Effects of increasing water temperatures on desert fishes and options for management

Authors: Scott A. Bonar

Year: 2013 (xlv)

Abstract

For over ten years, the Arizona Cooperative Fish and Wildlife Research Unit and its partners have studied effects of water temperature on desert fishes. Here I give an overview of that research and report some of the most significant findings, especially those that have implications when managing fish populations for climate change. Unit scientists and their partners studied effects of temperature on 21 fishes found in Southwestern deserts, under either short-term or long-term, static or fluctuating conditions, or combinations thereof. Furthermore, factors affecting stream temperatures were measured and modeled to identify those that managers may be able to alter to cool water bodies. We found some desert fish species resilient to high water temperatures, but the majority were not. Many are less tolerant than some of the nonnative species that compete with and prey upon them. Eggs and older life stages may have different upper temperature tolerances, but upper temperature tolerances of 6 fish species from juvenile to adult life stages either did not vary, or variation was modest. Over a 24-h period, water temperature of desert streams can fluctuate considerably. Survival of three species of desert fish was most related to the midpoint of temperature fluctuations, up to 12^o„aC fluctuations. Modeling and field measurements suggest solutions exist for cooling water bodies to some extent, primarily through modifying the amount of heat entering the system. Unique desert fish species found in isolated springs and fragmented stream systems face particular peril in a warming climate. More opportunities are available for species in wetter climates to move through connected water bodies to reach cooler areas. Desert species, especially those located in isolated water bodies surrounded by vast expanses of desert, have nowhere to migrate if their water body is warmed.