Earthquakes can make it harder for whales to find food, first-ever study says

In 2016, a major earthquake wiped out whole animal communities, sending impacts reverberating up the food chain.Monday, 3 February 2020

Earthquakes can disrupt sperm whales’ ability to hunt for up to a year, according to the first-ever study to look at the effects of the geological events on marine mammals.

On November 14, 2016, the magnitude 7.8 Kaikoura earthquake struck New Zealand’s South Island, causing a destructive tsunami, as well as two deaths and a few dozen injuries. Under the surface, the seismic event spawned strong currents that swept away and mostly killed off diverse ecosystems of invertebrates living along the Kaikoura underwater canyon. The massive landslide not only clouded the water, it flushed the animals hundreds of miles away, likely rearranging the makeup of the entire ecosystem.

As a result, sperm whales had to dive deeper and longer to find food—a “major shift” in their behaviour, says co-author Liz Slooten, a marine biologist at the University of Otago in New Zealand.

Slooten was studying sperm whales in the Kaikoura area with Ph.D. student and lead author Marta Guerra when the earthquake occurred. The scientists recognised it as a rare opportunity to research how a large-scale natural disaster can impact sperm whales, which are considered vulnerable to extinction by the International Union for Conservation of Nature.

“We just happened to be at the right place at the right time,” adds study co-author Will Rayment, a senior lecturer in marine sciences at the University of Otago. “You can’t plan for something like this.”

The impact earthquakes have on land animals has been well documented, but scientists know relatively little about what happens underwater. Recent research on Caribbean sharks, for instance, has revealed the fish dive deep to escape roiling surface waters during hurricanes.

Such research is important for government agencies, which may need to take recent earthquakes into consideration when considering fishing quotas, notes Rochelle Constantine, a marine mammal ecologist at the University of Auckland who was not involved in the study.

Diving in

The Kaikoura underwater canyon, part of a mountainous coastal region, drops to up to half a mile deep not far from land. “There’s only a couple of other places in the world where you can see sperm whales so close to shore,” says Slooten, whose study was published recently in Deep Sea Research Part I: Oceanographic Research Papers.

The canyon’s upper reaches are rich in invertebrate life, providing food for the squid and bottom-dwelling fish that make up the sperm whales’ diet.

So when the flushing event scoured out these smaller life-forms, it had “had severe consequences for the community around there,” Rayment says. “That effect flowed all the way through the food chain.” (See 14 jaw-dropping photographs of whales.)

As part of their ongoing study, the scientists were tracking 42 individual whales, which they'd identified by their unique tail flukes. After the earthquake, the team used directional hydrophones to tune into the cetaceans' sounds, and then traveled to the source in their boat.

Once close to the whales, the scientists would time when the animals came up for air and rested between their dives. In all they recorded data on 40 whales, showing that the abundance of whales in the general area did not change post-quake. However, the whales altered how they used their habitat.

The results revealed sperm whales spent about 25 percent more time at the surface between foraging dives than they had before the quake. Slooten says this suggests the whales were gathering more oxygen and recharging their muscles for longer or deeper dives—likely because less prey was available.

Supporting this theory, before the quake, the whales often concentrated their foraging in the upper part of the canyon. But afterward, the whales mostly abandoned that area and ventured into deeper parts of the canyon. (Read how earthquakes happen in more places than you might think.)

“Now they’ve got a much bigger range, and clearly are moving in much different ways to find prey,” Constantine says, adding that this area is a key feeding area for adolescent male sperm whales.

Bouncing back

A year after the earthquake, the researchers observed the whales returning to their past surface-breathing intervals—perhaps because sediment settled and the invertebrate community began to recover. (Learn about Caribbean sperm whales’ distinct culture.)

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

But he and his colleagues will continue long-term monitoring to see if there are effects they missed. Sperm whale activity in the area had already been declining, though it’s unknown whether it’s due to natural changes in prey abundance, whale-watching tourism, fishing, or warming ocean temperatures.

“There is something going on in Kaikoura,” she says.

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