Trout & Salmon Streams Face Sharp Declines Due to Hotter Temperatures

New Study Predicts Sportfish Species Will Disappear from Many Waterways; Global Warming Means Fewer Fish on Anglers' Hooks

WASHINGTON, DC (May 21, 2002) -- Trout and salmon could disappear from many U.S. waterways due to rising temperatures caused by global warming. Habitats for some species could shrink as much as 17 percent by 2030, 34 percent by 2060, and 42 percent by 2090 if emissions of heat-trapping pollution such as carbon dioxide are not reduced, according to a study released today by Defenders of Wildlife and NRDC (Natural Resources Defense Council).

The sweeping new analysis covers four species of trout -- brook, cutthroat, rainbow and brown -- and four species of salmon -- pink, coho, chinook and chum. Researchers looked at air and water temperature data from more than 2,000 sites across the U.S. Using three internationally recognized climate models, they estimated changes in stream temperature under a variety of pollution scenarios.

"Rising temperatures are increasingly going to curtail the range of trout and salmon in the U.S. That means more and more of our favorite fishing holes will come up empty," said Dr. Daniel Lashof, science director of the NRDC Climate Center. "The reason is pollution from cars and power plants. Fortunately, there are measures we can take now to start solving the problem."

Trout & Salmon in Hot Water

Salmon and trout are coldwater species, acutely sensitive to stream temperature. In many areas the fish are already living at the margin of their tolerance, meaning even modest warming can render a stream uninhabitable. Projected increases in water temperature vary by location, but average 0.7 - 1.4°F by 2030, 1.3 - 3.2°F by 2060, and 2.2 - 4.9°F by 2090, depending on future emissions of heat-trapping gases and which climate model is used. Besides temperatures, timing of summertime highs also changes in some cases, sometimes by as much as four weeks.

The report predicts widespread habitat losses that vary by region. For trout, the most severe losses appear in the South, Southwest and Northeast. For salmon, significant losses are seen throughout their current range, with the biggest impact likely in California.

The extent of predicted habitat loss also varies somewhat by species. For example, if emissions continue to increase at current rates, rainbow trout habitat would shrink by 8 to 11 percent by 2030, 14 to 24 percent by 2060, and 24 to 38 percent by 2090. For coho salmon, by comparison, 6 to 14 percent of habitat could be lost by 2030, 16 to 30 percent by 2060, and 23 to 41 percent by 2090.

For many of the fish species, the effects of global warming come atop a battery of existing problems. Cutthroat trout, native to the Western U.S., have been reduced to less than five percent of their original range and several subspecies are listed as threatened. Wild pacific salmon have disappeared from nearly 40 percent of their historic range in the Northwest, and populations are down more than 90 percent in the Columbia River system. Chinook salmon have been listed under the Endangered Species Act, and several populations of coho are officially threatened.

"Wild trout and salmon populations are already stressed by factors such as loss of habitat to development, competition with hatchery fish, invasive exotic species, and more. Now we must add climate change to the list of challenges they face," said Mark Shaffer, Senior Vice President for Programs at Defenders of Wildlife. "If we don't address the cumulative impact of all these factors, we will see more of these populations switching from a recreational resource to being listed as threatened or endangered."

A High Stakes Problem

An estimated nine million U.S. recreational anglers spend nearly 100 million days fishing each year creating an economic ripple worth billions of dollars. Many of the species covered by the study are regional icons with cultural significance rivaling their recreational and economic value.

"This report warns us not only of losses to natural resources and family traditions, but also that the future of jobs that depend on healthy recreation are at risk," said Steve Moyer, Vice President for Conservation for the group Trout Unlimited. "Our grandchildren and their families may not have the pleasure of fishing for these magnificent creatures in many areas that we know and love today. Billions of dollars per year spent on recreational fishing equipment, guides and resorts may be hit too."

The study covers direct thermal effects on the stream habitats only, and does not examine indirect impacts of global warming such as changes in precipitation or evaporation. It does not include Alaska or Hawaii. Nor does it look at global warming on ocean environments where salmon and some trout species spend much of their lives.

"For many of us, coldwater fisheries are one of the things that make life worth living. This data-rich report asks some sobering questions about yet another area of our lives that may be significantly impacted by global warming," said Paul Hansen, executive director of the Izaak Walton League of America. "Many of the early actions needed to address this problem are very cost-effective, even before we consider the impact on trout and salmon, and can be taken immediately."

Global Warming: What We Know

Global warming is a source of growing concern. Average temperatures have increased by 1.1°F in the past century -- faster than anything seen in at least a thousand years. 2001 was the second hottest year on record, just behind 1998. Since 1990 we have seen nine of the 10 hottest years in history. Although natural causes may be playing a role, most experts believe heat-trapping pollution from cars, power plants and other sources is the main culprit. These emissions collect in the atmosphere, preventing excess heat from escaping, and increasing temperatures here on the ground.

The Intergovernmental Panel on Climate Change -- a 2,500-member body representing international scientific consensus on the subject -- concluded in 1995 and again in 2001 that man-made pollution from fossil fuel combustion and deforestation is driving temperature increases. Asked by President Bush to review the scientific findings, the National Academy of Sciences reconfirmed in June 2001 that heat-trapping pollution is causing both surface and ocean temperatures to rise. The IPCC estimates temperatures will rise 5 - 10°F over the next 100 years.

In the new report, researchers estimate the average air temperatures at sample locations will increase 1.6 to 2.7°F by 2030, 2.6 - 6.7°F by 2060 and 4.5 - 11°F by 2090. These numbers are slightly higher than global average estimates, and consistent with the expectation that increases will be greater over land and at higher latitudes.

Solving the problem means cleaning up the pollution that causes it -- mainly carbon dioxide emissions. Answers include cleaner, more advanced technologies in our vehicles and power plants. Congress is considering legislation called the Clean Power Act that would require power companies to reduce carbon dioxide pollution, along with several other pollutants that are harming fish stocks.

The Natural Resources Defense Council is a national, non-profit organization of scientists, lawyers and environmental specialists dedicated to protecting public health and the environment. Founded in 1970, NRDC has more than 500,000 members nationwide, served from offices in New York, Washington, Los Angeles and San Francisco.

Defenders of Wildlife is a leading nonprofit conservation organization recognized as one of the nation's most progressive advocates for wildlife and its habitat. With more than 430,000 members and supporters, Defenders of Wildlife is an effective leader on environmental issues. For timely information on environmental issues, visit and subscribe to DENLines, a free e-mail alert newsletter.

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Effects of Global Warming on Trout and Salmon in U.S. Streams