and all the invertebrates that lived in it—out of the underwater canyon and into the deep ocean.

"The event has completely changed much of the canyon floor, eroding into rock and moving dunes of gravel through the lower canyon," NIWA marine geologist Dr Joshu Mountjoy told the New Zealand Herald’s Jamie Morton at the time.

Squid prey on the invertebrates, and sperm whales prey on squid; so when the canyon was flushed out by the earthquake, the whales had to change their eating habits, which is what the whale researchers in Kaikoura observed.

The team of researchers observed that the whales moved to hunting grounds in deeper parts of the canyon, and took longer breaks when they resurfaced, compared to their pre-earthquake habits. The whales spent 25 percent longer at the surface between dives, which could mean that they’re gathering more oxygen and preparing their muscles for a deeper dive, Slooten tells National Geographic.

The research could be useful for government agencies that enact fishing quotas, University of Aukland marine mammal ecologist Rochelle Constantine, who wasn’t involved in the study, tells National Geographic.

Juvenile invertebrates began to reappear in the head of the canyon, a sign of ecosystem recovery, about ten months after the quake, NIWA found. Then, about a year after the quake, the whales returned to their normal location and patterns of feeding and surfacing.

“It gives you an idea of how resilient these deep-sea communities are,” Rayment tells National Geographic.