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Fish Fry: How Will a Warming World Impact U.S. Trout Populations?

Scientists believe that the nearly 5-degree Fahrenheit temperature increase forecasted for the interior West could reduce the trout habitat by half in this century, sending their numbers into a tailspin



Eric Engbretson, U.S. Fish & Wildlife Service

Dear EarthTalk: A fisherman friend of mine told me that trout populations in the interior West of the U.S. are already shrinking due to global warming. Is this true? And what is the long term prognosis for the trout?
—Jon Klein, Portsmouth, N.H.

Most scientists agree that the effects of global warming are starting to show up all around the world in many forms. Throughout America’s Rocky Mountain West, rivers and streams are getting hotter and drier, presenting new challenges for trout already struggling with habitat fragmentation and pollution.

A recent report by the Natural Resources Defense Council (NRDC) and Montana Trout Unlimited (MTU) found that global warming is shrinking cold-water fish habitat, threatening the trout and other fish that depend upon it. Scientists believe that the nearly five degree (F) temperature increase forecasted for the Interior West could reduce trout habitat by half in this century, sending trout populations into a tailspin.

While declines in trout population are bad for local ecosystems and biodiversity, they are also bad for people—especially sport fishers and those employed by the billion dollar recreation industry. In Colorado, sport fishing contributes $800 million to the state’s economy each year and supports 11,000 jobs. In Montana, angling generates $300 million annually. Trout fishing also brings in big dollars to New Mexico, Utah, Wyoming and Idaho. “Hotter temperatures are shutting down our most popular streams during the height of the fishing season,” says MTU’s Bruce Farling. “The closures are becoming an annual event when trout are stressed by warm water and low flows. The implications…are clear: fewer trout and fewer opportunities to fish.”

A U.S. Forest Service (USFS) study found that between 53 and 97 percent of natural trout populations in the Southern Appalachian region of the U.S. could disappear due to warmer temperatures predicted by global climate change models. The three species of trout in question—Brooks, Rainbows and Browns—are already barely hanging on due to road building, channelization and other man-made disturbances.

“As remaining habitat for trout becomes more fragmented, only small refuges in headwater streams at the highest levels will remain,” says biologist Patricia Flebbe of USFS’s Virginia-based Southern Research Station. “Small populations in isolated patches can be easily lost and, in a warmer climate, could simply die out,” she warns, adding that Southern Appalachia trout fishing may become “heavily managed.”

“Trout are one of the best indicators of healthy river ecosystems; they’re the aquatic version of the canary in the coalmine,” says NRDC’s Theo Spencer. “This is our wake up call that urgent action is needed today to reduce heat-trapping pollution that causes global warming.”

NRDC is calling for swift enactment of climate change legislation and for limiting logging and road building near trout streams to ensure enough shade to maintain cooler water temperatures. Also, they say, placing fallen trees and branches and boulders into rivers and streams will help provide shelter for fish and create deeper pools that collect cooler water. Keeping pesticides and fertilizers out of watersheds will also improve the quality of habitat and likelihood of survival for trout species facing an uncertain future.

CONTACTS
: NRDC, www.nrdc.org; MTU, www.montanatu.org; USFS, www.srs.fs.usda.gov

EarthTalk is produced by E/The Environmental Magazine. SEND YOUR ENVIRONMENTAL QUESTIONS TO: EarthTalk, P.O. Box 5098, Westport, CT 06881; earthtalk@emagazine.com. Read past columns at: www.emagazine.com/earthtalk/archives.php. EarthTalk is now a book! Details and order information at: www.emagazine.com/earthtalkbook.

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