Native Fish in a Bone-Dry River: The Mohave Tui Chub's Slow Comeback

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Mohave tui chub | China Lake Naval Air Weapons Station Photo

You might find the notion that Southern California's Mojave River has a native fish a bit surprising. After all, for most of its 110-mile run from the San Bernardino Mountains out to Baker the riverbed is dry as a bone, its water flowing underground if at all. It hardly seems the kind of place where a fish would do well, and so the existence of the Mohave tui chub — the Mojave River's only native fish — is a bit counterintuitive.

The fact that the Mohave tui chub is on the Endangered Species list, however, isn't even a little surprising. Really, it's only by complete fluke that it isn't extinct.

This incongruous fish is a subspecies — Gila bicolor mohavensis — of the widespread tui chub, Gila bicolor, which ranges from Southern California to the Columbia River watershed. Some tui chub subspecies are faring better than their cousins in the Mojave River, feeding in estuaries along the shorelines of Lake Tahoe or Pyramid Lake.

The Mohave tui chub didn't do as well in the habitat sweepstakes: its native river's flows range from almost zero, most of the time, to thousands of cubic feet per second during floods. Still, the fish is well adapted to the warm, silty, almost saline ponds that historically fringed some sections of the Mojave River, which were scoured out and filled by 10-year floods and then left to slowly turn brackish.

Silvery large minnows averaging about 4-6 inches long at adulthood, Mohave tui chub feed on insect larvae, small fish and invertebrates, and available organic detritus. They spawn in summer: females deposit adhesive eggs on submerged vegetation, laying thousands of eggs in a typical season. Young chub hang out in groups in shallow water; larger adults typically head for any available deeps on their own.

(Incidentally: the lexicographical inconsistency here is not an accident. The Mohave tui chub was given its common name, complete with "h," by biologist Robert Rush Miller, despite being named after the Mojave River. Generally, the "j" spelling for the desert as a whole is preferred in California and Nevada, while the "h" prevails in Arizona. Even though the tui chub's entire range is in California, Miller went with the Arizona spelling for some unknown reason. Not that it was a particular mistake: both spellings are inaccurate transliterations of "Aha Macav," the name by which a prominent Colorado River people called themselves. We now know them as the Mojave. Or the Mohave. Depending.)

When settlers began to dam and divert the Mojave River's meager flows, the fish's habitat declined dramatically. Even worse, people started to introduce bait fish to the Mojave's upper reaches in the 20th Century, including the related arroyo chub. Despite being in some trouble in its native coastal streams — people have gone to some effort and expense reintroducing it to Arroyo Seco, for instance — the arroyo chub did very well in the Mojave's headwaters, displacing and hybridizing with the Mohave tui chub. Our introducing trout, bass, bullfrogs and other species that eat young chubs also didn't help. By the time the chub was listed as Endangered, in 1970, it had been completely wiped out from almost all of its native range.

No one really knows how the fish made it to Mohave Chub Spring, a perennial pond at the farthest downstream reaches of the river. Did a flood in the 1930s wash a few fish into the hole? Were they deliberately moved there by some unknown benefactor? We'll probably never find out. However they got there they managed to survive until 1948, at which point some were transplanted into an artificial pond at Zzyzx, then a privately managed health spa. There, isolated from the habitat disruption and competition that had driven it to within a scale's breadth of extinction, the subspecies survived.

Since then, biologists have attempted to introduce the fish to many new, protected habitats to increase its numbers. Most of these attempts have failed. In the early 1970s a successful new population was started in a wastewater drainage pond network at the China Lake Naval Air Station in Kern County; that population, now numbering somewhere around 6,000, accounts for about half the Mohave tui chub's total numbers. Another successful population was created in artificial ponds at Camp Cady, on the river east of Barstow, in 1987, and yet another on the campus of Apple Valley's Lewis Center, in a pond near the river's upper reaches in 2008. In October, some tui chub were planted in a pond in an open-pit mine in the Ivanpah Valley section of the Mojave National Preserve. How that population will fare remains to be seen.

Endangered Species policy these days is all about getting species off the Endangered list, and management of the Mohave tui chub is no exception. According to the US Fish and Wildlife Service's recovery plan for the Mohave tui chub, downlisting the subspecies from Endangered to Threatened would require that six viable populations be established in the fish's historic habitat, each numbering at least 500 adults, maintained for at least five years, and each having withstood a flood. (Only three of the current populations qualify based on geography.) Taking the Mohave tui chub off the Endangered Species list entirely would require that the fish, in the words of USFWS,

be successfully re-established in a majority of its historical habitat in the Mojave River. Re-establishment means that the populations of Mohave tui chub are viable.

Which seems like a long shot. One obvious candidate for a restored population, Afton Canyon, shows some of the issues involved. At Afton Canyon, the Mojave River flows year-round: shallow bedrock forces the river's flow to the surface. The canyon is thus a famous section of the 4WD playground, the Mojave Road. Early documents discussing recovery of the Mohave tui chub refer to the possibility of establishing a new population in the Afton Canyon Campground Pond. Later discussions center around the fact that the pond had gone missing, filled in by flood-borne silt. The invasive plant tamarisk, which dries up streams throughout the desert, is found in Afton Canyon in abundance, as are the introduced fish Lavinia exilicauda — another ironic invader, seriously threatened in its original northern California range — and hybrids between Lavinia and the arroyo chub. One could eradicate the introduced fish using rotenone or another biodegradable poison, but that would threaten the Canyon's population of native western pond turtles. Even if you could walk that tightrope, you'd still have to contend with the leaking oil pans of the local off-roaders, and then a flood like the one in 2005 could come through and undo all your work, filling in carefully dug ponds and washing arroyo chub down from Victorville.

Still, places like Afton Canyon are critical to the long-term survival of the Mohave tui chub, and restoration for the chub can benefit a lot of other native species — the local bighorn, for instance, who find it easier to get a drink when there's not so much tamarisk.

In the meantime, biologists are working to increase the local populations of tui chub in other places along the Mojave River. You can learn more at The Lewis Center's website.

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published this page in News 2012-06-18 09:57:26 -0700