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USGS Fishing for Success in the Grand Canyon
Released: 3/4/2003

Contact Information:
U.S. Department of the Interior, U.S. Geological Survey
Office of Communication
119 National Center
Reston, VA 20192
Steven Gloss 1-click interview
Phone: 206-220-4573

Denny Fenn
Phone: 928-556-7894



NOTE TO NEWS EDITORS: Photos listed below can be downloaded.
1. ftp://ftp.gcmrc.gov/data/press/electrofishing.tif (electrofishing on the Colorado River)
2. ftp://ftp.gcmrc.gov/data/press/ChubNHand.tif (humpback chub)
3. ftp://ftp.gcmrc.gov/data/press/science_camp.tif (science camp on banks of the Colorado River)
4. ftp://ftp.gcmrc.gov/data/press/LCR%20Confluence.tif (confluence of Little Colorado River with Colorado River)

It’s 6 in the evening on February 12 at a sandy campsite on the banks of the Colorado River in northeastern Arizona. A crew of 18 is assembled 50 river miles downstream of Lees Ferry in the Grand Canyon of the Colorado River. The sun has disappeared long ago from the steep canyon walls, and nighttime temperatures hang at a cool 40 degrees Fahrenheit.

As darkness descends, Lew Coggins and Mike Yard, with the U.S. Geological Survey’s (USGS) Grand Canyon Monitoring and Research Center in Flagstaff, Arizona, give final instructions to the science staff, boatmen, and a Native American observer. Poised on the shore is a fleet of rafts and aluminum boats fitted with electrodes, lights, generators and 50-horsepower outboard motors. The canyon reverberates with noise as two boats jump to life and head upstream. Two more do the same and head downstream. A fifth boat stands ready to run relays between the two teams to collect fish and conduct sampling of drifting invertebrates.

Nighttime fishing has begun.

The Grand Canyon Monitoring and Research Center is conducting an innovative study aimed at helping to restore the endangered humpback chub, a fish that can reach up to 18 inches in length and whose only native home is in this basin. The study, said Steve Gloss, the lead scientist on the project and the Program Manager for biological resources at the Grand Canyon Monitoring and Research Center, is part of a new effort to address sediment loss and fish management in the majestic Grand Canyon.

"We want to determine if non-native fish, particularly rainbow trout, in the Colorado River System are major factors contributing to a serious decline in humpback chub abundance," said Gloss. "We suspect that these invasive fish are not only eating the chubs and other native fish, but are also competing for habitat and food."

The humpback chub once thrived in abundant numbers in the warm, sediment-rich waters of the Colorado River Basin before the building of Glen Canyon Dam 40 years ago. Appropriately named, the humpback chub has a small head and snout, a streamlined gray body streaked with silver, and a prominent hump along its back. Researchers believe that this hump helps stabilize the fish as it copes with the Colorado River’s turbulent flows. But in 1992, the abundance of one-year-old humpback chub took a nosedive, a decline that has persisted and which researchers believe will continue unless conditions change. Additionally some other native fish, like the razorback sucker, are no longer found in the river within the Grand Canyon, whereas others, like the flannelmouth sucker, are believed to be declining.

Over the last decade, the humpback chub has declined in the Grand Canyon from around 8,000 in 1993 to around 2,000 or fewer adults in 2001. Resource managers find this decline particularly disheartening because a 1996 decision, based on the best information available then, modified the operation of Glen Canyon Dam in an effort to improve the condition of the habitat and the native species that call the canyon home. These changes in dam operations do not appear to have helped the native fish species, as was hoped.

In contrast, since 1996, the non-native trout population in the Grand Canyon has tripled to more than one million fish due to cool, clear water and stable habitat conditions, which appear to favor trout but not the chub. Glen Canyon Dam retains 95 percent of the river’s sediment. Water released through the dam is clear and cold, and the flow volumes are heavily regulated.

Although many factors could be contributing to the chub’s continued decline, scientists are focusing in this study on the effects of non-native trout on the chub.

"We want to see if we can reduce the non-native trout population through fishing, and if so, how that changes populations of humpback chubs and other native fish in the river," Gloss said. "We also will use this as an opportunity to examine the diet of these trout and the availability of food items for fish in general."

USGS biologists will remove non-native fish, primarily rainbow trout, from 10 miles of the Colorado River centered on the mouth of the Little Colorado River, where the highest abundance of adult and young chub occur in the mainstem of the Colorado River. The Bureau of Reclamation, working with USGS scientists, will also attempt to disrupt trout breeding and habitat by varying the flow from Glen Canyon Dam during the trouts’ winter and spring spawning and rearing seasons from January to March.

It’s now about midnight on the river, and the boats upstream have completed "electrofishing" their portion of the river. In near synchrony, the two boats maneuver down opposite shores of the river, guided by the expertise of some of the best motorboat operators in the Grand Canyon in some of the most innovative whitewater boats available. Intermittently the crews pass a mild current of electricity through the water to temporarily stun the fish in the river. The stunned fish float to the top and are netted by an observer poised over a railing at the front of the boat. In this control section of the river, both native and non-native fish are quickly identified, measured, weighed, and released. Large rainbow and brown trout are tagged with plastic, individually numbered tags before release. Downstream, the two other boats are doing the same.

"From this sampling," said USGS fish biologist Lew Coggins, "we can estimate the relative numbers and size groups of native and non-native fish populations."

During the next 10 nights, additional fishing will take place starting four miles below the control section in what the researchers call "removal reaches." In this 10-mile stretch of river, the crew will catch, measure, and then release native fish. Non-native fish, though, will be caught, measured, humanely euthanized in a bath of carbon dioxide, and transported back to camp. Then their stomachs are removed and preserved for an evaluation of predation on native fish. Native Americans will receive the fish bodies to be used for fertilizer.

These fishing trips, according to Denny Fenn, Director of the USGS Southwest Biological Science Center, will occur once a month in January, February, and March and then again in July, August and September. The plan is to repeat this over multiple years. The crew does the fishing at night to maximize the catch. "In the day", said Gloss, "the boats would spook the fish because the water is usually so clear."

In the first trip from January 15-31, the crew caught 4,512 fish, of which 90 percent were rainbow trout. So far one of the more interesting moments of the study was when researchers caught a rainbow trout with a flannelmouth sucker in its mouth. Said Coggins, " In the control river reach one crew caught and tagged a rainbow trout and released it. Ten days later we caught the same trout 15 miles downstream with a live flannelmouth sucker in its mouth. We carefully extracted the sucker from the trout’s mouth, held it briefly in water to revive it, and let it go. That trout told us two things, first that at least some trout eat native fish, and second, some trout move a considerable distance in the canyon in a fairly short time. This study is designed to move us beyond such singular observations to credible generalizations."

The human footprint in the canyon also is a concern. Mike Yard, who ran rafting trips through the canyon before becoming a USGS aquatic biologist, said, "Eighteen people, eight boats with motors, and generators running at night to power the electroshockers in the canyon can interfere with the wild experience visitors seek in the Grand Canyon. Our partner, the National Park Service, is as concerned about this as we are, and they evaluate and approve every trip me make. Also, we use boats with motors to help us get into and out of the canyon as fast as possible. We want to respect the beauty and peace of the area."

The Grand Canyon is an important spiritual place for some Native Americans. Therefore, the USGS invited representatives of Native American Tribes with cultural ties in the canyon to participate in the research. Some tribal representatives, in discussion with the USGS, noted that they did not want an "aura of death" in the canyon. Says Fenn, "Because of these concerns we abandoned our original plan of grinding up the non-native fish and putting them back in the river. Now on every trip, we put the remains of the dead trout in large plastic bottles and boat them out, and then give the fish to the Hualapai Tribe. The tribes are more comfortable with this research now that a beneficial use has been found for the trout."

Greg Glassco, the Cultural Director of the Hualapai Tribe, said, "We received 285 gallons of ground fish from the first trip, which we have used for composting and fertilizing household and community gardens. The tribe is eager and willing to take more, and is considering drying some, maybe experimenting with manufacture of fish emulsion, and sharing with other tribes."

This research is conducted through the Glen Canyon Adaptive Management Program, which was established to help incorporate scientific advances into management decision-making. This program is a collaboration in science and management for the 293 miles of the Colorado River between Glen Canyon Dam and Lake Mead. The group, comprised of stakeholders affected by operation of Glen Canyon Dam, makes recommendations to the Secretary of the Interior on dam operations. The experimental fish removal meshes well with several of the program’s goals, particularly the desire to maintain or attain viable populations of existing native fish, reduce risks for humpback chub and razorback sucker, and prevent adverse modification to their critical habitat.

The USGS supports this project, with key partnerships with the Bureau of Reclamation, National Park Service, and the Native American Tribes of the Grand Canyon.


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