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Sea Lions Spending Longer Periods At Bonneville Dam;
Warm Ocean Conditions To Blame?

by Staff
Columbia Basin Bulletin, October 14, 2016

Sea Lion eats a fish.  If you don't eat you die. Sea lions have been seen at Bonneville Dam as recently as this week, long after the U.S. Army Corps of Engineers stopped its annual tracking of the predators at the dam at the end of May.

In the past five years, Steller and California sea lions in growing numbers have stalked spring chinook salmon, steelhead and sturgeon at the base of the dam beginning in January when small numbers of Steller sea lions show up. The Corps tracks the pinnipeds at the dam from March through May. By the end of May, most of the sea lions are generally gone.

In fact, the Corps reported in May 31, 2016 (its last report of the year) that just one of each type of sea lion was reported at the dam. However, at one time this spring as many as 120 Steller and California sea lions combined were at the dam, higher than the previous record of 116 in 2015.

"Now, the sea lions are hanging out for seven to eight months, whereas at one time they were here just in the spring for a few months," Robert Anderson, a pinniped expert from NOAA Fisheries in Portland, told the Northwest Power and Conservation Council's Fish and Wildlife Committee Tuesday in Portland.

He said there has been an explosive growth in the numbers of sea lions in the Columbia River over the past four years and it's likely due to changing ocean conditions.

At one time it was common for 100 to 300 of the animals to feed in the Columbia from the river's mouth to Bonneville Dam, but this year 3,864 sea lions were observed in Astoria's East End Mooring Basin, although only a fraction of those travel the 140 miles to the dam. Last year, about 2,400 sea lions were in Astoria and in 2014 the number was under 1,500, so it is a growing population.

Still, he said, as many as 40 sea lions were observed at Bonneville in August, presumably following the fall run of chinook salmon. Some 46 sea lions were observed at Bonneville September 15 and about 40 have been observed this week, according to an October 4, 2016 Council memorandum and update on unusual ocean conditions and sea lion presence and predation.

Although a definite connection has yet to be made with the number of sea lions and the number of salmon they take, NOAA Fisheries told the Council at its July meeting in Olympia that as much as 45 percent of adult salmon tagged in the Columbia estuary disappear before they make it all the way to Bonneville Dam.

"Pinnipeds are probably the primary cause of this mortality, but there are possible other causes," the lead researcher, Dr. Michelle Rub, reported to the Council in July. Those other causes include fish turning into creeks in the lower Columbia to spawn, fish deaths from disease or injury, or even learned behavior. But none of these is as strong a cause as predation by marine mammals, Rub said.

(Also see, As Many As 45 Percent Of Tagged Spring Chinook In Estuary Disappear Before Reaching Bonneville Dam by Staff, Columbia Basin Bulletin, 7/22/16).

Lethal removal of California sea lions at Bonneville Dam has been one way to reduce impacts on imperiled salmon and steelhead. NOAA Fisheries in July re-authorized the states of Oregon, Washington and Idaho to continue lethal removal of the sea lions that prey on the fish at Bonneville Dam.

In 2016, California and Steller sea lions at the dam snatched and ate 8,986 spring chinook salmon and steelhead through May 31, almost twice the 10-year average, or nearly 3 percent of returning adult fish. An estimated 25 to 35 percent of the fish consumed are listed under the Endangered Species Act.

Of the estimated 8,986 fish, California sea lions ate 71 percent of the adult salmonids -- both spring chinook salmon and steelhead -- while Steller sea lions, those found most commonly along the Oregon and Washington coastlines, consumed 29 percent.

(See NOAA Re-Authorizes States To Lethally Remove Salmon-Eating California Sea Lions At Bonneville Dam by Staff, Columbia Basin Bulletin, 7/15/16)

Much of the pinniped problem in the river begins with a warming ocean. As ocean temperatures have warmed, many species of algae, fish and animals have moved north. Last year, due to extremely warm ocean conditions, researchers found some of the highest concentrations of domoic acid (produced by a natural, but toxic algae) ever observed off the west coast, the October Council memorandum said. The toxin spread throughout the food web, from shellfish to sea lions.

(See Study Connects Massive West Coast Toxic Algal Bloom In 2015 To Unusually Warm Ocean Conditions by Staff, Columbia Basin Bulletin, 10/7/16)

In addition, humpback whales were seen in August and September this year in the Columbia River estuary as far upstream as the east side of the Astoria-Megler bridge.

"Experts suggest that ocean conditions could be driving many sea animals toward shore looking for food," the memorandum says.

Brian Burke, NOAA Fisheries' Northwest Fisheries Science Center, told the Fish and Wildlife Committee that the cause of the ocean warming was an unusually high pressure formed over the north Pacific Ocean in 2013 and 2014, and a warm area called the Blob formed in spring 2014, driven by the high atmospheric pressure and higher than normal sea surface temperatures.

(Also see Study: The Warm-Water ‘Blob,' Combined With El Nino, Depressed Marine Productivity Off West Coast by Staff, Columbia Basin Bulletin, 6/15/16)

Then along came El Nino, he said. Although the stronger than normal El Nino has dissipated (he said its over) and a neutral La Nina has taken its place, the Blob was present in the Gulf of Alaska in September 2016, according to Burke.

The warming weather, river and ocean conditions have had a number of impacts on various species causing "an unusual ecology." For example, all species of juvenile salmon are outmigrating from the Columbia River and its tributaries an average of two weeks earlier, he said.

And, "ocean survival is highly correlated with total survival," Burke said. "It's clear that mortality is occurring in the ocean."

In the ocean, high-fat content fish like sardines and anchovies are moving northward. While they could be providing a good source of food for salmon, they could also be drawing pinnipeds north.

The warming of the ocean by 1 to 3 degrees is enough to cause ecological effects, Anderson said. The change in temperature is an advantage to California and Steller sea lions; they are more efficient in warmer water. If the ocean was colder, they might not migrate as far.

As for California sea lions that are found from the Channel Islands off California up to the Gulf of Alaska, only the males migrate, he said. Once they leave the Columbia River, they return to their home grounds to mate in July and August. (One California sea lion was tracked from California, to Bonneville Dam, back to California, to the Columbia River mouth and into Puget Sound, all from February 1 to May 25, 2007.)

However, as the rich food supplies have move northward, females must hunt at greater distances from their pups and over the last four years there have been a large number of pup deaths due to what looks like abandonment, Anderson said.

The 2014 population of California sea lions was estimated at 296,750 with an annual growth rate of 5 percent each year. With the recent pup mortality, the population is likely less in 2016, but that may not impact the males seen in the Columbia River. Those sea lions are probably at their peak abundance, he said.

Steller sea lions are found from California to Alaska, as well, but their abundance is much smaller at 63,000 -- 78,000, with a growth rate of 3 percent to 5 percent each year. Breeding occurs in May. Stellers were listed as a threatened species under the federal Endangered Species Act in 1990 and delisted in 2013.

Related Sites:
Oregon City Saturday Event Intended To Show Support For New Sea Lion Management Legislation Columbia Basin Bulletin, 5/29/15

Related Pages:
NOAA's Sea Lion Task Force Discusses Lethal Removal Below Bonneville Dam by Staff, Columbia Basin Bulletin, 10/28/11
As Spring Chinook Passage Picks Up at Bonneville Dam, So Do Sea Lion Numbers, Salmon Mortality by CBB Staff, Chinook Observer, 4/22/16
Sea Lions Back At Bonneville Dam For Spring Salmonid Return by Staff, Columbia Basin Bulletin, 4/1/16
2015 Sea Lion Predation Report: 8,474 Salmonids Taken Below Bonneville, Twice 10-Year Average by Staff, Columbia Basin Bulletin, 6/19/15
Pinniped Monitoring at Bonneville Dam this Year Shows Record Number of Sea Lions,Salmon Predation by Staff, Columbia Basin Bulletin, 5/15/15
Trap Malfunction Results in Accidental Death of Two California Sea Lions at Bonneville Dam by Staff, Columbia Basin Bulletin, 5/8/15

Sea Lions Spending Longer Periods At Bonneville Dam; Warm Ocean Conditions To Blame?
Columbia Basin Bulletin, October 14, 2016

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