They may have gotten knocked around their underwater cave because of an earthquake, but the fish that live in a cavern inside Death Valley National Park are doing better than they have in decades, scientists say.

National Park Service biologists counted 263 Devils Hole pupfish on Thursday, Sept. 29. That’s more than they’ve seen in nearly 20 years, according to an NPS news release.

And that’s right after a 7.6 magnitude earthquake hit Mexico and caused a “desert tsunami” in Devils Hole, sending 4-foot waves sloshing around the deep, water-filled cavern. It’s the only place the Devils Hole pupfish live in the world, meaning they’re some of the rarest fish on earth.

Devils Hole is a limestone cave in Nevada’s portion of the national park that’s partially filled with water and hundreds of feet deep, McClatchy News previously reported. The Devils Hole pupfish live in the upper 80 feet of the water on a “sun-lit shallow shelf at the cavern’s entrance.”

Park officials said the earthquake caused a “seiche,” which is a “wave that swings around a standing body of water,” McClatchy News previously reported. The swells stirred up sediment and rocks from the shallow part of the cave and sloughed off algae growth that the pupfish depend on for foraging and spawning, scientists said in the news release.

U.S. wildlife and park service staff closely watch population levels to manage the critically endangered species, the news release said. Scientists count the fish they can spot on the surface while other scientists scuba dive below 100 feet to count from below, the release said.

While autumn numbers have been increasing over the last nine years from an “all-time low of 35 fish,” the 263 observable pupfish is the highest autumn count recorded since September 2003, according to the release.

Before the 1990s, populations averaged between 400 and 500 in the fall. Numbers have been drastically low during the last two decades, “averaging only 90 fish,” the release says.

And that’s why scientists track the populations long-term, Kevin Wilson said in the release. He’s the aquatic ecologist for Death Valley National Park, and he said the higher population of autumn pupfish could mean important changes are happening in the ecosystem.

Other biologists at the count said the fish appeared to be in “remarkable condition” and were “very active,” the release said.

Jennifer Gumm, who manages the Ash Meadows Fish Conservation Facility nearby for the U.S. Fish and Wildlife Service, said the earthquake may have actually contributed to pupfish spawning, which she called a “fascinating aspect of the behavior of this species.”

The “desert tsunami’” swells sloshed off “algae, invertebrates and other organic matter” from the shelf where the pupfish forage and spawn, the release said.

Michael Schwemm, senior fish biologist for the U.S. Fish and Wildlife Service, called the increasing populations exciting.

“The ongoing trend, especially in this highly variable population, makes clear that habitat conditions have changed in a good way since the lowest counts, and we’re excited about the future directions for research and recovery,” he said.

Biologists will count the pupfish again in spring 2023, the release said.

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