Native Fish in Glen Canyon's Tributary Rivers

Nearly 30 fish species live in Glen Canyon National Recreation Area, but only eight are native — present historically, not brought by people. Fish are central to food webs, as herbivores and carnivores and as prey for aquatic and land animals such as birds and mammals. Healthy fish usually mean a healthy stream, so conserving natives protects the whole system and the region's biodiversity.

The native razorback sucker (Xyrauchen texanus). U.S. Fish and Wildlife Service / Sam Stukel.

The eight natives

The second group has been studied less, so it was the focus here. For the park's non-native sportfish in Lake Powell and below the dam, see non-native fish.

The assessment

A Natural Resource Condition Assessment (NRCA) under the NPS NRCA Program studied water-related resources away from Lake Powell and the main-stem Colorado River; fish were one of five focal resources. Utah State University ecologists pulled together published and unpublished reports and databases, and rated the four non-listed species in four of the Colorado's largest tributaries — the Escalante, Paria, San Juan and Dirty Devil — on four indicators.

Water quantity and availability

A river's natural flow regime — the size, timing and duration of its flows — underpins its ecology and fish habitat; departures degrade habitat and water quality and reduce the variety and number of organisms.

• The Escalante, San Juan and Dirty Devil show moderate departures in total annual flow, seasonal flow and variability.
• The Paria does not appear to depart from natural conditions.

Water quality

None of the four rivers has significant water-quality impacts, though data are lacking for some contaminants, such as mercury. But a stretch of the lower San Juan in the park is listed as impaired by the Utah Department of Environmental Quality — partly because of the Gold King Mine spill of 2015 — and so is a short stretch of the Paria.

The Escalante River in flood, September 2010. NPS photo.

Biological community

• Upper Escalante: all four species consistently present, populations stable — good condition.
• Lower Escalante and San Juan: some natives absent or severely reduced, and non-native fish dominate — poor condition.

Habitat

The four species need different mixes of pools, runs, riffles, slow water and bottom types. With needs varying and data thin, the condition is unknown.

Roundtail chub (Gila robusta). U.S. Fish and Wildlife Service / Matthew Patterson.

What managers can do, and what's still unknown

The results can guide planning for the park's tributaries and their wildlife. Data are good on which native and non-native fish occur, but thin on habitat. Open questions:

• Do threats from lost water sources call for more monitoring and management?
• How will the small native fish respond as invasive plants are cleared along the Escalante and it returns to pool-and-riffle habitat?

How you can help

• Keep waterways clean: keep chemicals and pollutants out of the water and dispose of waste properly.
• Pick up trash by the water, on your own or at an organized clean-up.
• Join the Brown Trout Bonanza when it runs: a Glen Canyon event that pays anglers to harvest brown trout — predators of native fish — in parts of the Colorado River.

Sources

Based on "Native Fish in Glen Canyon's Tributary Rivers," part of the series NRCA 2022: Condition of Glen Canyon's Tributary Rivers and Associated Resources, National Park Service, summarizing 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, DOI; a work of the United States government in the public domain. The fish photographs are by the U.S. Fish and Wildlife Service.