The number of juvenile Chinook salmon in the Hanford Reach has increased dramatically since changes were made to how water was released from the dam above the Reach, according to a Pacific Northwest National Laboratory study released today.
In recent years, more than 52 million juvenile salmon have been produced annually in the 50 mile section of the Columbia River between Mattawa and Richland. That's more than triple the annual average of 14 million juvenile salmon before a 1988 agreement was signed.
That agreement and a later one regulated when and how much water should be released from Priest Rapids Dam above the Hanford Reach. Both have helped make sure that eggs and young salmon remain under water.
Now the Hanford Reach has one of the most productive populations of fall Chinook salmon anywhere in the Northwest, said Ryan Harnish, a fish ecologist at the Department of Energy's national laboratory in Richland. He was the lead author on a paper published today in the Canadian Journal of Fisheries and Aquatic Sciences.
The Hanford Reach is the one of the longest free-flowing sections of the Columbia River available to salmon, and the upriver bright fall Chinook salmon that spawn there are prized for their size and quality.
Harnish and his team looked at juvenile Chinook populations in the Reach starting in the mid-1970s when several times the water level dropped so low that eggs or newly hatched fish did not stay immersed in water.
The huge losses of juvenile fish that resulted led to the 1988 Vernita Bar Settlement Agreement. It required water to be managed to protect eggs and newly hatched fish as water was held back or released from Priest Rapids Dam for flood control and production of electricity.
The agreement regulated how water was released from the dam when adult salmon were burying eggs in gravely areas in late October and November. Changes were needed to ensure that eggs laid along the margins of water channels were not in places so high that they would be uncovered when water levels dropped during the winter.
The agreement also required minimum flows as alevins -- newly hatched fish with yolk sacks still attached -- emerged in December or January. Eggs can be viable after several days without water. But alevins, which have gills, can only survive one to 10 hours if their nests are exposed to air, Harnish said.
An additional agreement in 2004, the Hanford Reach Fall Chinook Protection Agreement, added more requirements to protect juvenile salmon as they grow to an inch or two long and begin to swim out of the gravel, typically in March or April.
It limited the fluctuations in releases from the dam to make sure that the river did not drop too low, leaving small fish in shallow water near the shorelines stranded or trapped in small pools of water that would heat up or dry out.
"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," Harnish said.
The study results also indicate that other places might be able to duplicate the high survival rate of salmon from eggs to small fish in the Hanford Reach by better regulation of water flow.
Operations of Priest Rapids Dam have been altered dramatically, said Russell Langshaw, a co-author of the paper and a fisheries scientist at Grant County Public Utility District, in a statement. But the PUD has been able to protect fish and meet electric demands, working in cooperation with other operators on the Columbia River, he said.
The Priest River Dam may be doing a better job of ensuring salmon production, according to PNNL. Dam operations maintain minimum water flows that are more than twice as high as historic levels during winter, which may keep young fish in water more consistently.
In addition to Harnish and Langshaw, other authors of the paper were Geoff McMichael of PNNL, Todd Pearsons of the Grant PUD and Rishi Sharma, formerly of the Columbia River Treaty Inter-Tribal Fish Commission.
-- Annette Cary: 582-1533; firstname.lastname@example.org; Twitter: @HanfordNews