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November 28, 2000
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An Upstream Battle
| Breakthroughs for Salmon |
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Last month, United States Secretary of the Interior Bruce Babbitt helped construction workers rip out a section of the 200-foot tall Matilija Dam on the Ventura River in southern California. It is the largest dam removal project in the world. The Matilija is just the latest stop on Secretary Babbitt's recent dam-busting tour in California. A few weeks earlier, sledgehammers pounded the Seltzer Dam near Redding in northern California. Similar scenes are occurring along other creeks. "The removal of these dams will represent acts of creation, not destruction," said Secretary Babbitt. Since early last century, dams have controlled river flooding, provided irrigation, and created electricity in many states, particularly in the West. But environmental advocates say that the current dismantling of some dams will restore the vitality of long-declining river ecosystems. The biggest winners are the rivers' salmon and other anadromous fish—species that return from the salty sea to spawn, or reproduce, in freshwater. For decades, dams have contributed to the rapid depletion of anadromous fish populations from coast to coast. Dams interrupt the natural rhythm of fish life cycles as they swim from river to ocean and back. Adult salmon spawn in gravel beds of rivers and streams—amazingly, the exact same place where they hatched six months to seven years earlier. But the odds are stacked heavily against their return. Some salmon species swim hundreds or even thousands of miles to return home. Only a tiny fraction of adult fish ever reach their spawning grounds. Since salmon don't feed once they leave the ocean, many die from lack of stored body fat. Many others are caught in fishing nets or by a variety of predators. Others choke in the polluted waters near cities. Some salmon eventually do make it back to their home rivers, only to be blocked by huge dams. How steep are the odds against any salmon egg's hatching, surviving, and spawning? Consider that each female adult lays between 1,500 and 10,000 eggs. Only a handful of these—an estimated 0 to 10—will survive to spawn. |
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For more than a century, dams have blocked salmon from returning "home" to spawning grounds.
How can plans to tear down some of these dams affect salmon survival?
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| Problems on the Columbia |
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But in the nineteenth and early twentieth centuries, overfishing and habitat destruction from farming, grazing, mining, logging, and construction took their toll. Then, the Bonneville Dam was built in 1938, and the Grand Coulee Dam followed in 1941. These and other dams cut Columbia salmon runs to a fraction of previous levels. The graph below shows how the salmon population on the Columbia River has changed since 1770. The green bars on the graph represent high population estimates, red bars represent low population estimates, and blue bars show medium estimates.
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The current battle in the Pacific Northwest to save salmon in the Columbia River is looming as one of the most important in the nation. The 2,044-kilometer (1,270-mile) long Columbia runs from British Columbia through Washington before reaching the Pacific. The river was once teeming with salmon.
| The "Four H's" |
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Dam-removal campaigns are now underway from New England to California. Environmentalists hope increased public concern for the salmons' plight will help turn the political tide in their favor. They have identified "Four H's"—areas to focus public awareness.
The reality is that many of our nation's dams will likely remain for decades. In some parts of the country, farmers rely on the crop irrigation that dams provide. In other areas, there are no immediate alternatives to hydroelectric power. "We're not taking aim at all dams," says Interior Secretary Babbitt in the article "Rivers Reborn," on the Web site of the environmental group Friends of the River. "But we should strike a balance between the needs of the river and the demands of river users." Scientists are also busy developing technologies that will help make dams safer for salmon. At the Pacific Northwest National Laboratory, scientists are perfecting a kind of "bionic" salmon. These 6-inch long polycarbonate-coated "fish" are imbedded with tiny sensors that measure stress from water turbulence as the fish "swim" through a dam. They are helping scientists gather clues about the tough conditions salmon must endure to get through dam turbines. The data gained will help scientists design safer turbines and prevent injuries to real salmon. |
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