Consequences of an altered thermal regime for Colorado River native fishes

Authors: David L. Ward

Year: 2012 (xliv)

Abstract

In the Colorado River in Grand Canyon a few species of native fish including humpback chub, Gila cypha, flannelmouth sucker, Catostomus latipinnis, and bluehead sucker, Catostomus discobolus, have managed to persist and even increase in abundance in recent years, despite overall declining trends for most other southwestern native fishes. One reason for this unique trend may be the constant low water temperature below Glen Canyon Dam caused by hypolimnetic water releases from Lake Powell. Although cold water year-round is known to be physiologically detrimental to native Colorado River fishes, it may also exclude warm water invasive species that have decimated native fish populations in other areas. When droughts occur, low water levels in Lake Powell allow for warmer water to be released from the epilimnion of the reservoir. Native Colorado River fishes with a long life span may be able to take advantage of rare drought induced warming events and produce strong cohorts that survive. The interval of drought induced warming may play a critical role in the persistence of native Colorado River fishes in Grand Canyon.