Basic Facts About Colorado River Basin Fish

The Colorado River Basin is home to at least 14 native species of fish. Four of these fish are endangered—the Bonytail (Gila elegans), Razorback Sucker (Xyrauchen texanus), Colorado pikeminnow (Ptychocheilus lucius), and Humpback chub (Gila cypha). These fish evolved over millions of years in the Colorado River Basin, and are unique to the ecosystem.

Bonytails

Bonytails are dark gray, silver and white with small heads, large fins and streamlined bodies

Length: 16-18 inches, though some have been known to grow to 2 feet.

Diet: Insects and plant matter.

Lifespan: Bonytails can live as long as 50 years.

Reproduction: Bonytail spawn in spring and early summer at age of 5 to 7 years.

Population: Bonytails are the rarest of the four endangered fish in the Colorado River basin. There are no known reproducing populations in the wild.

Threats: streamflow regulation, habitat modification, competition with and predation by nonnative fish species, hybridization, and degraded water quality.

Razorback suckers

Razorback suckers are brownish-green, white and yellow with a sharp edged hump on their backs. They have fleshy lips that they use to suck up their food. Their hump gives them stability when swimming in strong currents.

Length: Usually 16-18 inches long, though some have been known to grow up to 3 feet.

Diet: Insects, plankton, and plant matter.

Lifespan: Razorback suckers have have been known to live to 40 years or more.

Reproduction: Spawn in the spring at as early as 3 to 4 years old.

Population: The existing population is mainly adult fish, due to high death rates of young fish.

Threats: Streamflow regulation, habitat modification, competition with and predation by nonnative fish species, and degraded water quality.

Colorado pikeminnows

Pikeminnows are olive-green and gold with torpedo shaped bodies. These fish are the largest species of minnow native to North America, they can grow to 6 feet long and 80 pounds or more!

Length: Usually 18 to 22 inches, though some pikeminnows have been known to grow to 6 feet in length.

Diet: Pikeminnow young feed on insects, adults feed on other fish.

Lifespan: Pikeminnows have been known to live to 40 years or more.

Reproduction: Spawn in late spring to early summer at around 5 to 6 years of age.

Population: There are populations in the Green and Colorado Rivers that are stable and reproducing. A small population can be found in the San Juan River Basin.

Threats: Streamflow regulation, habitat modification, competition with and predation by nonnative fish species, and degraded water quality.

Humpback chubs

Humpback chubs are gray or olive with silver sides and white bellies and sport large humps on their backs. Spawning adults have reddish gills.

Length: 14-16 inches.

Diet: Insects, plankton, and plant matter.

Lifespan: Humpback chubs have been known to live to nearly 30 years.

Reproduction: Spawn in spring and early summer at as early as 2 to 3 years of age.

Population: There are 6 known populations that are small but stable.

Threats: Streamflow regulation, habitat modification, predation by nonnative fish species, parasitism, hybridization with other native fish, pesticides and pollutants.

Threats

While western settlers valued the Colorado pikeminnow as food, calling them “white salmon” or “Colorado salmon,” they considered bonytails to be undesirable and began poisoning them in order to introduce other, nonnative species into the Colorado River. Since then the two main threats to the four species of endangered fish have been:

  • Introduction of Invasives: More than 40 non-native fish species have been introduced to the upper Colorado River basin, and prey on native fish and compete with the native fish for resources.
     
  • Water Development: Before the construction of dams and reservoirs, these fish were adapted to short periods of torrential flooding or very low flows and to longer periods of variable but less extreme flow conditions. The river was made of cooler water from snowmelt in the spring and early summer and warmed over the summer months. It also carried a large sediment load throughout the year. Man-made dams and barriers have disrupted river flows and degraded habitats and water quality.

Other threats include habitat degradation and modification, pesticides, and climate change. The most important feature of observed and projected climate changes in the Southwest is the impact on precipitation and water availability. Much of the area is already experiencing a severe drought, and climate change projections indicate that the region will be substantially drier in the future. These changes will have obvious consequences on stream flow in the Colorado River Basin.

Climate changes will also impact the snow pack on which river flows depend. In a region that is already experiencing water conflicts between agriculture, urban water use and ecosystem health needs, climate change will likely necessitate changes in how water is allocated and substantial investments in conservation.

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