Case Studies in Fisheries Conservation and Management: Applied Critical Thinking and Problem Solving

Case 6: What Factors are Related to Condition of Flannelmouth Suckers in the Colorado River?

doi: https://doi.org/10.47886/9781934874189.ch6

The flannelmouth sucker (Figure 6.1) is endemic to the Colorado River, and remains relatively common in the Grand Canyon compared to other native fishes such as the Colorado pikeminnow that has been extirpated from this portion of the river. Your challenge will be to assess body condition (relative plumpness) data for flannelmouth sucker to familiarize yourself with this case, and then develop further questions that delve into the dynamics of this fish species and other members of the fish assemblage in the Grand Canyon.

The study area included in this case study encompasses the Colorado River beginning 26 river kilometers (RKM) below Glen Canyon Dam near the Arizona-Utah border and downstream to Diamond Creek at RKM 363.2 (Figure 6.2). The study site is strongly influenced by Glen Canyon Dam, which has altered flows, reduced and stabilized water temperatures (i.e., reduced summer and increased winter temperatures), and reduced sediment transport. Flood frequency and seasonal variation in flow were greatly reduced after construction of Glen Canyon Dam. In addition, hypolimnetic releases from Glen Canyon Dam have stabilized water temperature at about 10°C (with little warming throughout the 363-km study area) as compared to pre-dam conditions when water temperature varied from near 0 to 29.4°C.

There are several primary tributaries of the Colorado River in Grand Canyon that are important to native fishes, including the Little Colorado River at RKM 98.7 and the Paria River at RKM 1.4 (Figure 6.2). These tributaries are known spawning locations for native fishes, including flannelmouth suckers, and have remained relatively unchanged with regard to flow and temperature regimes, as compared to the mainstem Colorado River.