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River Operations In Review: 2018 Pacific Lamprey Return Below 2017, But Far Above Normal
Posted on Friday, January 11, 2019 (PST)

Although less than half the 2017 return, the 2018 migration of Pacific lamprey into the Columbia River and up through Bonneville Dam was more than three times the 20-year mean.

 

The mean return over Bonneville the past 20 years (1999 to 2018) is 38,339 lamprey. However, the number of lamprey returning to the river began to spike in 2014, reaching a total escapement (returning and potentially spawning fish) to the dam of nearly 50,000 lamprey. Returns of the lamprey continued to rise, reaching a high of 290,468 in 2017, before dropping to 131,765 last year.

 

“2017 was a banner year and 2018 was a good year,” said Dave Swank of the U.S. Fish and Wildlife Service. “I hope the new normal is not just a spike in numbers.”

 

The low point over 20 years was 2010 when just a little more than 5,000 lamprey passed Bonneville. Most of the lamprey that pass the dam do so between mid-May and the first of September.

 

Swank spoke at the interagency Technical Management Team’s Year End Review last month. TMT is made up of fisheries and hydro/reservoir managers from state, federal and tribal agencies. Every December the group looks back at actions taken during spring and summer in managing Columbia and Snake river federal hydro/fish operations.

 

Swank’s presentation was among nine reviewed in the day-long session (see http://pweb.crohms.org/tmt/agendas/2018/1219_Swank_Pacific_Lamprey_Returns_to_the_Columbia_River.pdf).

 

Still, there is a discrepancy between the numbers of lamprey passing Bonneville and the much smaller numbers passing Columbia River dams upstream. The count at The Dalles Dam in 2017 was about 25,000 fish and the numbers decline the further upstream. About 22,000 lamprey swam through the John Day Dam and few (less than 1,000) made it to McNary Dam.

 

Swank conjectured that the discrepancy is due to some lamprey spawning in the mainstem Columbia River or they move into tributaries to spawn, although that doesn’t explain the size of this drop, he said.

 

For lamprey, “it takes quite some time and energy to move through the fish ladders,” he said.

 

Still, some lamprey are able to find their way into the Snake River with about 1,400 lamprey crossing Ice Harbor Dam in 2017 and about 1,000 passing the dam in 2018. Ice Harbor is the downstream of the four lower Snake River dams. Most lamprey cross the dam between early July and early September.

 

Moving upstream, a little more than 400 crossed Lower Monumental Dam in 2017 and a few more crossed in 2018.

 

Inexplicably, more lamprey crossed the next upstream dam (Little Goose) in 2017 than had crossed Lower Monumental. That dropped precipitously in 2018 to less than 50 lamprey.

 

About 375 lamprey passed Lower Granite Dam in 2017. The number dropped to about 175 in 2018.

 

On the Willamette River about 125 lamprey were counted at the Leaburg Dam in 2017, a spike after two years of about 30 fish. Numbers at the dam since 1971 have fluctuated year to year, with the lowest year in 1971 of just 5 lamprey and the highest return was in 2003 when about 240 crossed the dam.

 

The count at Winchester Dam on the North Umpqua River in 2017 was under 1,000 lamprey. Returns of lamprey have been at that level or fewer since the late 1980s, according to Swank’s presentation. The best year was in 1966 when the return was about 47,000 lamprey.

 

Some ways to increase the efficiency of lamprey passage include reducing entrance velocities to fish ladders and modifications to fishway structures, like at one already installed at Ice Harbor Dam, Swank said. In addition, a wetted wall that help lamprey pass was installed recently at Bonneville Dam.

 

Also see:

 

-- CBB, July 13, 2018, “Council Fish/Wildlife Committee Discusses Tribal Plans To Restore Pacific Lamprey To Historic Range,” http://www.cbbulletin.com/441107.aspx

 

-- CBB, June 15, 2018, “Pacific Lamprey Return To Umatilla River In Record Numbers; From Functionally Extinct To Over 2,600,” http://www.cbbulletin.com/440946.aspx

 

--CBB, June 1, 2018, “Science Panel Reviews Tribes’ Master Plan For Recovering Pacific Lamprey In Columbia River Basin,” http://www.cbbulletin.com/440843.aspx

 

--CBB, February 17, 2017, “Study Looks At Genetics, Migration, Behavior Of Pacific Lamprey In Willamette River,” http://www.cbbulletin.com/438353.aspx

 

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