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Pinniped Report: Sea Lions Leave Bonneville Dam with
Likely High Salmon Predation Rate in Their Wake

by Staff
Columbia Basin Bulletin, June 23, 2017

Graphic: Sea Lion consumption of salmon has changed recently with Stellar Sea Lions now stay thoughout much of the year. After a month with the number of sea lions hanging out at Bonneville Dam to snack on salmon, steelhead and other available fish exceeding the 10-year average, the number fell to just one, according to a June 7 report.

Most of the Steller sea lions left by May 27 and by the end of the reporting period, May 13 to June 2, there were none remaining at the dam. The bulk of the California sea lions left by May 30, but one remains, the report says. During the period there were an average of 37.5 sea lions in the dam's tailrace per day. Most were Steller sea lions, averaging 24.3. California sea lions averaged 13.1 over the same period. No seals were present at the dam this year.

While at the dam, the sea lions' relative impact on the small run of spring chinook and lagging numbers of steelhead was likely large.

The U.S. Corps of Engineer's June 7 report (Bi-Weekly Update: Pinniped Abundance and Salmon Predation at Bonneville Lock and Dam), the fourth and final report of the year, says about 1,837 adult salmonids were consumed by the sea lions May 13 to June 2, far higher than the 10-year average for the same period of 437 adult salmonids.

The report was prepared by Kyle Tidwell, Thomas Van Hevelingen, Lindsay Magill, and Bjorn van der Leeuw, all of the Corps' Fisheries Field Unit.

Over the entire reporting period (January 1 - June 2), sea lions ate 4,993 adult salmonids. Some 82 percent of those were spring chinook salmon. Six sturgeon were eaten, according to observers, and lamprey and other non-salmonids accounted for less than 5 percent of the predation.

"A review of the combined salmonid passage counts for the pinniped sampling season shows that the runs were delayed relative to previous years and smaller than the long term average," the report says. "As such, the duration of pinniped presence and levels of fish predation were protracted relative to the 10 year average. The reduced salmonid runs and persistently high numbers of pinnipeds in the latter part of the season suggests that the total impact by pinnipeds on this year's salmonid run may be large."

The final predation numbers are being processed and will be available at a later date.

What's clear this year is that the spring chinook run was far lower than average. The U.S. v Oregon Technical Advisory Committee initially predicted a run of 160,400 fish. That was revised down by TAC to 118,000 fish arriving at the mouth of the Columbia River and 110,000 fish over Bonneville Dam. The spring chinook run over the dam transitioned to the summer chinook run June 15.

By June 15, some 107,524 adult spring chinook had passed Bonneville.

Observers documented 15 Steller and 88 California sea lions as uniquely identifiable individuals. All uniquely identifiable pinnipeds have been documented near Bonneville tailraces project in previous years or were recently branded at Bonneville.

No sea lions have been observed at the Dalles Dam or above the Bonneville Dam since May 18.

Monitoring at the dam began January 10 and concluded June 2.

Deterrence and trapping activities are fully operational with all state, tribal, and federal entities working together to monitor this year's pinniped-fish interactions.

Some 24 of the California sea lions that have been identified, marked and trapped, have been euthanized this year. Two were euthanized the week of May 15, eight the week of May 8, six the week of May 1, seven the week of April 24 and one the week of April 17. Trapping reports are at

In April, two members of the Northwest's congressional delegation -- U.S. Reps. Jaime Herrera Beutler (R-WA) and Kurt Schrader (D-OR) -- introduced the Endangered Salmon and Fisheries Predation Act in Congress to expedite the removal of sea lions at Bonneville Dam that would make it easier for tribes and states to obtain permits to remove sea lions from the Bonneville Dam tailrace. That bill is still in committee.

Related Pages:
Spring Chinook Run Forecast Stays At 118,000 As Harvest Managers Move Into Summer Chinook Season by Staff, Columbia Basin Bulletin 6/9/17
Sea Lion Numbers At Bonneville Increase, Salmon Predation Below Average So Far by Staff, Columbia Basin Bulletin 5/12/17
Slow Start This Year But Sea Lions Back At Bonneville Dam For Spring Chinook Feasting by Staff, Columbia Basin Bulletin 4/28/17
Bill Introduced In Congress Again To Expedite Removal Of Sea Lions From Bonneville Dam Tailrace by Staff, Columbia Basin Bulletin 4/14/17
Corps Report: Sea Lions In Bonneville Dam Tailrace In 2016 Consumed 4.5 Percent Of Spring Chinook by Staff, Columbia Basin Bulletin 3/10/17
Final 2016 Pinniped Report: Sea Lion Salmon Take Astoria To Bonneville Dam Could Be 20 Percent Of Run by Staff, Columbia Basin Bulletin 6/17/16
Final 2015 Sea Lion Predation Report: 8,474 Salmonids Taken Below Bonneville, Twice 10-Year Average by Staff, Columbia Basin Bulletin 6/19/15

Related Pages:
Bill to Expedite Sea Lion Removal Clears House Natural Resources Committee by Staff, Columbia Basin Bulletin, 8/1/17
Congress Seeks to Weaken the Marine Mammal Protection Act by Maya L. Kapoor, High Country News, 7/28/17
House Natural Resources Committee Passes Bill to Expedite Sea Lion Removal by CBB Staff, Chinook Observer, 10/14/16
Predatory Sea Lions Are Detrimental to Columbia River Fish Runs by Gerry Lewis & Paul Ward, NW Fishletter, 5/1/17
Bill Would Streamline Process to Kill Sea Lions Near Bonneville Dam by Brian Brennan, KGW8, 4/4/18

Pinniped Report: Sea Lions Leave Bonneville Dam with Likely High Salmon Predation Rate in Their Wake
Columbia Basin Bulletin, June 23, 2017

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