Effects of elevated carbon dioxide on fish populations within the Little Colorado River in Grand Canyon

Authors: David Lance Ward, Ben Vaage, Kenneth Sheehan, Clay Nelson

Year: 2016 (xlviii)

Abstract

At base flow, water in the lower 21 km of the Little Colorado River in Grand Canyon comes from springs which are naturally high in carbon dioxide. The effects of high carbon dioxide may structure the fish community and influence recruitment dynamics of endangered humpback chub Gila cypha. We evaluated the effects of elevated carbon dioxide levels on native and nonnative fishes found in the Little Colorado River to determine the potential impacts carbon dioxide may have on the fish population. Laborat ory toxicity trials and field evaluations of humpback chub eggs and larvae were conducted. Humpback chub eggs hatched and larval humpback chub survived above the chute falls complex (rkm 14) at carbon dioxide levels much higher than expected (up to 30 mg/l). Laboratory evaluations of lethal carbon dioxide levels for native and nonnative fishes indicate carbon dioxide tolerances of native and nonnative species are much higher (>60 mg/l) than carbon dioxide levels measured in the lower 16 kilometers of the Little Colorado River. Rainbow trout Oncorhynchus mykiss and smallmouth bass Micropterus doloimeu had the lowest tolerance to elevated carbon dioxide levels (90-100 mg/l) while black bullhead Ameiurus melas and fathead minnow Pimephales promelas had the highest tolerance (200 mg/l). Humpback chub tolerance was intermediate (140 mg/l). We conclude that carbon dioxide dynamics in the Little Colorado River in Grand Canyon are unlikely to have significant effects on the existing fish populatio ns within the lower 16 km of the Little Colorado River.