Hot, cold, and hungry suckers

Authors: Pilar Wolters, David Rogowski, Corwin Nielson

Year: 2019

Abstract

The Razorback Sucker, Xyrauchen texanus, is an endangered endemic fish of the Colorado River basin. Recovery efforts include nonnative fish removals, habitat improvements, and population augmentation. All populations are still augmented by stocking except for the Lake Mead population on the Arizona-Nevada border and the Colorado River in Grand Canyon, Arizona. Adult and larval Razorback Suckers have been detected in the Colorado River within the Grand Canyon, however recruitment has yet to be documented. The Colorado River in Grand Canyon is largely dominated by the Flannelmouth Sucker, Catostomus latipinnis, another native sucker species. We hypothesized that Razorback Sucker recruitment may be negatively affected by competition with Flannelmouth Sucker. To test this hypothesis, we conducted a competition experiment with young of year fish at different temperatures and feed levels. We had four replicates of six different treatments: Flannelmouths at high and low feed, Razorbacks at high and low feed, and both Flannelmouths and Razorbacks at high and low feed. The experiment was conducted in two phases, each eight weeks in length. The cold phase (15 C) was first followed by the warm phase (20 C) with a one week acclimation period between phases. In the experimental treatment (Flannelmouths and Razorbacks together at low food) the Razorbacks gained weight at 15 C while the Flannelmouths lost weight. We did not see this pattern at 20 C. This preliminary result suggests that the presence of Flannelmouth Sucker may not be negatively affecting Razorback Sucker recruitment (at 15 C), or that limitations on Razorback recruitment within the Grand Canyon are occurring before they reach 30mm total length in the wild.