After snatching and eating almost 9,000 spring
chinook salmon and steelhead through May 31, the number of pinnipeds lurking at
Bonneville Dam has dropped to just one, a California sea lion. Steller sea
lions were completely absent by the end of May.
Sea lions at Bonneville this year ate more
than twice what they’ve averaged over the past ten years. Of the estimated
8,986 fish, California sea lions (CSL) ate 71 percent of the adult salmonids –
both spring chinook salmon and steelhead – while Steller sea lions (SSL), those
found most commonly along the Oregon and Washington coastlines, consumed 29
Estimated consumption of chinook salmon by CSL
was 6,267 fish and by SSL was 2,459.
However, biologists estimate that as many as
3,300 sea lions had resided in the Columbia River from Astoria to Bonneville
Dam this spring and could be taking as much as 20 percent of the entire spring
chinook salmon run in the river.
Together, the two species residing at
Bonneville consumed an estimated 5.5 percent of adult salmonids migrating
through the dam’s fish ladder, according to the sixth and last pinniped status
report by the U.S. Army Corps of Engineers for the 2016 monitoring season. The
report covers the period January 1 to May 31 and includes observed sea lions,
observed catch and an expanded estimate of sea lion catch that includes nights
and weekends when direct observations were not possible.
The report, “Status Report – Pinniped
Predation and Deterrent Activities at Bonneville Dam,” by Patricia L. Madson
and Bjorn van der Leeuw, both of the Corps, can be found at http://www.nwd-wc.usace.army.mil/tmt/documents/fish/2016/160415_Bonneville_pinniped_update.pdf
The decline in the number of sea lions at the
dam has been dramatic, but is normal this time of year. In the last two weeks
of May, the number of CSLs declined from 37 in mid-May to just 1 at the end of
the month. SSLs were gone by the end of the month.
The first CSL was observed on February 26. The
daily average for CSLs was 4 in March, 22 in April, and 31 in May, according to
the sixth report. The maximum number of CSLs observed on a single day at the
dam was 66 on May 4. The Corps documented 131 uniquely branded individual CSLs
through May 31. Of these, 89 have been seen in multiple years and 42 were newly
SSLs were present when observations began
January 4. The daily average for SSLs was 13
in January, 5 in February, 14 in March, 40 in
April, and 21 in May. The maximum number of
SSLs observed on a single day at the dam were
54 on May 4. The Corps documented 39 unique individual SSLs this season. Of
these, 36 were observed in previous years and three were newly identified.
The maximum number of pinnipeds (CSLs and SSLs
combined) on a single day was 120 on May 4, higher than the previous record of
116 on April 22, 2015.
Observed catches by the marine mammals was
less than half of what the Corps estimates the actual (expanded) catches
(nights and weekends added) to be. Of course, catches declined significantly as
the sea lions departed the dam in late May. Observed catches of adult salmonids
through May 31 was 4,196 fish, including 4,094 spring chinook and 102
Some 1,150 chinook were taken by SSLs and
2,944 by CSLs. SSLs took 43 steelhead
and CSLs took 59.
SSLs took more white sturgeon than CSLs with
26, while CSLs were observed to take just 3. The expanded number of sturgeon
taken was a total of 86. However, predation on sturgeon was far below the
10-year average. No sturgeon catches were observed the last two weeks of May.
The difficulty of accurately observing and
identifying catches is highlighted by the number of unknown catches. Those
total 256: SSLs took 111 and CSLs took 145 unknown species.
SSLs took 5 smolts and CSLs took 10. Shad
numbered 8 for SSLs and 41 for CSLs.
There were 231 lamprey catches, 191 of those
by CSLs and 40 by SSLs. The majority of lamprey take occurred at powerhouse 2,
followed by powerhouse 1, and then at the spillway.
SSLs and CSLs took 1 pikeminnow each and SSLs
took 23 and CSLs took 14 other types of fish.
Overall, for all fish observed to have been
taken, SSLs took 1,407 and CSLs took 3,408 for a total of 4,608 fish observed
to have been taken by the pinnipeds.
Bonneville Dam is not the only dam with sea
lions. Up to three were observed at The Dalles Dam tailrace feeding on
salmonids. One was a branded sea lion and was last seen at The Dalles Dam May
4, but sighted afterwards in the Bonneville Dam tailrace. One branded CSL was
observed in the Bonneville pool and has been seen there in multiple years.
To discourage sea lion presence and predation,
the Columbia River Inter-Tribal Fish Commission used boat-based hazing,
beginning March 7. CRITFC hazed Mondays, Thursdays, and Fridays, but that ceased
Dam-based hazing by the U.S. Department of
Agriculture began March 8. USDA hazed seven days a week in 8-hour shifts, but
that ceased May 31.
Sea lion exclusion devices (SLEDs) were
deployed at powerhouse 2 on October 26, 2015 and the remaining SLEDS were
installed by March 5, 2016. Specifically, the SLEDS at powerhouse 1 were
installed on March 1, 2016, the report said.
After several SSLs were seen climbing over the
floating orifice gates (FOGs) at powerhouse 2 and entering the fishway, according
to the report wood panels were placed on top of the FOGs to prevent this
behavior from recurring. To date there have been no additional reports of sea
lions accessing the fishway channel via the FOGs.
Pinniped management activities by the states
of Oregon and Washington were ended May 24 at Bonneville Dam for 2016. Some 59
CSLs were removed in 2016 under the section 120 permit. Fifty CSLs were branded
at Bonneville Dam in 2016. In May, 16 CSLs were trapped and euthanized.
Additional information about these activities
can be found at Oregon Department of Fish &
Wildlife’s California sea lion management
Also see, CBB, May 13, 2016, “States Kill 47
California Sea Lions At Bonneville Dam During April, 14 Added To Watch List,” http://www.cbbulletin.com/436715.aspx
Sea lions are protected under the Marine
Mammal Protection Act. However, the states are able to trap and euthanize
California sea lions under a section 120 permit under the MMPA. The latest
permit expires June 30 and NOAA Fisheries is currently mulling over renewing
that permit for five more years. The states applied January 27, 2015, to NOAA
for an extension of their previous Section 120 permit.
See CBB, June 2, 2016, “Sea Lion Task Force
Meets To Advise NOAA Fisheries On Killing Sea Lions At Bonneville Dam,” http://www.cbbulletin.com/436829.aspx
--CBB, April 22, 2016, “As Spring Chinook
Passage Picks Up At Bonneville Dam, So Do Sea Lion Numbers, Salmon Mortality,” http://www.cbbulletin.com/436547.aspx
--CBB, April 1, 2016, “Sea Lions Back At
Bonneville Dam For Spring Salmonid Return; States Apply To Extend Lethal
-- CBB, June 19, 2015, “Final 2015 Sea Lion
Predation Report: 8,474 Salmonids Taken Below Bonneville, Twice 10-Year
-- CBB, May 29, 2015, “Oregon City Saturday
Event Intended To Show Support For New Sea Lion Management Legislation,” http://www.cbbulletin.com/434130.aspx
--CBB, May 15, 2015, “Pinniped Monitoring At
Bonneville Dam This Year Showing Record Numbers Of Sea Lions, Salmon
--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