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How dams affect salmon migration

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How dams affect salmon migration

The 1,000 plus species of Salmon and Steelhead that live off the western coast of the United States and breed in the rivers and tributaries of California, Washington, and Oregon have greatly fallen in population. 106 species have become extinct and 314 more are at risk of extinction in the Columbia River Basin, the focus of this report. The causes of this are dams on the rivers stopping salmon from breeding and smolt from returning to the ocean, and commercial fishing boats depleting mature populations and blocking river mouths. The solution to commercial fishing problems is obvious, though not likely to happen,as the government won't go farther than lightly regulating commercial fishing boats, but there are several different approaches to allowing the salmon to breed and smolt to return to the ocean despite the dams, though no effective measures have been implemented due to cost or effects on energy and agriculture. Also, more recently, escaped Atlantic Salmon from aquaculture cages and their offspring are now competing with the native salmon. How depleted are native salmon and Steelhead populations, what has been done so far to boost the populations and has it been effective, and what can be done with dammed river to allow natural breeding?

"Salmon Migration: Decisions, Decisions" no author Environmental News Thursday,

February 18, 1999

"Columbia River Salmon Protection OK'd" no author Environmental News Tuesday, June 30, 1999

"Dam Busting Not Always the Best Decision" no author Thursday, December 31, 1998

"Columbia River Dams and the Decline of Northwest Salmon" A project developed by April Brenden, Laura Fetherston, Jonette Ford, and Shannon Nichols (Group 30), Biology 130 students at University of Oregon.

Since early times, the rivers of the Pacific Northwest have been filled with salmon. In 1894 Richard Rathbun of the Smithsonian Institute traveled west and commented that the quantities of salmon which frequented these waters was beyond calculations, and seemed so great as to challenge human ingenuity to affect it in any way. This is far from being true now. If a person traveled to the Pacific Northwest in 1995 they would find rivers with large dams and non-native hatchery fish. Before the dams, it was estimated that 10 to 16 million wild salmon and steelhead returned to their native spawning grounds. It is now estimated that only 2.5 million return. Of these 2.5 million fish, only one fourth of them ever make it back to their original spawning grounds. These remaining fish are raised in hatcheries. Salmon must be able to migrate upstream from the ocean to reproduce in fresh water. Hydroelectric dams have essentially changed the migration pattern of fish. Dams alter the temperature and flow regimes of rivers; they are barriers to migrating organisms such as salmon, and to the natural movements of sediments, nutrients, and water. In the past, a young salmon's journey to the ocean took two weeks; now it takes two months. Of all the salmon killed by human activity, habitat modifications - principally dams and reservoirs - kill an estimated 99 percent. Downstream migration over a dam is attended by risks of abrasions on the spillway, change in pressure through turbines, concussion at the tailrace, and the "bends," caused by the supersaturation of the tailwater released from depths in a reservoir. Dams have also increased predation of smolts and made gas bubble disease common. Many devices have been investigated for their potential for guiding downstream migrants into unsafe bypasses, using, for example, noises, oxygen bubbles, lights, louvers, and screens. The costs of the installation and their indifferent success has discouraged the notion that high or large dams can be reconciled with salmon production.

The Colombia River system is stitched with hydroelectric dams that produce the countries cheapest power, 40 percent cheaper than the national average. This cheap electricity is why most people are overlooking the salmon runs that are rapidly decreasing. Long-term preservation goals can be overridden by a short-term drive for profit and jobs. Local politicians are always trying to get congress to give them money to build more dams. It's a tradition in this part of the world, one which has been repeatably successful: the waiting game of exploiters. On one side, are the environmentalists, who want to save the salmon runs. The other side, is filled with people in favor of cheap electricity that the Pacific Northwest enjoys. Salmon are headed for extinction in part, because of hydroelectric power. However, federal dams are primarily responsible for the reduction of the pacific Northwest salmon population from about 16 million to 300,000 wild fish each year; even though the federal dams claim they are designated for balanced use of water resources. It is shown in brochures by the US Army Corps of Engineers and at dam visitor centers that the dams are totally safe and easy for fish to pass through. Serious fish passage problems occur at the Colombia River and many others. Hydroelectric dams are a major factor in further declines.

For thousands of years the Columbia River was just that, a river. Now we have changed all that by adding huge dams. Today, what was once the wild and vibrant Columbia river, is just a series of slow, warm lakes. This is not the natural habitat of the pacific northwest salmon that once filled the river. The change in the Columbia River from a fast flowing river into still ponds has affected the salmon in three major ways. The first way is by changing the temperature of the river and streams inhabited by the salmon. Because the water is no longer moving at the same speed it once did and instead is at a virtual stand still, the water is allowed to be warmed up by the sun. Salmon smolts are very susceptible to heat and often the temperatures in the streams reach lethal levels. The second problem created by damming the rivers and impeding the flow, is that the smolts now have an even tougher time migrating downstream. The smolt used to be able to use the "flow" of the river to help them reach the ocean quickly and safely. Now, because there is no "flow" up to 90% of the juvenile salmon are killed even before they reach the ...

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Keywords: how do salmons migrate, how do dams affect aquatic wildlife, how do dams affect marine life, how dams affect rivers, how do dams affect fish migration

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