Back to the future, warmwater fish in the Grand Canyon

Authors: David Rogowski

Year: 2022

Abstract

The Colorado River was historically a warmwater system until dams were installed. Prior to Glen Canyon dam the most common fishes were Channel Catfish and Common Carp. After the dam cool water releases reduced the number of these two nonnative species, but they still were very common from 2000-2010. Around 2010 as water levels began declining in Lake Powell and Lake Mead, the abundance and distribution of these two species within the Colorado River, Grand Canyon also declined. The decline occurred in part due to the formation of Pearce Ferry Rapid, and potentially the loss of warmwater backwater areas in western Grand Canyon as Lake Mead shrank and the Colorado River re-emerged. As Lake Powell declines the release water has increased and areas formerly to cold for reproduction of a variety of species are now within their reproduction range. In 2022 Common Carp, Green Sunfish, and Smallmouth Bass successfully spawned in a slough three miles below Glen Canyon Dam. What does the future hold for the Colorado River native fish assemblage when water temperatures are now within the range of a variety of nonnative fish that are relatively common within Lake Powell and Lake Mead? Will it return to a system dominated by nonnative fish again?