Turquoise Threads Among the Gold

It’s late March in Death Valley, the spring of the Big Bloom. Thousands have come here to see the best wildflower show in years—acres of desert gold, phacelias, gravel ghost, desert five spot. Others are kayaking the ghost of Pleistocene Lake Manly in the Badwater Basin. And here I am, looking at fish.

In a barren valley between Stovepipe Wells and Furnace Creek, the shallows of Salt Creek are alive with pupfish: Salt Creek pupfish (Cyprinodon salinus salinus), to be exact. It’s spawning season and the males, hanging out at the edge, are wearing their brightest colors. To quote ichthyologist Robert R. Miller’s 1943 description of the species: “In breeding males the sides are bluish to turquoise, with bronze reflection, and deep, purplish-blue iridescence appears along the back and upper sides& The broad cross-bars are deep bluish-gray.” The females, in subtler brown, congregate in midstream.

This is a pupfish lek—a group display by courting males, similar to the behavior of prairie chickens, birds of paradise, and hammerhead bats. Every couple of minutes a brown female approaches a turquoise-purple male. Sometimes he chases her away; male pupfish prefer larger, more fecund females. But here’s a pair swimming side by side in parallel S-curves, quivering as sperm meets egg. Then she heads back to midstream, and he remains to guard his display territory—and, incidentally, the egg now glued to the substrate.

It’s a boom-and-bust world for the pupfish. With a generation time of two to three months, population can increase rapidly; Miller estimated highs in the millions. But they can be trapped in side pools or washed out of the streambed entirely by flash floods, providing a bonanza for ravens and other scavengers. A Panamint Indian named Tom Wilson told Miller his ancestors used to scoop the pupfish up in baskets, then bake them with alternating layers of fish, tules, and hot ashes.

Salt Creek is not what you’d consider prime fish habitat. There’s water year-round, but it shrinks to a few pools in midsummer. The water temperature varies from near freezing to over 104 F. It’s nearly as salty as the sea and laced with boron (39 parts per million). But Salt Creek is a piscine paradise, compared with nearby Cottonball Marsh, where the closely related C. s. milleri lives. (The “cottonballs” are nodules of borate.) In summer the pools in the marsh can be less than 4 inches deep and the salinity can reach 4.5 times that of the ocean.

But pupfish thrive in such places. Some twenty species are scattered through the desert Southwest and northern Mexico, isolated from each other in islands of water in a sea of sand. They’re in California’s Owens Valley, springfed creeks in west Texas, New Mexico’s Tularosa Valley, the Bolson de Cuatro Cienegas in the Mexican state of Coahuila. Not far from Death Valley, two pupfish species survive in Nevada’s Ash Meadows. One, the Devil’s Hole pupfish (C. diabolis), has the smallest habitat of any vertebrate animal: a limestone shelf about 20 meters square in a subterranean pool. Litigation over Ash Meadows’ groundwater and the fate of C. diabolis made it all the way to the Supreme Court in 1976. The fish won.

You’d be tempted to think of these extremophiles as the product of millions of years of evolutionary fine-tuning that finally have enabled them to live in such inhospitable environments. Not so. Those environments are fairly young, for one thing; the Mojave Desert dates only to the end of the last glaciation, about 12,000 years ago. And the pupfish species are also young. Given the chance, they’ll interbreed freely with each other, and there’s little genetic variation between species. (There’s almost no variation among Salt Creek pupfish, suggesting a recent genetic bottleneck when the species was reduced to a handful of individuals.) Miller speculated C. salinus is about as old as the Mojave, with the split between the Salt Creek and Cottonball Marsh forms occurring about 2,000 years ago.

It’s true that pupfish in places like Salt Creek can tolerate a range of temperatures, salinities, and high mineral and low oxygen content that would kill most other fish. But so can pupfish that live in freshwater springs at a constant year-round temperature. Those tolerances seem to be not specific adaptations to present environments, but a legacy from a common ancestor that must have been one tough little fish.

The progenitor of all the desert pupfish species is thought to have inhabited ancient estuaries prone to sudden shifts in salt content. It followed the Colorado River up a marshy delta that reached all the way to the Grand Canyon, then through a chain of drainages into Lake Manly and the other Pleistocene lakes of the Basin and Range province. The lakes teemed with fish, but when they shrank away, only the pupfish could handle the harsh new world.

Unlike some of its kindred, the Salt Creek pupfish isn’t considered endangered. Yet. Hydrologists recently traced the source of Salt Creek to groundwater around Furnace Creek, which also supplies a resort complex and an 18-hole golf course. You think fish in the desert are anomalous? Try golf.

Joe Eaton writes about wildlife for the Berkeley Daily Planet, the San Francisco Chronicle, and others.

Comments are closed.