USDA Forest Service (FS) research projects that between 53 and 97 percent of natural trout populations in the Southern Appalachians could disappear due to the warmer temperatures predicted under two different global climate circulation models. In an article published October 2 in the online version of the Transactions of the American Fisheries Society, Patricia Flebbe, research biologist at the FS Southern Research Station unit in Blacksburg, VA, maps out trout habitat in a future, warmer climate.
The three species of trout that live in the Southern Appalachians--native brook and the introduced rainbow and brown trout --all require relatively low stream temperatures to survive. Average air temperature in the United States has increased by about 0.6º C (1o F) over the last 100 years, and is projected to increase 3 to 5ºC (5.4 to 9o F) over the next century, causing a corresponding warming of stream temperatures.
"Trout species in the Southern Appalachians are already at the southern limits of their ranges," says Flebbe. "If temperatures warm as much as predicted, trout habitat in the region will definitely shrink."
To estimate trout habitat in relation to higher temperatures, Flebbe and fellow researchers Laura Roghair from the Virginia Tech Conservation Management Institute and former FS employee Jennifer Bruggink produced a regional map of wild trout habitat based on information from stream samples, expert knowledge, and suitable land cover. They then developed a model that uses elevation and latitude as surrogates for temperature, producing spatially explicit information about how much trout habitat will be left as temperatures rise over the next 100 years.
"Estimates of how much temperature will increase in the Southern Appalachians varies according to the global circulation models used, which, in turn, affects projections of habitat loss," says Flebbe. "Using predictions from the Hadley Centre, about 53 percent of trout habitat would be lost over the next century. Under the more extreme model from the Canadian Centre, 97 percent would be lost."
Trout habitat in the Southern Appalachians is already fragmented due to land use change, road building, channelization, and other disturbances. Under both temperature change scenarios, this fragmentation would increase. "As the remaining habitat for trout becomes more fragmented, only small refuges in headwater streams at the highest levels will remain," says Flebbe. "Small populations in isolated patches can be easily lost, and in a warmer climate, could simply die out."
"Although all three of these trout species will probably remain viable in other parts of their range, the world could lose the brook trout strain unique to the region," she adds. "And, as a result, trout fishing in the Southern Appalachians may become a heavily managed experience."
The full text of the article is available online at http://www.srs.fs.usda.gov/pubs/24607