How Dams Affect Salmon Migration Essay, Research Paper
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 ocean due to their extended exposure to predators, stress, disease, and other conditions created by dams.The third effect that the slowing of the river has on salmon is that the flow velocity is so slow that the young salmon are unable to reach the sea in time for their change from fresh to salt water fish. The migration that normally takes one week, now takes six. The salmon are forced to live in the fresh water even after they have undergone their physiological changes that help them survive in the e fresh water, and then later in salt water. This change effects there color and aids them in hiding from predators. This means that the salmon are stuck in fresh water without the protective camouflage to fit the rivers, but instead have the coloring to hide in the ocean.
As of yet the only significant action taken in giving salmon access to their breeding grounds was the building of adult salmon ladders, arificial waterfall-like steps going up a dam, and small bypasses in the dams. These has succeeded in helping only a small number of adults to return to their birthplaces to spawn.
Because this is a human made problem, and because we do have control over the river due to the dams like Bonneville, this problem can be easily solved. We need to create a natural flow to the river by letting the dams “draw down.” If we draw down the reservoirs we would cool down the river and steams, and create a current that would push theletting the dams “draw down” salmon toward the ocean. By speeding up the process of migrating to the sea, the salmon would have less time to be eaten by predators, and the whole process would be much safer. Another facet of helping the salmon over the dams would be to “spill” the water over the dams and allow the salmon over each dam without having to maneuver through the dams harmful turbines.
More than fifteen percent of migrating smolt face death at each dam along the Columbia river. Many of these deaths are caused by turbines. In 1960, the cumulative mortality rate due to turbines at all the main-stream dams was estimated to reach seventy percent. This outrageous figure forced the development of ways to prevent these deaths. The National Marine Fisheries Service began effforts to curb smolt mortality in turbines in 1970. Their research was directed towards developing subermisible travelling screens (STS). The duty of STS is to divert fish entering the powerhouse away from turbines. They are placed in the upper portion of the intake area to stop the fish from going any further into the turbine intakes. The fish are then directed upward to the gatewell to the the central bypass system. The effectiveness of the STS was tested at Harbor Dam. Marked fish were released into turbine intakes from hoses connected to stock tanks on the powerhouse deck. Diverted fish were recorved from the gatewells and counted. The number of fish released was compared to the number recovered. Results showed that sixty to seventy percent of salmon were successfully guided from turbine intakes.
Bypass entrance should provide smooth transition to the screens. The screens should then direct fish into areas with a low concentration of predators. However, predation often occurrs in the bypass itself. The concentration of jeuvenile fish is an attractive feast for hungary predators. Par, the stage of salmon development before smolt, have underdeveloped float bladders making them less boyant. As a result of this they travel at lower verticle depths slipping underneath turbine intake screens. Effectivness at each dam varies but they all run into the same basic problems. Debris gets stuck in the thrashbacks and screens. In small mesh screens, algae often causes clogging. Damage often happens when dead trees and large objects bang into equipment. To increase the lifespan of the mechanical equipment, guards are installed. The screens also need protection from ice in the colder months.
It seems that many environmentalists would prefer the total elimination of dams on the Columbia River and those surrounding it, while others aren’t willing to give up the cheap hydroelectric power supplied by the dams. That makes the plight of native salmon into a controversy, and one that can only be solved, though probably only partially, by what those who care for the environment have been forced to do for decades, compromising. It appears to me that STS, bypasses, and all the devices used to help smolt and par past turbines won’t help much, since the true reason dams have killed so many salmon is the reduction of current. I took up flyfishing for trout a few years ago, and I have learned that trout, like salmon, need low temperatures and clean, oxygenated water to survive, and prefer fast moving water. The salmon need cold water, since warmer water can’t hold as much oxygen, fast currents to escape predators and migrate to the ocean in the time they are adapted to, and no concrete obstacles, or at least a way past them. Slow moving water gets heated up, altering the natural environment as well as forcing young salmon to spend more time in this unnaturally warm habitat.
Reversing the effects of dams on salmon populations is in all reality impossible. We have already caused the extinction of several stocks and placed others on the endangered species list. The question we are now facing is, “Are the dams and salmon really able to exist on the same river?” Based on our research the answer is no. Dams themselves have destroyed our salmon runs. Enhancement measures seem to be having little effect. In some cases, enhancement measures are actually harming the fish. Drawdown is, to me, the only practical and effective way of allowing juvenile salmon down the rivers, while also virtually unaffecting power supplies, agriculture, or other human requirements of the rivers. Also, drawdown will only occur when smolt are migrating downstream, since adult salmon don’t need it going upriver and nearly all of them die after spawning.
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