The Impoible Fish: Devils Hole Pupfish Puzzles Scientists

The confusing, mysterious and unapostrophed Devils Hole pupfish | Photo: Olin Feuerbacher, USFWS

The Devils Hole pupfish (Cyprinodon diabolis) is an evolutionary locked-room mystery. It shouldn't be where it is, and we don't know how it got there or how it survives.

Until recently, it had seemed certain that the pupfish had inhabited the water-filled cave called Devils Hole for a long time, maybe thousands of years. Genetic research, though, suggests that the species is only a few centuries old. Other studies question how much longer it can persist as the extreme conditions in the cave become worse.

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Most visitors to Death Valley National Park, coming for the wildflowers or the geology, don't make it to Devils Hole. It's across the state line in Nevada, a disjunct bit given Park status following a landmark US Supreme Court decision that kept the cave from being pumped dry. The Devils Hole pupfish exists nowhere else in the world. With perhaps the smallest habitat of any known vertebrate, the inch-long fish spend most of their time on a shallow limestone shelf about 84 square feet in area (a bit larger than two pool tables), where they browse on algae, cyanobacteria, and small invertebrates; court, mate, and lay their eggs.

Pupfish got their common name from fish biologist Carl Hubbs, who was struck by what he thought was their playful behavior. They weren't playing: Hubbs was watching breeding males lunging and nipping at their rivals. The name was good branding, though. It would have been harder to rally public support for the preservation of, say, long-jawed mudsuckers or sarcastic fringeheads. Pupfish could pass for minnows except for their teeth, which true minnows lack.

Many of the hundred-odd known species in the pupfish family are as extremophile as Werner Herzog, living at the margins of the tolerable. According to UC Davis biologist Peter Moyle, their homes include high mountain lakes in South America, desert springs in North America and North Africa, and saline marshes in North America and the Mediterranean region. Some endure temperatures up to 104 F and salinity levels twice that of the sea. Five or six species, depending on who's counting, are scattered across the California and Nevada deserts.

Pupfish life histories follow a live-fast-and-die-young strategy. Few species' members live beyond a year. In good years, their populations boom to phenomenal levels. In Death Valley proper, the Salt Creek pupfish (C. salinus), is confined to a single saline drainage where fish may go through several generations in a year, with counts of over 500 pupfish per square meter of creek-bed and estimated peak populations in the millions. As the creek dries in summer, scavenger birds feast on the fish. The Panamint people of Death Valley traditionally caught Salt Creek pupfish in baskets and baked them.

Even a pupfish can't live without water, and some have been hit hard by diversions and groundwater depletion. A subspecies of the Amargosa pupfish found only at Tecopa Springs was wiped out by the construction of bathhouses. Another, the Shoshone pupfish, was thought to have been driven to extinction when Shoshone Springs was converted to a water supply for the town of Shoshone; a remnant population was discovered in an outflow ditch in 1986, and its descendants were moved to restored habitat in Shoshone. The Owens pupfish was a near-casualty of the diversion of the Owens River to provide water for Los Angeles. At one point in 1970, California Fish and Game biologist Edwin Pister loaded all the surviving members of the species into two buckets, which he then carried to safety across uneven terrain. Fortunately, Pister kept his grip.

Fencing and a warning sign with typo guard the pupfish at Devils Hole | Photo: Ken Lund, some rights reserved

The fish in Devils Hole are a special case. It's possible to account for the distribution of the other pupfish species if you posit ancient post-glacial lakes that covered much of the Mojave before they dried up, leaving the pupfish stranded in their present-day streams, springs, and pools.

But Devils Hole was never part of a lake system. Geologists have established that the pool has been open to the surface only for 60,000 years, after collapsing rocks created a skylight to the aquifer. It's also unlikely that the ancestral pupfish could have reached Devils Hole through the aquifer. The fish have no traits - loss of pigment, reduced vision - typical of fish that have evolved in lightless environments.

Judging by patterns of gene flow, some pupfish have been able to move among normally isolated habitats in the Amargosa River drainage during super-wet years like 1862. However, there is no geological or hydrological evidence that Devils Hole has ever overflowed, allowing pupfish to enter or leave. During the last 116,000 years the water has never been higher than 30 feet above its present level, still 26 feet short of overflow.

Some biologists speculate that eggs adhering to the feet of water birds - a means of transport that Charles Darwin wondered about, in other contexts - might account for the founding population. Others have wondered about Native Americans transporting the fish from another location. They knew the pupfish were there. In 2002, Timbisha Shoshone elder Barbara Durham recalled dangling her feet in the water and letting the pupfish tickle her toes. But there's no tradition of their introduction or use as food. [T]he bottom line is that we really don't have a clue as to how the fish got here, writes Donald K. Grayson of the University of Washington.

The cave entrance: hard to get to even if youre not a fish | Photo: Ken Lund, some rights reserved

However they arrived, how long have they been there? Since they're genetically distinct from all other pupfish, even th

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