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ESA Winter Steelhead Impacted by Prolonged
Steller Sea Lion Presence at Bonneville Dam

by Staff
Columbia Basin Bulletin, February 1, 2019

Estimated consumption of salmonids by sea lions at Bonneville Dam  (2002-2018). Steelhead were hit hardest by steller and California sea lions at Bonneville Dam in the fall of 2017 and the spring of 2018.

Most of the predation by the pinnipeds at the dam is now by steller sea lions as their numbers have risen in both spring and fall, while the numbers of California sea lions is dropping, according to an annual pinniped predation report by the U.S. Army Corps of Engineers.

Some 7.2 percent of the steelhead run from January through May 2018 was taken by the predators and 6.8 percent of the winter steelhead run was taken November 2017 through March 2018 (pinnipeds took 11 percent of the steelhead run in 2009). Of the winter and summer runs of steelhead, steller sea lions took 6.1 percent while California sea lions took 1.1 percent.

Although the number of salmonids taken by pinnipeds during the year was lower than in 2017, the number lost is still near the 10-year average, the Corps report says.

At the request of NOAA Fisheries, the Corps began sampling during the fall and winter months (August 15-December 31, 2017) to monitor the growing steller sea lion presence at the dam in order to evaluate pinniped predation on fall- and winter-run salmonid stocks. They found that during that period, 3.1 percent of the coho run was lost to pinnipeds and 1.5 percent of the summer and winter steelhead run was lost.

The report, "Evaluation of Pinniped Predation on Adult Salmonids and Other Fish in the Bonneville Dam Tailrace, 2018," was completed January 24, by the Corps' Portland District, Fisheries Field Unit. Its authors are Kyle Tidwell, Brett Carrothers, Kristen Bayley, Lindsay Magill and Bjorn van der Leeuw. It is available here.

The 2014 Federal Columbia River Power System Biological Opinion requires the Corps to monitor the seasonal presence, abundance, and predation activities of sea lions at Bonneville Dam. Previous annual reports are at here.

Losses were to all species of salmonids. During the spring (Jan. 1 to June 2) 3 percent of all salmonids in the dam's tailwater succumbed to sea lions. That's about 3,112 fish. Breaking that down, 2.9 percent of the chinook salmon run and 0.04 percent of the lamprey run were lost, in addition to the steelhead losses.

As a comparison, sea lions took 0.4 percent of the total salmonid run in the spring of 2002 and that rose to 4.3 percent during the low-flow year of 2015 and 5.8 percent in 2016.

Of all salmonid losses to the predators during the spring (3,112), some 2,368 were consumed by steller sea lions - that's 2.3 percent of the run - and 746 salmonids by California sea lions (0.7 percent of the run).

Pacific lamprey were also hit by the sea lions, with a total of 58 consumed. Steller sea lions consumed 20 of those, while California sea lions ate 38.

Losses in the fall (Aug. 15 to Dec. 31) for all salmonids were 892 fish, 1.2 percent of salmonids at the dam. That includes 0.7 percent of the chinook salmon at the dam, as well as the losses to coho and steelhead. This was during a period when an estimated 426,162 total salmonids passed Bonneville Dam. In addition, 238 white sturgeon were taken by the sea lions, all 2 feet to 4 feet in length.

Most fall chinook salmon were taken in mid-September, while steelhead depredation was heaviest in late-August and early-December. Coho were the predominant prey from mid-October through mid-November.

However, observers during the fall period documented weekly predation estimates of as much as 27 percent for chinook, 53 percent for steelhead and 48 percent for coho relative to the number of fish passing the dam during a specific week.

"These levels of consumption are a direct result of the increasing presence of predatory SSLs at BON and the growing population of BON-habituated SSL," the report says. "Columbia River salmonids now contend with quasi-resident SSL predators that have increased in abundance and predatory impact."

The number of steller sea lions in the spring was 4.7 percent higher than last year and 4.8 percent higher than the 10-year average. The number of California sea lions dropped by 27.1 percent from last year and by 23.9 percent of the 10-year average.

"The near record low runs of ESA-listed winter and summer steelhead and small run of ESA-listed spring Chinook Salmon that passed Bonneville Dam this sampling season had to swim past high numbers of SSLs, however numbers of CSLs are slightly lower than past years," the report says. "Our estimates show that in general: CSL abundance and fish consumption are down, SSL abundance and fish consumption are up, and the total number of salmonids killed this year by both species of pinniped, although lower than previous years, is similar to the ten year average.

"We documented increasing trends in White Sturgeon predation that are of concern, and identified that ESA-listed winter steelhead are being impacted by prolonged SSL presence and predation," the report continued.

The report said that, just as Upper Willamette River winter steelhead are at risk due to pinniped predation, so too are the steelhead at Bonneville Dam.

"Fish and wildlife managers need to take action to ensure the continued existence of steelhead, and other threatened and endangered anadromous fish species. This should entail a review of the current CSL management plan, and the development of an equitable SSL management plan," the report says.

Other than the Corps' monitoring program (this report includes fall 2017 through spring 2018), the Corps collaborates with state, tribal, and federal agencies charged with managing fish and pinniped species. Since 2008, the states of Oregon, Washington, and Idaho have implemented a pinniped removal program at the dam under section 120 of the Marine Mammal Protection Act to permanently remove predatory California sea lions that are having significant negative impacts on the recovery of ESA-listed chinook salmon and steelhead stocks, the report says. The Columbia River Inter-Tribal Fish Commission also collaborates with the program with its boat-based hazing efforts, and the U.S. Department of Agriculture provides dam-based hazing.

Still, the number of pinnipeds at the dam during the fall months (August through December) has generally been on the rise with none in August and September 2011, but 10.8 and 13.2 respectively by 2017. In October 2011 some 2.4 pinnipeds were observed on average, rising to 14.8 by 2017. There was a spike in the low-flow years of 2015 and 2016 to 22.5 and 26.6. November 2011 saw 4.9 and in 2017, the number was 18.5. December 2011 saw 7, but by 2017 the average number had risen to 16.4.

During the 2017 fall period, just 3 individual California sea lions were observed at the dam, but 36 individual steller sea lions were present. This proportion of California to steller sea lions in the fall has been typical since 2011, and, in fact, the first California sea lion hadn't shown up at the dam until Nov. 2, 2017.

Some 92 California sea lions were marked and authorized for removal at the dam during the spring period: 27 were actually removed in 2018. The highest level of removal was in 2016 when 57 were removed. 2008 was the first year for removal under a MMPA Sec. 120 permit: 11 were removed.

Sea lions are protected under the federal Marine Mammal Protection Act. California sea lions in the U.S. are not listed as endangered or threatened under the federal Endangered Species Act. The most recent population estimate for the sea lions in the U.S. was 296,750 animals in 2016.

Legislation that will allow the lethal removal of more California sea lions, as well as steller sea lions, from the Columbia River was signed into law by President Trump in December. The Endangered Salmon and Fisheries Predation Act amends the existing Marine Mammal Protection Act of 1972 by giving more flexibility to remove sea lions that prey upon threatened and endangered salmon and steelhead in the Columbia River. The bill also lists white sturgeon as a protected species. Oregon, Washington, Idaho and CRITFC have said they will apply for a MMPA Sec. 120 permit to begin removing steller sea lions at Bonneville Dam.

In addition, a MMPA Sec. 120 permit was given to the Oregon Department of Fish and Wildlife last year to lethally remove up to 93 California sea lions from Willamette Falls on the Willamette River near Portland in order to protect from predation by the mammals the runs of wild winter Upper Willamette River steelhead and spring chinook. ODFW has lethally removed five California sea lions in the past two months.

Related Pages:
With New Permit, Oregon Begins Lethally Removing Sea Lions At Willamette Falls To Protect Steelhead by Staff, Columbia Basin Bulletin 1/11/19
Legislation Awaiting President's Signature Would Allow Significant Increase In Killing Of Salmon-Eat by Staff, Columbia Basin Bulletin 12/14/19
Oregon Plan To Euthanize Sea Lions At Willamette Falls Approved By NOAA Fisheries by Staff, Columbia Basin Bulletin 11/20/18
Corps Report: Pinniped Predation Consumed 4.7 Percent Of Salmonids In 2017 In Bonneville Tailwater by Staff, Columbia Basin Bulletin 3/16/18
West Coast California Sea Lion Population Has Rebounded; Meets Marine Mammal Protection Act Goal by Staff, Columbia Basin Bulletin 1/19/18
Recovery Of West Coast Marine Mammals Dramatically Increasing Consumption Of Chinook Salmon by Staff, Columbia Basin Bulletin 12/1/17

Related Pages:
Falling Prey by Eric Barker, Lewiston Tribune, 5/20/18
Hazing Sea Lions Not a Long-term Fix by Dameon Pesanti, The Dalles Chronicle, 5/11/18
Bill Would Streamline Process to Kill Sea Lions Near Bonneville Dam by Brian Brennan, KGW8, 4/4/18
'We're Losing' Sea Lion Fight by Dameon Pesanti, Spokesman-Review, 4/5/18
Sea Lions Focus of Fish Survival War by Gillian Flaccus, The Dalles Chronicle, 3/22/18

As Spring Chinook Arrive, Steller Sea Lion Presence at Bonneville Dam Breaks Single Day Record
Columbia Basin Bulletin, February 1, 2019

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