Fish out of water

In an isolated, small cavern filled with geothermal water in the Ash Meadows National Wildlife Refuge in Southern Nevada, there’s a tiny desert fish that lives no where else. And there’s only about 35 of them left.

This pool—Devils Hole—is only connected to other waterways in the subterranean, so these fish cannot swim to another location. University of Nevada, Reno hydrological sciences professor Scott Tyler is the principal investigator on Las Vegas Desert Research Institute hydrologist Mark Hausner’s new study that details how climate change is bringing this fish—the Devils Hole pupfish—to the brink of extinction. The study was completed for Hausner’s dissertation as a student at UNR.

“The fish live in this sort of strange world, and they like to spawn when there’s food available, and that happens when the sun gets high enough in the sky in the springtime to hit the water surface in Devils Hole,” Tyler said.

The sun allows plankton, diatoms and other food sources for the pupfish to grow in the water, but it’s also when the water temperature is at its highest.

“So the period when they can actually spawn or lay their eggs and hatch is a somewhat narrow window,” Tyler said. “So what’s happening is that as the climate changes, the air is warming so the pond surface is getting warmer faster in the season, so before the sun comes up to make the food, the water is already getting too warm for them to spawn effectively.”

They measured water temperature, modeled how the water mixes and overturns seasonally in Devils Hole and took the Intergovernmental Panel on Climate Change’s predictions for climate change and ran them together in a numerical model to determine what the effects will likely be on the pupfish. They found that the optimal recruitment period—the time when conditions are ideal for hatching and feeding of the larvae—will be shortened by two weeks by mid-century. This is in addition to the one week the period has already been shortened because of warming that has already occurred.

The water level in Devils Hole also contributes to warming—it’s about a foot lower than it has historically been, which makes the water easier to heat. Tyler said this is partly because of drought conditions and climate change, but it also has to do with groundwater pumping for agriculture in the late ’60s. This was halted by the Supreme Court, but it still occurs in the area—just farther away.

There are many questions about this fish species and Tyler sees these as opportunities to learn more and then apply it to other species and topics. Where did these fish come from? How did they get to Devils Hole? And how did they survive around 10,000 years of isolation and breeding with very limited genetic material? Part of the reason these fish are important is for scientific study, but Tyler also says that all species are important.

Projects to save this species from extinction are underway and varied. Some eggs have hatched and survived outside of Devils Hole in an aquarium and scientists are working to get them to breed outside, too. Hausner is also using models to look into ways to cool the water—maybe by shading the hole—and ways to raise the water level in order to counteract the warming.

Tyler said this project could open doors to new research in the future.

“We’ve combined strong engineering and mathematics with ecology, and bringing those two disciplines together is pretty powerful,” Tyler said. “It kind of lays out a little bit of a pathway to look at other species that may be impacted by climate change.”