Effects of climate warming on fish thermal habitat in streams of the United States

The effects of climate warming on the thermal habitat of 57 species of fish of the U.S. were estimated using results for a doubling of atmospheric carbon dioxide that were predicted by the Canadian Climate Center general circulation model. Baseline water temperature conditions were calculated from data collected at 1,700 U.S. Geological Survey stream monitoring stations across the U.S. Water temperatures after predicted climate change were obtained by multiplying air temperature changes by 0.9, a factor based on several field studies, and adding them to baseline water temperatures at stations in corresponding grid cells. Results indicated that habitat for cold and cool water fish would be reduced by -5O%, and that this effect would be distributed throughout the existing range of these species. Habitat losses were greater among species with smaller initial distributions and in geographic regions with the greatest warming (e.g. the central Midwest). Results for warm water fish habitat were less certain because of the poor state of knowledge regarding their high and low temperature tolerances; however, the habitat of many species of this thermal guild likely will also be substantially reduced by climate warming, whereas the habitat of other species will be increased. The threat of global climate change has stimulated the publication of numerous research papers dealing with the potential effects of surface and groundwater warming on the thermal habitat of freshwater fish (e.g. Coutant 1990; Magnuson et al. 1990; Meisner 1990; Stefan et al. 1995). With few exceptions (e.g. Shuter and Post 1990), most of these studies deal with responses to temperature in single water bodies or small geographic regions, so we decided to attempt an assessment of effects at a much larger scale consisting of the lower 48 states. Most of the studies cited above also dealt with effects of climate change on lake fish or habitat. We expected that using less detailed input data would keep the analysis manageable, but that we would use information compiled for or generated from previous smaller scale studies. These existing data include a quality-assured database of historical surface water temperature maxima at U.S. Geological Survey (USGS) stream monitoring stations and maximum temperature tolerances estimated from a field database for several dozen freshwater species of fish, as reported by Eaton et al. (1995); results of analyses of the relationship between air temperature and stream-water temperatures (Stefan and Preud’hommc 1993; Sinokrot and Stefan 1993); and a