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Sea Lion Presence At Bonneville Dam Up;
Salmon Predation Exceeds Historical Average

by Staff
Columbia Basin Bulletin, June 2, 2017

Sea lions ate an estimated 2,340 adult salmonids from May 1 to 12, a number that is significantly higher than the 10-year average of 1,599 fish for the same period.

A scapegoated sea lion next to the killing machine on the Columbia River. Photo: Ninette Jones, Sea Lion Defense Brigade

The sea lion population at Bonneville Dam has climbed above the 10-year average and so has the number of salmon and steelhead the animals are preying on, according to the most recent pinniped status report released by the U.S. Army Corps of Engineers, May 18.

This is the third such report released this season. It records sea lion presence and predation at the dam from January 1 through May 12, but highlights the nearly two weeks from May 1 to 12. Monitoring at the dam began January 10 and will continue through May 31, after most of the sea lions leave for mating.

The third status report, Bi-weekly update: Pinniped abundance and salmon predation at Bonneville Lock and Dam.

While the combined numbers of sea lions – both Steller and California sea lions – at the dam through April 28 was below the 10-year average, those numbers climbed and topped the 10-year mark from May 1 to 12, the status report says.

The average number of sea lions observed at the dam per day during this period was 69.8 animals. Most of those were Steller sea lions, the typical pinniped found along the Oregon and Washington coastlines. The average daily count of Steller sea lions for the period was 50.2. The average daily count of California sea lions was 19.6. The maximum number of Steller sea lions was 63 on May 5, and for California sea lions it was 28 on May 4. No harbor seals had been observed.

The first status report recorded just 6.6 sea lions per day on average and 6.1 of those were Steller sea lions.

Over the second status report's period, April 7 to April 28, the abundance of sea lions observed at the dam averaged 26.5 Steller sea lions and 8.4 California sea lions per day, higher than the 10-year average for the period. The daily maximum count for Steller sea lions was 49 on April 26 and 22 for California sea lions on April 28.

Of the California sea lions observed in the latest report, 56 had been uniquely identified with brands while 15 of the Steller sea lions had been uniquely identified. Uniquely identified means that a sea lion has been seen at Bonneville in prior years or was recently branded by Oregon or Washington. According to the status report, the states re-initiated Steller sea lion branding this year for the first time since 2013. "These brands will inform future study of pinniped impact on salmonid stocks," the report says.

Sea lions' predation on salmon and steelhead increased during the last week of April surpassing the 10-year average, but the number of fish the sea lions ate began to decline the first week of May and has continued to decline, following a 10-year downward trend that generally ends by May 31 when sea lions leave for the mating season. By May 12, however, predation still exceeded the 10-year average.

Sea lions ate an estimated 2,340 adult salmonids from May 1 to 12, a number that is significantly higher than the 10-year average of 1,599 fish for the same period. Some 82 percent of those fish were spring chinook. Pinnipeds ate just six white sturgeon, a fish that has historically been a main part of the Steller sea lion diet. Pacific lamprey and other non-salmonids accounted for just 3 percent of predation events.

The bulk of the overall predation was by Steller sea lions, presumably a function of their increased and sustained presence at the dam compared to the number of California sea lions, the report says. In fact, during the reporting period there was twice the number of Steller sea lions than California sea lions.

Through May 12, just 33,288 spring chinook had passed the dam, far below the 10-year average. Passage has picked up, which could mean that predation by sea lions could pick up and be reported in the fourth status report. By May 30, passage of spring chinook at the dam rose to 82,313. Last year on that date 135,808 chinook had passed the dam. The 10-year average is 148,701 fish.

"The current level of salmonid predation by pinnipeds is similar to the ten year average, but the reduced salmonid run suggests that the total impact by pinnipeds on this year's salmonid run may be large," the report concludes.

To reduce predation, boat-based hazing by Columbia River Inter-Tribal Fish Commission resumed on April 24. Dam-based hazing by USDA began March 6 and continues seven days a week for 8 hour shifts during daylight hours.

Some 24 of the California sea lions that had been identified, marked and trapped, have been euthanized this year. Trapping reports are at

Some would like to see a large increase in the numbers of sea lions that are removed and euthanized. To that end, U.S. Reps. Jaime Herrera Beutler (R-WA) and Kurt Schrader (D-OR) introduced the Endangered Salmon and Fisheries Predation Act to the House of Representatives in April. The bill would make it easier for tribes and states to obtain permits to remove sea lions from the Bonneville Dam tailrace, and would allow Northwest states and tribes to potentially obtain sea lion removal permits via an expedited process.

The bill, which has been introduced twice before, is still in the House Natural Resources Committee and should be approved and moved out of committee at some point, according to Mark Walker, Public Affairs Division Director at the Northwest Power and Conservation Council.

Bill Booth, Council member from Idaho, and Tom Karier, member from Washington, were in Washington D.C. last week meeting with members and staff of the Northwest congressional delegation about this legislation, Walker said. The Council strongly supports the bill.

"The bill has been introduced in the House during previous Congresses and has gotten traction there, but it has never made any headway in the Senate," Walker said. "Both Bill and Tom encouraged the continued support in the House and for the NW Senate offices to also take a strong interest in it."

Related Sites:
Bill Introduced In Congress Again To Expedite Removal Of Sea Lions From Bonneville Dam Tailrace by Staff, Columbia Basin Bulletin 4/14/17
Slow Start This Year But Sea Lions Back At Bonneville Dam For Spring Chinook Feasting by Staff, Columbia Basin Bulletin 4/28/17
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 6/17/17
Final 2015 Sea Lion Predation Report: 8,474 Salmonids Taken Below Bonneville, Twice 10-Year Average by Staff, Columbia Basin Bulletin 6/19/17

Related Pages:
Early Action Key to Reducing Sea Lion Impacts on Salmon by Staff, Science Daily, 12/16/16

Sea Lion Presence At Bonneville Dam Up; Salmon Predation Exceeds Historical Average
Columbia Basin Bulletin, June 2, 2017

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