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Latest Status Report Shows Sea Lion Presence At Bonneville Dam This Year Smashing Single Day Records
Posted on Friday, May 29, 2015 (PST)

The number of sea lions and the number of salmon they’ve eaten this year in the Bonneville Dam tailrace continues to rise, according to a May 22 status report by the U.S. Army Corps of Engineers.


See the report at


The highest number of California sea lions observed in one day was 70 on May 13, a new single day record, beating the 2007 record of 52. In fact, the single day records set in 2007 were beaten on nine separate days this year. The first CSL was observed February 9 this year.


Sixty-nine steller sea lions were observed April 22, also a new record for Bonneville Dam. The former record of 53 was set in 2010. The single day records from 2010 were surpassed this year on five separate days. Steller sea lions were already present when observations began January 13.


The average combined pinniped (both CSL and SSL) abundance so far in May has declined since the Corps reported in its May 12 summary a high daily average of 78 in April. So far in May, the daily average is 69 pinnipeds.


Overall in 2015, the daily average number of combined pinnipeds observed in the dam’s tailrace in January was 12, 8 in February, 22 in March and 78 in April. The highest number observed for both pinniped species combined was 116 on April 22, a new record for Bonneville. The previous record was 71 per day set in 2010. The single day record from 2010 was surpassed on 15 separate days in 2015.


Given the number of sea lions present at the dam and the number of adult spring chinook salmon passing the dam (as of May 25 that number was 203,368), it’s not surprising that the  sea lions are taking record numbers of fish.


California sea lions eat more chinook salmon than do the steller sea lions, so far gobbling up 5,496 of the fish (expanded predation estimates). Steller sea lions have taken 1,662 chinook, for a combined take by both CSL and SSL of 7,158 salmon.


CSLs took fewer steelhead (44), while SSLs took 133, for a combined take of 177 steelhead, bringing the combined total of salmon and steelhead to 7,335 fish (expanded estimate).


That’s a considerable increase in two weeks from the Corps report May 12, when the combined expanded total take of both salmon and steelhead was 5,879 fish.


Of the observed catches, California sea lions took 4,060 chinook salmon (nearly double the May 12 observed take) and 29 steelhead, while steller sea lions took 1,171 chinook and 90 steelhead (no increase for steelhead).


According to the Corps report, it has documented 185 branded CSL in the tailrace this year. Of these, 24 were brands seen in previous years, 30 were brands that had not previously been observed at Bonneville, and 131 were CSL that were trapped and branded at Bonneville this field season.


In addition, the Corps documented 53 unique individual SSL in the tailrace this year. Of these, 33 were repeat individuals and 20 were previously unidentified and may be new to Bonneville. Of the 33 repeat SSL, 15 were branded.


Pinnipeds were also observed to take 23 white sturgeon (favored more by SSLs than CSLs), 45 Pacific lamprey (nearly doubling the observed take of lamprey reported May 12), 19 American shad and 475 other or unknown species. The total observed take is 5,912 fish of all species.


The Corps and other agencies and tribes are taking measures to reduce sea lion predation with sea lion exclusion devices installed at fishway entrances and some powerhouses, as well as boat-based harassment by the Columbia River Inter-Tribal Fish Commission that began March 6 and ended May 14. Dam-based harassment that began on March 18 by the U.S. Department of Agriculture is conducted seven days a week and will continue through May.


Other management activities by the Oregon and Washington fish and wildlife departments through May 22 have permanently removed 32 CSL, euthanized 30 and two are being transferred to the Queens Zoo in New York.


A total of 131 CSL have been trapped, branded and released in 2015.


While efforts to manage sea lions in the dam’s tailrace continue, the efforts have not been without mishap. Two California sea lions died accidentally in a trap when they were crushed by a much larger sea lion in the crowded trap during the week of April 27 and one Steller sea lion died when it was accidentally caught May 4 between two traps and drowned.


For background, see:


--CBB, May 15, 2015, “Pinniped  Monitoring At Bonneville Dam This Year Showing Record Numbers Of Sea Lions, Salmon Predation,”


--CBB, May 8, 2015, “Trap Malfunction Results in Accidental Death of Two California Sea Lions At Bonneville Dam,”


--CBB, April 17, 2015, “As Spring Chinook Return Gathers Steam, Sea Lion Numbers In Bonneville Dam Tailrace Above Average,”


-- CBB, April 10, 2015, “Gillnetters Fall Short Of Harvest Target in Tuesday Fishery; Heavy Sea Lion Presence Cited,”


-- CBB, March 13, 2013, “Sea Lions Showing Large Presence in Lower Columbia; Smelt First, Then Come Spring Chinook,”


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