“If you feel like a fish out of water, just go back in the water.” — Tamerlan Kuzgov

Imagining the cornucopia of species which contribute to the rich natural biodiversity of the North American deserts, fish probably are not what come to mind. Yet, fish are here.

The Mojave Desert provides habitat for at least four fish species: the Mojave Tui chub, and the Salt Creek, Ash Meadows Amargosa, and Devil’s Hole pupfish. In the Sonoran Desert you can find Gila chub, speckled dace, longfin dace, spikedace, loach minnow, Sonora sucker, desert sucker, Gila top minnow, and Quitobaquito pupfish. In the Colorado River there are desert pupfish, humpback chub, bonytail, razorback sucker and Colorado pikeminnow. Pikeminnow sounds like an oxymoron, as pike are typically 2-3 feet long and minnows are usually 2-3 inches long. Turns out pikeminnow can get to as much as 6 feet long!

Then there is the hottest and driest of deserts, the Colorado Desert. Here just the desert pupfish resides. Water in deserts is a precious, finite resource with many competing for access to every last drop. Consequently, all, or nearly all these desert fish are threatened or endangered.

Like amphibians in the desert, desert fish owe their current distribution to the wetter conditions prevalent during the Pleistocene Epoch and earlier. The uplifting of the Colorado Plateau 5-6 million years ago created the Colorado River. While that river eroded its path as it made its way to the sea, during flood events it escaped its banks creating multiple lakes across the Mojave Desert, and repeatedly filled the Salton Sink creating Lake Cahuilla (now called the Salton Sea). There was also the Mojave River with its headwaters in the eastern flanks of the San Bernardino-San Gabriel Mountains, and the Gila and San Pedro Rivers moving water through the heart of the Sonoran Desert. The end of the Pleistocene was marked by a much warmer and drier climate. The rivers left increasingly isolated springs and pools where fish either perished or evolved tolerances to increasing salinity and warmer water. Today pupfish can tolerate waters more than as twice as saline as the ocean. The isolation of each wetland fostered the speciation of fish unique to each remaining pond or river reach.

For all the benefits dams provide, tacitly guarantying water for seemingly unbridled agriculture and suburban growth, damming a river kills the biological richness of that river. The multiple dams now on the Colorado River have nearly erased the fish species that once thrived there. They evolved with and ultimately required the flood and drought cycles that characterized the undammed river. Once the river was dammed, eliminating its erratic flows and leaving it with near constant, controlled flows, the fish could no longer reach their spawning beds. The native fish have largely been replaced by introduced species, species better suited to this constant flow regime. Today the native fish are only hanging on in the upriver reaches above where dams have been built.

Before the dams, periodic flooding occasionally filled the Salton Sink, creating Lake Cahuilla and filling it with its cornucopia of native fish. The Cahuilla people took good advantage of those piscine food resources by building rock fish traps along sections of the lake’s steeper western shore. During those periods when the lake was full and the fish were plenty, the Cahuilla people almost certainly thrived. Today, the only remnant of that native fish community are desert pupfish, confined to the slightly fresher waters of agricultural irrigation drains, and in more natural settings in the Dos Palmas – Salt Creek drainage, and in the Fish Creek -Tarantula Wash area which drains into the southwestern edge of the Salton Sea.

In an effort to protect the desert pupfish from extinction, new populations have been created at the Living Desert Zoo, UC Riverside’s Palm Desert campus, the Coachella Valley Preserve in Thousand Palms Canyon, in Anza Borrego Desert State Park, and at the Dos Palmas Preserve. The criteria for creating such ex-situ refugia is having a dependable body of water with no “contamination” from other fish species, or non-native crayfish. Thousand Palms Canyon seemed to be a perfect choice, except earlier owners had stocked each of the ponds with non-native fish, including mosquito fish, tilapia, bluegills, catfish, bass, and crayfish, with the aim of keeping the ponds crystal clear, free of any algae or other plant growth. Those earlier owners’ intended on developing the canyon into a golf resort, and to attract investors the ponds need to “look pristine.” To be acceptable as ex-situ pupfish refugia all those non-native species had to be removed. To accomplish that objective, the ponds needed to be de-watered, using siphon hoses. No easy task, but doable. Ultimately, after over a year of evaluation to be sure none of the “contaminants” remained, a small number of pupfish were introduced to their new home. For about five years they thrived, but then non-native crayfish were spotted in the pond. The crayfish consumed all the pupfish eggs, and within another two years, all the pupfish were gone. Similar problems have plagued efforts to create ex-situ refugia at the Living Desert Zoo, although they appear to have overcome those setbacks. Those populations at the Dos Palmas Preserve, Anza Borrego Desert State Park, and UC Riverside’s Palm Desert campus have continued to be successful, each one adding a modicum of insurance against the extinction of desert pupfish in California.

As sensitive as pupfish appear to be to “alien invaders,” they can be amazingly resilient to changes in salinity and temperature. They may also be able to overcome temporary drying of their lacustrine habitat. In preparation to move some pupfish to their ultimate ex-situ home at Dos Palmas, about 80 pupfish were kept in a large outdoor cement holding tank. Once the fish were moved, the tank was drained and sat dry for several weeks. After inspecting the dry tank, some cracks were beginning to develop, and so the cement tank was again filled with water. Then a month later, as the tank was being checked to be sure it was holding water, desert pupfish were found happily eating algae and mosquito larva growing in the tank.

How could they have been there? There are two hypotheses. One is that there may have been residual water in the tank’s drain, allowing the fish to survive long enough until the tank was filled again. The second hypothesis is that as in their natural habitat, ponds and streams will occasionally dry up under extreme drought conditions. When that happens either the pupfish go extinct, or perhaps they can lay eggs that are resistant to desiccation, perhaps waiting in suspended animation in damp sand or mud, and then once the water returns, the eggs might then re-hydrate and hatch. There is no evidence that pupfish are able to accomplish such a feat, but if they could it would make a handy adaptation for survival in a fickle desert where surface water may be an ephemeral resource. Regardless of how those pupfish appeared in that tank, desert pupfish, with their abilities to survive the extreme conditions of the Colorado Desert, are a testimony to the power of natural selection.

Nullius in verba

Go outside, tip your hat to a chuckwalla (and a cactus), think like a mountain, and be safe.