Controlling Dam Water Levels Could Increase Number Of Salmon

By Shweta Iyer on February 25, 2014 2:19 PM EST

salmon
According to a study published in the Canadian Journal of Fisheries and Aquatic Sciences, salmon productivity is greatly affected by the flow and level of water. (Photo: Photo courtesy of Shutterstock)

According to a study published in the Canadian Journal of Fisheries and Aquatic Sciences, salmon productivity is greatly affected by the flow and level of water. The study cites the example of the Priest Rapids Dam, where the number of salmon downstream of the dam increased three-fold over a 30-year period, by adjusting water discharges.

"This is one of the most productive populations of fall Chinook salmon anywhere in the Pacific Northwest. Much of this productivity can be attributed to the way in which operations of Priest Rapids Dam have been altered over the past 30 years," said Ryan Harnish, co-author of the paper and a fish ecologist at the Department of Energy's Pacific Northwest National Laboratory, according to a press release Tuesday.

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"The timing of life stages in relation to water temperature has been studied so extensively for this population that we have a good idea of when the eggs will be hatching, when the young fish will emerge from the gravel, and when the smolts will migrate to sea," Harnish went on to say. "This allows for water flows to be planned around these life events, to minimize the risk that the eggs and the young fish below the dams will be dewatered."

Construction of dams has sometimes altered the historic river flow patterns and thus affected the spawning habitats of salmon. But a fact not well-known is that the way dams hold back and release water for flood control and production of electricity also has a negative impact on salmon breeding.  

The authors analyzed data from 1975 through 2009 about salmon downstream from the Priest Rapids Dam, in an area known as the Hanford Reach, to project how flow of water impacted salmon production. The section of the Columbia River, about 50 miles long and roughly between the communities of Mattawa and Richland, borders the Hanford Site and is one of the longest free-flowing sections of the Columbia River available to salmon. The salmon foundt here are called Chinook Salmon and are known for their size and quality.

The study estimated that in recent years 52 million juvenile salmon were produced annually in the Hanford Reach area. This was an increase of around 14 million salmon annually before the agreements took effect. "One takeaway message from our study is that the constraints agreed upon 10 and 26 years ago are still working to protect salmon in the Hanford Reach," said Harnish.

The major reason for increased productivity was due to the prohibitions enacted as part of the VBSA to prevent the dewatering of salmon nests known as redds. The team saw additional benefit from changes designed to limit stranding and entrapment of young fish, which allowed more of them to reach the pre-smolt stage, when they are big enough to migrate downstream.

Russell Langshaw, another co-author of the paper and a fisheries scientist at Grant County Public Utility District, which runs the Priest Rapids Dam and which funded the study said, "This program is an excellent example of how commitment to sound science and adaptive management can help identify the appropriate balance between resource use and protections. Operations at Priest Rapids Dam are altered dramatically to meet constraints of the HRFCPPA. We're able to provide these protections and meet load demand because of the strong commitment by all operators on the mid-Columbia to act as a coordinated system. In a time when abundance and productivity are declining for many salmon stocks, it's exciting and rewarding to contribute to increases for such an important one."

The study also reveals how dams can boost salmon production in certain ways. For instance, prior to the development of the hydroelectric system, water flow in the Columbia could drop very low in winter. These low flows along with freezing temperatures destroyed eggs and young salmon. But current dam operations have increased levels of water, than would occur naturally, thus providing young fish a habitat to survive.

 Source: Harnish, RA. McMichael, GA. et al. Effect of hydroelectric dam operations on the freshwater productivity of a Columbia River fall Chinook salmon population. Canadian Journal of Fisheries and Aquatic Sciences. 2014.

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