Assessing competition between Razorback Sucker and Flannelmouth Sucker?

Authors: David Rogowski, Pilar Wolters, Cory Nielson

Year: 2021

Abstract

The Colorado River within the Grand Canyon has been altered by the construction of Glen Canyon Dam and Hoover Dam. Over recent years drought has resulted in the lowering of Lake Mead and the re-emergence of an additional 90 km of river. During this time period, Flannelmouth Sucker have experienced widespread population expansion in the Grand Canyon. Currently Flannelmouth Sucker are the most abundant fish species captured in the Colorado River, Grand Canyon, while Razorback Sucker remain exceedingly rare. Although Razorback Sucker have been documented reproducing within the Grand Canyon, we have not captured any juvenile or sub-adults. The differential success of these two catostomids suggest that Flannelmouth Sucker may be competitively excluding Razorback Sucker from the Grand Canyon. To test this we conducted a laboratory experiment investigating growth rates and food conversion rates of juvenile Flannelmouth Suckers and Razorback Suckers at two food levels, and two nominal temperatures: 15 and 20? C. These temperatures reflect contemporary and pre-dam conditions. In addition, we compared species housed singly and together. Higher food levels and warmer temperatures resulted in higher growth rates and improved food conversion rates. Razorback Suckers had greater growth and better food conversion rates than Flannelmouth Suckers across all treatments. Food conversion rates for Razorback Sucker were similar across the tested temperature range, suggesting that current water temperatures within the Colorado River, Grand Canyon are adequate for growth. Surprisingly, Flannelmouth Sucker were not as efficient in converting food into mass at cooler temperatures, particularly in the higher food treatment. Our results suggest that competition with Flannelmouth Sucker does not explain the absence of juvenile Razorback Sucker within the Grand Canyon.