After a record year of devouring nearly 8,500 chinook salmon
and steelhead in the Bonneville Dam tailrace, the Steller and California sea
lion (pinnipeds) presence is on the decline, reaching a season daily average
low May 29, the last day of daylight observations.
The U.S. Army Corps of Engineers, which has reported every
two weeks since March 12 sea lion abundance and their predation on salmon and
other fish species at the dam, completed its final report of the year, June 9: see
the report at http://www.nwd-wc.usace.army.mil/tmt/documents/fish/2015/2015_0609_Bonneville_Pinniped_%20Biweekly_Report.pdf
The number of sea lions and the number of salmon they’ve
eaten this year at Bonneville Dam rose to record levels, according to the
status report. The daily averages in April rose to more than twice the ten year
daily averages in the years 2002-2014.
There was an average of 12 pinnipeds per day in January and
eight in February, and the sea lion presence per day rose from there to 22 in
March, 78 in April and 56 in May.
The highest per day count was April 22 with 116 pinnipeds in
the tailrace, a new record for Bonneville Dam. The former record was in 2010
with 71 pinnipeds. The single day record from 2010 was surpassed on 15 separate
days in 2015.
To break that down by sea lion species, the first California
sea lions arrived at the dam February 9 and the highest number was 70 on May
13, a new record for Bonneville. The former record of 52 was set in 2007. The
single day record from 2007 was exceeded this year 12 times.
Some 190 California sea lions were branded -- 28 were
branded in previous years and are returning sea lions. Another 31 were brands
on sea lions not previously observed at Bonneville and 131 were trapped and
branded at Bonneville this year.
The first Steller sea lions were observed January 13, with
the highest daily number of 69 observed on April 22. That’s a new Bonneville
record. The previous daily record was 53 Steller sea lions in 2010. The single
day record from 2010 was exceeded on five days this year.
The Corps documented 54 unique individual Steller sea lions.
33 were repeat sea lions and 21 were unidentified and may be new to the dam. Of
the 33 repeat sea lions, 15 were branded.
With so many pinnipeds in the river, predation of adult
spring chinook salmon and steelhead by the sea lions was also the highest on
record. In total, pinnipeds ate 8,474 salmonids, January 1 through May 31, a
number that far exceeds the 10-year average of 3,515 fish. The 8,474 salmonids
is an increase over the May 22 report of 7,335 salmonids.
California sea lions consumed the most, eating 6,574 spring
chinook and 47 steelhead. Steller sea lions consumed 1,720 chinook and 133
steelhead. Both are expanded numbers, which are estimates that take into
account the times when sea lions were not being observed (weekends and nights).
Pinnipeds were also observed to take 23 white sturgeon
(favored more by SSLs than CSLs), 107 Pacific lamprey, 38 American shad and 539
other or unknown species. The total observed take is 6,711 fish of all species
(this is different from the expanded estimates, which are not available in the
report for fish other than salmonids).
White sturgeon predation of 34 fish was low in 2015 compared
with the 2006-2014 average of 1,285 sturgeon.
The Corps and other agencies and tribes had taken measures
this year 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 began on March 18 by the U.S.
Department of Agriculture was conducted seven days a week and ended May 31.
Other management activities by the Oregon and Washington
fish and wildlife departments through May 31 permanently removed 32 CSL,
euthanized 30 and two were transferred to the Queens Zoo in New York.
A total of 131 CSL have been trapped, branded and released
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,” http://www.cbbulletin.com/434021.aspx.
--CBB, May 8, 2015, “Trap
Malfunction Results in Accidental Death of Two California Sea Lions At
Bonneville Dam,” http://www.cbbulletin.com/433946.aspx.
--CBB, April 17, 2015, “As
Spring Chinook Return Gathers Steam, Sea Lion Numbers In Bonneville Dam
Tailrace Above Average,” http://www.cbbulletin.com/433726.aspx.