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Bonneville Dam Flows Configured To Limit Descaling Of Central Idaho’s ESA-Listed Sockeye
Posted on Friday, May 25, 2012 (PST)

A greater percent of Columbia River flows this week through Bonneville Dam have once again been steered southward, this time in anticipation of the arrival of a large portion of the ocean-bound juvenile sockeye salmon that originated in central Idaho’s Stanley basin.

 

Last week a Wednesday through Monday operation was implemented by the U.S. Army Corps of Engineers that drew more of the spring flows through Bonneville’s Powerhouse 1, which is situated near the Oregon shore, as opposed to Powerhouse 2 near the Washington shore. In between is the dam’s spillway, the third option for passing water and fish downstream.

 

Last week’s switch was made in an attempt to draw more fish to Powerhouse 1 and away from Powerhouse 2 where severe descaling and mortality of migrating sockeye had been witnessed. Increased velocities and resulting turbulence at Powerhouse 2’s gatewells – the entrance to the turbines and/or a bypass system intended to shepherd fish safely downstream – has been blamed for the sockeye injuries.

 

The sockeye descaling rate had been as high as nearly 24 percent while other fish are less affected. Yearling chinook had descaling rates of less than 6 percent over the past week, and usually considerably less.

 

Meanwhile, the operation implemented May 16 through this past Monday saw descaling of sockeye dip to as low as 5 percent but then slowly begin to rise by the end of the weekend. The total was 22.7 percent Sunday and 24.1 percent Monday, according to data compiled by the Fish Passage Center from fish sampling at the dam.

 

“You take your best shot,” NOAA Fisheries’ Paul Wagner said of the operation, which seemed to limit descaling and mortalities at Powerhouse 2 for most of the period. Sockeye mortalities actually dipped from a high of 9.8 percent to zero for a few days during the operational change. Mortality estimates rose to 6.9 percent Tuesday, the day the majority of the flows were again being channeled through Powerhouse 2.

 

The bulk of the sockeye passing so far have been unlisted fish originating primarily from the Okanogan River basin in northern Washington and southern British Columbia.

 

Yet to come is the majority of the sockeye from Idaho’s high country that head down the Salmon, Snake and Columbia rivers on their way to the Pacific. Those fish are mostly the product of the Snake River Sockeye Salmon Broodstock Program, which was started in the early 1990s in an attempt to head off extinction of the species. Snake River sockeye are listed as endangered under Endangered Species Act.

 

According to Dan Baker a total of about 165,000 hatchery-reared sockeye smolts were released in central Idaho on May 10. Also, an estimated 20,000 to 30,000 smolts have emerged from Redfish Lake this year, a number that is “up quite a bit” from previous years, said Baker, the manager of the Idaho Department of Fish and Game’s Eagle Hatchery. The Redfish smolts are the result of natural spawners there, where larger numbers of anadromous adults – most of which began life in the broodstock program – have spawned during the past few years.

 

Between 1991 and 1998, only 16 wild sockeye salmon returned to Idaho. All of these adults were incorporated into the captive breeding program and spawned at the Eagle Fish Hatchery.

 

Between 1999 and 2010, 3,193 hatchery-produced adult, sockeye salmon – and a few naturally produced fish most likely stemming from the program -- returned to the Sawtooth Valley. For comparison, in the 14 years from 1985 through 1998, 77 natural-origin sockeye salmon returned to Idaho.

 

From 2011-2008 the annual adult return totals were 720, 1,355, 833 and 650. Some of the fish were used to restock the hatchery program; many were allowed to spawn on their own in Redfish. Hatchery raised adult fish have also been released into the lake.

 

Given travel times charted in the past, the bulk of the Snake River sockeye smolts were expected to begin arriving at Bonneville this week, Wagner said. Sockeye in general are known to “travel as a pretty tight group,” he said, so it was suggested that the flow shift be re-implemented from Wednesday through this coming Monday in hope of accommodating most of the Snake River fish, as well as remaining Okanogan fish. NOAA Fisheries is charged with protecting salmon stocks that are ESA listed.

 

The Corps agreed to implement the operation, channeling more water through Powerhouse 1 at an “open geometry” setting. The amount of flow through the two powerhouses has effectively been flip-flopped.

 

The open geometry setting results in more water being sent through the Powerhouse 1 than under a range of flows within 1 percent of the turbine’s peak operational efficiency, which many believe is the safest for fish. Salmon managers representing the tribes, the states of Oregon and Washington and the U.S. Fish and Wildlife said last week and again this week that holding flows in that 1 percent range, and perhaps sending more water over the spillway, should be considered as a strategy for reducing Powerhouse 2 flows.

 

But Corps officials have said during recent meetings of the Technical Management Team that they believe the open geometry strategy provides relatively safe passage for fish, and that increasing spill could raise total dissolved gas to levels that could harm fish and also produce turbulence below the dam that delays upstream passage of spawning salmon.

 

No one at Wednesday’s TMT – made up of federal, state and tribal fisheries and hydro managers – objected to the Corps’ planned operation.

 

The fact that sockeye are more susceptible to descaling as a result of dam passage, and more sensitive in general, is undisputed. The reason is largely a mystery.

 

“I can’t give you a specific anatomical mechanism that leads to that susceptibility,” said Kim Hyatt, a scientist with Fisheries and Oceans Canada who has long studied sockeye behavior.

 

The species is “anatomically and neurologically more sensitive to any kind of physical abrasion” than any other salmon species, said Hyatt, who’s based at the agency’s Pacific Biological Station on Vancouver Island.

 

He said he came to that conclusion accidentally long ago when involved in a doctoral program in which he was studying foraging habits of sockeye and rainbow trout.

 

When handling young fish in the laboratory he would occasionally fumble one to the floor. The trout, once put back in water, “would sulk for a while and then get on,” Hyatt said. More often than not, the sockeye would not survive.

 

Many more studies since have come to the same conclusion.

 

“The evidence that they are more sensitive is fairly persuasive,” he said. Their eating habits could have something to do with it.

 

Sockeye are “plankton pickers,” Hyatt said, mostly eschewing some of the larger plant and animal foodstuffs favored by other salmon species. For some reason the sockeye’s relatively large scales detach more easily than those of other salmon species, he said.

 

Most of the sockeye juveniles headed for the ocean are 1-plus years and perhaps slightly smaller than yearling chinook but not greatly so.

 

“At an equivalent size they’re just a more sensitive species,” Hyatt said.

 

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