Native Fish in Glen Canyon’s Tributary Rivers

Nearly 30 species of fish are known to inhabit the waters of Glen Canyon National Recreation Area (NRA). However, only eight of these species are native, meaning they occurred in Glen Canyon’s waters historically and were not introduced there by people. Fish are an important part of aquatic ecosystems. They are an integral part of food webs; some are herbivores and others are carnivores.

The native Razorback sucker (Xyrauchen texanus).

US Fish and Wildlife Service/Sam Stukel

Fish can be prey to aquatic species and terrestrial species (such as birds and mammals). Healthy fish populations usually indicate healthier aquatic environments. As native fish species are an important part of the systems in which they occur, conserving them benefits the entire system and conserves the region’s biodiversity.

Of the eight native fish species in Glen Canyon, four are federally listed under the Endangered Species Act (razorback sucker [Xyrauchen texanus], humpback chub [Gila cypha], bonytail chub [Gila elegans], and Colorado pikeminnow [Ptychocheilus lucius]), and four are part of a conservation/management effort by four states, including Arizona and Utah (bluehead sucker [Catostomus discobolus], flannelmouth sucker [Catostomus latipinnis], roundtail chub [Gila robusta], and speckled dace [Rhinichthys osculus]). This second group of native species has been studied less than other fish in the region, and, therefore, was one area of focus in our Park Conditions Summary assessment.

To learn more about the non-native fish (sportfish) of Glen Canyon in Lake Powell and in the Colorado River below the dam, click here.

Assessing conditions of fish species

A recent Natural Resource Condition Assessment (NRCA) through the NPS NRCA Program focused on water-related resources located away from Lake Powell and the mainstem Colorado River. NRCAs evaluate natural resource conditions so that parks can use the best available science to manage their resources. Fish were one of five focal resources selected for this project at Glen Canyon.

For the study, ecologists at Utah State University gathered data and information from published and unpublished reports and databases. They used four indicators of condition—water quantity and availability, water quality, biological community, and habitat quality and availability—to assess the four non-listed fish species in the tributaries of interest. The study area included four of the largest tributaries of the Colorado River, the Escalante, Paria, San Juan, and Dirty Devil.

What did we learn?

Water Quantity and Availability

• The natural flow regime (the pattern of flow magnitude, timing, duration, etc.) is critical in supporting the ecological integrity of streams and rivers, and, therefore, the provision of suitable fish habitat. Departures from the natural flow regime can affect aquatic life by degrading the habitat and water quality and reducing diversity and abundance of organisms. Three of the four streams studied (Escalante, San Juan, and Dirty Devil) exhibited moderate departures from natural or historical conditions in total annual flow, seasonal flow, and variability in flow.
• The Paria River, however, did not appear to depart from natural conditions. These results suggest that water quantity and availability has been moderately degraded from natural or historical conditions, and the condition of water quantity and availability is fair.

Water Quality

• None of the four rivers where the fishes occur have significant impacts to water quality, but information is lacking for some types of contaminants (such as mercury). However, some water quality issues do exist. For example, a stretch of the Lower San Juan River within the park is listed as impaired by the Utah Department of Environmental Quality (partially due to the Gold King Mine spill of 2015), and a short stretch of the Paria River within the park is listed as impaired. For these reasons, the condition for this indicator is good/fair.

The Escalante River in Flood September 2010

NPS Photo

Biological Community

• In the upper Escalante River, all four fish species are consistently present and data indicate stable populations. The fish community in this river in the park appears to be in good condition.

• In the lower Escalante and San Juan rivers, some native fish species are absent or severely reduced in numbers, and the community is dominated by non-native species. Therefore, the condition of the community is poor for the lower Escalante and San Juan rivers.

Habitat Quality and Availability

• The four fish species require different amounts of pools, runs, riffles, and low-velocity habitat, and a mix of various substrate features. Because habitat needs vary by species and available data are limited, condition for this indicator is unknown.

What can park managers do with this information and what questions remain?

Roundtail chub (Gila robusta).

US Fish and Wildlife Service/Matthew Patterson

The information obtained in this study can be used to inform park planning and management actions that involve the park’s tributary rivers and the fish and other wildlife in them. The study revealed that while substantial information is available for some of the condition indicators (such as native and non-native fish species occurrence), there are data gaps in other areas (such as for habitat quality and availability). Other questions that remain include:

• do threats from the loss of water sources for fish warrant additional monitoring and management actions?
• How will the small native fishes respond to invasive plant species control/removal along the Escalante River as it is restored to a pool-riffle habitat?

A few things YOU CAN DO to help protect fish:

• Do your part to keep our waterways clean. Help prevent chemicals and other pollutants from entering the water, and properly dispose of waste. Also see the what you can do to help protect springs and seeps section of the Springs and Seeps PCS article.

• Pick up trash near the water when you can. Either participate in organized river or stream clean-ups, or pick up the discarded trash you find on your own.

• Participate in the Brown Trout Bonanza when it occurs. This repeating event at Glen Canyon offers a monetary incentive for the harvest of brown trout (predators of native fish) in particular sections of the Colorado River. See the Glen Canyon NRA website to learn more.

Information in this article was summarized from: Albright J and Others. 2022. Natural resource conditions at Glen Canyon National Recreation Area: Findings & management considerations for selected resources. Natural Resource Report. NPS/SCPN/NRR—2022/2374. National Park Service. Fort Collins, Colorado. https://doi.org/10.36967/nrr-2293112


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