FISH

The Colorado River and its tributaries, including the Green and San Juan Rivers, drop more than 2 miles as they flow from mountains in Wyoming, Colorado, and New Mexico to the Gulf of California. The Colorado has seasonally variable temperatures and radical fluctuations in flow, historically ranging from a few thousand to nearly 400,000 cubic feet per second.

Only fourteen species of fish originally inhabited the unique ecosystem of the upper basin of the Colorado River. Three-quarters of these fish are found in no other river basin. At present, four of those fish are listed as endangered: Bonytail Chub, Colorado Pikeminnow, Humpback Chub, and Razorback Sucker. More than forty alien species now live in these waters.

In the last 50 years, human changes to this river system have altered the seasonally variable flows, created large lakes behind dams, and led to hundreds of miles of cold water below the dams, all of which have contributed to habitat loss and a decline in species numbers.

The introduction of alien fish to the Colorado River has had a significant negative impact on the native fish, too. One study at the confluence of the Green and Colorado Rivers found that 95 percent of the fish species were nonnative. Channel Catfish are particularly damaging as they eat young Pikeminnows and the eggs and larvae of Razorback Suckers.

Although one rarely sees fish in the Colorado River, nine species are described in this section. The two most commonly encountered species are the Carp and Channel Catfish. Common and scientific names come from Common and Scientific Names of Fishes from the United States, Canada, and Mexico, 7th Edition, American Fisheries Special Publication 34. Author note: Unlike what happens with the names of mammals and plants, ichthyologists prefer that all fish names be capitalized, a practice I have adopted throughout this book.

BLUEHEAD SUCKER

Catostomus discobolus

Sucker family (Catostomidae)

6–10 in., blue head, bluish gray back, white belly

Blueheads are native to the upper Colorado River drainage system. Their preferred habitat is in the fast-flowing sections over cobbles, where they can use a cartilaginous chisel on their mouths to scrape algae and bugs off the bottom. The mouth of all members of this family is under the fish, allowing them to feed effectively on the bottom substrate. Blueheads are common and widely distributed.

FLANNELMOUTH SUCKER

Catostomus latipinnis

Sucker family (Catostomidae)

18–24 in., weight up to 4 lb., greenish-gray back and upper sides, lower sides yellow or orange-red

Flannelmouths are big river fish. They have not suffered as much of a population decline as other natives. Along with Bluehead Suckers they are the most common species caught in drift nets in the upper Colorado River. They inhabit shallow riffles as young and deep riffles as adults. Flannelmouths have only a short upstream migration. Like other suckers, they eat algae and insects off the river bottom. They may have been a primary component of the Pikeminnow diet.

RAZORBACK SUCKER

Xyrauchen texanus

Sucker family (Catostomidae)

Up to 36 in., weight up to 16 lb., brownish green with whitish belly, abrupt bony hump on back

Razorbacks were once plentiful enough to be commercially harvested. Now they are limited to a large but dwindling population in Lake Mojave and smaller groups on the Green River near Dinosaur National Monument and on the Colorado River near Colorado National Monument. Razorbacks have a sleek body and a thin, humped back, excellent adaptations for the fast, turbulent water of the Colorado River. Similar to the other endangered native fish, Razorbacks have been unable to adapt to the dam-caused changes and introduction of nonnative fishes.

COMMON CARP

Cyprinus carpio

Carp and minnow family (Cyprinidae)

Up to 30 in., weight up to 10 lb., large bronze scales, very short “whiskers”

Carp live in shallow water. During the spring and summer, they often congregate in groups to spawn in water less than 4 feet deep. They eat almost anything by taking in mouthfuls of the bottom substrate, gleaning invertebrates, and spitting out sediments, a process that tears up the fragile bottom, actively degrading habitat.

Carp are native to Asia. The US Bureau of Fisheries billed carp as the greatest food fish ever and shipped them across the country by rail following the Civil War. They reached Utah around 1888.

HUMPBACK CHUB

Gila cypha

Carp and minnow family (Cyprinidae)

Up to 20 in., olive-colored back, silver sides, white belly, small eyes, long snout that overhangs jaw

Humpback Chub are so rare that they were not discovered by scientists until ichthyologist Robert Rush Miller found one in a collection at Grand Canyon National Park. They were federally listed as endangered in 1973. Humpbacks, as their name suggests, have an unusual dorsal hump found in no other fish. This feature, combined with their torpedo-shaped body, helped the fish survive in the turbulent, swift water found in the Colorado River canyons. Humpbacks, though, have not been able to adapt to the clear, cold, silt-free waters that flow out of the dams on the main body of the river. They are now limited to Desolation Canyon on the Green River, Black Rocks and Westwater Canyon on the Colorado River, and at the confluence of the Little Colorado and Colorado Rivers.

BONYTAIL

Gila elegans

Carp and minnow family (Cyprinidae)

Up to 20 in., olive-colored back, silver sides, white belly, large fins, streamlined body very thin in front of tail

Bonytails have been federally listed as endangered since 1980. At present, only a few 40- to 50-year-olds are found in Lake Mojave, below Hoover Dam. A few live in hatcheries, while 2,000 5- to 6-inch-long Bonytails were stocked in the Colorado River near Moab in 1996–1997. They live in backwaters and eddies. Ichthyologists suspect that Bonytails may have been an important part of the Pikeminnow diet.

ROUNDTAIL CHUB

Gila robusta

Carp and minnow family (Cyprinidae)

10–14 in., weight 1–2 lb.

Roundtail Chub numbers are down, but they are faring better than the other two Gila species in the system. They are protected in Utah because they are so hard to distinguish from their endangered relatives. Roundtails are carnivorous, opportunistic feeders that eat insects and other fish. They prefer murky waters and silty, sandy, gravelly, and rocky substrates.

COLORADO PIKEMINNOW

Ptychocheilus lucius

Carp and minnow family (Cyprinidae)

Historically up to 6 ft., weight more than 100 lb., present fish up to 2 ft., olive-green back, silvery white belly, mouth extends to back of eye

For the past few million years, until recently, Colorado Pikeminnow reigned supreme in the Colorado River basin. In a typical year the fish migrated up to 200 miles through whitewater rapids to spawn in quiet, warm backwaters. Food was not a problem; if it was smaller, it was dinner. When you are a 6-foot-long fish and weigh over 100 pounds, everything is smaller. But life for this predator is not what it used to be.

Pikeminnow, once plentiful enough to be pitchforked out of irrigation canals in Arizona, have now been extirpated in more than 75 percent of their habitat. Dam-created habitat degradation has fragmented the fishes’ historic migratory routes. Dam building has also severely curtailed the river’s dramatic spring floods, which the fish require for spawning. Habitat loss and introduction of nonnative species created the perfect recipe for this species’ decline.

Old-timers called Pikeminnow “white salmon,” a probable allusion to the fishes’ migratory habits. The American Fisheries Society changed the name of the Colorado Squawfish to Colorado Pikeminnow in 1999 because the former name was offensive to many Native Americans and because P. lucius is a member of the minnow family and has a pikelike body.

CHANNEL CATFISH

Ictalurus punctatus

Bullhead catfish family (Ictaluridae)

Up to 36 in., weight 25 lb., spines on dorsal and pectoral fins for protection

Channel Catfish were also introduced into the Colorado River around 1888. They live in moderately swift parts of the river system. During the day they hide in sheltered spots and feed in riffles at dusk. In early summer after a mayfly hatch, Catfish, with their characteristic “whiskers,” can be seen sucking bugs off the water’s surface. Catfish eat anything, including the young of several native fish species. They are a significant contributor to the decline of native fish populations.