Mohave Tui Chub

Gila bicolor mohavensis

Description

The Mohave tui chub, Gila bicolor mohavensis, is a moderate to large subspecies of the tui chub, 2-3.7 in (5-9.2 cm) long. It has a thick, chunky body with a large head and short snout, an oblique mouth, and short, rounded fins. In older fish, a distinct hump sometimes develops behind the head. This chub is bright brassy-brown to dusky-olive on the sides and bluish-white to silver on the belly. The fins are olive to rich brown.

The Mohave tui chub is similar in appearance to the Endangered Owens tui chub (G. b. snyderi ) and the Lahontan tui chub (G. b. obesa ).

Behavior

The Mohave tui chub is adapted for feeding on plankton and also consumes insect larvae and detritus. It spawns in March or April when water warms to 65°F (18°C) and may spawn again in the fall. Females affix fertilized eggs to aquatic plants, primarily the ditchgrass. Fry form schools in the shallows, but mature fish are solitary. The life span is probably no more than two years.

Habitat

The Mohave tui chub occurs in mineralized, alkaline waters in deep pools or more shallow out-flow streams. It was once found in the mainstream of the Mohave River but prefers lakes and mineral spring pools. Dominant plants in the habitat include ditchgrass, bulrush, cattail, rush, saltgrass. Because it does not withstand flooding well, it is dependent on populations in lakes and pools to replenish fish that are washed downstream and out of the river.

Distribution

The Mohave tui chub is the only fish known to be endemic to the Mohave River basin in southwestern California. During the Pleistocene, the river was fed by three large lakes—Mohave, Little Mo-have, and Manix—which supplied ideal habitat for this chub. When the climate grew more arid and the lakes dried, the Mohave tui chub became restricted to the Mohave River downstream from Victorville, and to a series of springs between Victorville and the river sources.

The Mohave tui chub is currently found in three extensively modified pools at Soda Springs, situated near the southeastern edge of the dry bed of Soda Lake in San Bernardino County. The springs were an important water stop for travelers on the Mo-have Road, which was a supply road from Los Angeles to Ft. Mohave on the Colorado River. In 1940 Lake Tuendae, the largest pool, was excavated and channeled for a health spa which operated until 1974. Groundwater pumping has decreased the size of the other pools.

In the 1970s Mohave tui chubs were transplanted to Lark Seep Lagoon on the China Lake Naval Weapons Center. This is now the largest existing population, consisting of several thousand individuals. The Desert Research Station Pond near Hinkley, about 10 mi (16 km) northwest of Barstow, supports a transplanted population of 1,500-2,000.

Threats

When the Arroyo chub (G. orcutti ) was introduced as a baitfish into the Mohave River during the 1930s, the Mohave tui chub entered a precipitous decline. The two fish interbred so extensively that the Mohave tui chub was almost eliminated as a unique subspecies by 1967. In addition, construction of dams and reservoirs at the headwaters altered water flow in the mainstream and provided better habitat for many non-native fishes, which compete more aggressively for food.

Conservation and Recovery

After a string of failures, the success of recent relocation efforts has generated cautious optimism for the recovery of the Mohave tui chub. The U. S. Fish and Wildlife Service plans to establish three more protected populations of at least 500 fish each. Likely transplant sites are along the Mohave River at Camp Cady Wildlife Area, Afton Canyon Campground, and Mohave Narrows Regional Park. Once these transplants are deemed successful, biologists will consider removing this chub from the federal list. Biologists are currently assessing the feasibility of removing the Arroyo chub from the Mohave River and restocking the river with the indigenous Mohave tui chub.

Contact

Regional Office of Endangered Species
U.S. Fish and Wildlife Service
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232
http://pacific.fws.gov/

References

Hoover, F., and J. A. St. Amant. 1983. "Results of Mohave Tui Chub, Gila bicolor mohavensis, Relocations in California and Nevada." California Fish and Game 69:54-56.

U.S. Fish and Wildlife Service. 1984. "Recovery Plan for the Mohave Tui Chub, Gila bicolor mohavensis." U.S. Fish and Wildlife Service, Portland.