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Numbers Of Young Fall Chinook Migrants ‘Surprisingly High’; Corps Switches From Barges To Trucks
Posted on Friday, August 24, 2012 (PST)

The collection of mostly subyearling fall chinook salmon at the mid-Columbia River’s McNary Dam and transport of the young fish downstream aboard tanker trucks began last weekend on a daily schedule largely because the numbers of fish are “surprisingly high,” said the U.S. Corps of Engineers’ Doug Baus.

The switch from barge transportation to trucks is scheduled as the numbers of outmigrants begin to dwindle. But the pulse has remained relatively strong for this time of the year. So instead of an every-other-day schedule as originally planned, truck capacity requires that the fish be moved every day.

The transport program is intended to move fish safely downstream aboard trucks – sidestepping warm waters, predators and three downstream dams. A share of the outmigrating fish, likely half or more, pass downstream through spillways, turbines and mechanical passage with the balance being collected for transportation.

Passage of subyearling chinook at McNary last week increased, when compared to the previous week. The daily average passage index for subyearling chinook at McNary last week was nearly 50,000 per day, compared to nearly 30,000 per day the week before.

The Corps, which owns and operates the dam, had been asked last week by federal, state and tribal fish managers to forego truck transportation this year because of high water temperatures in the fish collection and holding facilities at McNary.

But the Corps declined, saying that available data indicates survival overall is better via transportation.

“We want to keep the status quo until we have data that says otherwise,” Baus said. Fears of high mortality in collection channels and holding raceways have so far proven unfounded.

“Mortalities have remained low, below 1 percent,” Baus said Wednesday. And with temperatures as of mid to late August on the decline, no problem is expected.

The truck transportation will “continue every day as long as the project managers deem it necessary,” Baus said. The original plan was to hold fish for up to 48 hours in dam raceways and load trucks for transport every 48 hours.

“We’ll be doing every day truck transport until Aug. 29,” unless conditions warrant a fallback to the every-other-day plan, Baus said.

Fishery managers such as the Nez Perce Tribe’s Dave Statler, the Washington Department of Fish and Wildlife’s Charles Morrill and the Oregon Department of Fish and Wildlife’s Rick Kruger argued that the Corps needs to re-evaluate its water temperature guidelines to determine how thermal stress might affect long-term fish survival, in addition to weighing immediate mortality at the dam.

Russ Kiefer, representing the state of Idaho, also said the Corps needs to better assess the survival benefits gained from passage improvements implemented at the dams. Passage improvements that increase in-stream survival rates could negate the need for transportation, he said.

For more information see CBB, August 17, 2012, “With Warming Water What’s Better For Juvenile Salmon: In-River Passage Or Truck Transport?”

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