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December 12, 2018
Sea Lion Predation on Columbia River Salmon and Steelhead
Since the 1990s, concerns have grown about sea lion
Table 1. Consumption Estimates on Salmonids by
predation on Columbia River salmon and steelhead
California and Steller Sea Lions (January–May)
(salmonids). Management of these species has been
complicated by requirements to protect sea lion populations
Bonneville
Total
Percentage
under the Marine Mammal Protection Act (MMPA; 16
Salmonid
Salmonids
Salmonid
U.S.C. §§1361 et seq.) while maintaining efforts to recover
Year
Passage
Consumed
Run
salmonid populations under the Endangered Species Act
2002
284,732
1,010
0.4%
(ESA; 16 U.S.C. §§1531 et seq.). Sea lion populations have
2003
217,934
2,329
1.1%
increased since enactment of the MMPA in 1972. In the
Columbia River Basin, 13 salmonid runs now are listed as
2004
186,771
3,533
1.9%
threatened or endangered under the ESA. During the 115th
2005
81,252
2,920
3.4%
Congress, several bills were introduced that would provide
2006
105,063
3,401
3.1%
greater flexibility for lethal removal of sea lions in specific
segments of the Columbia River and its tributaries. One of
2007
88,474
4,355
4.7%
these bills, S. 3119, has passed the Senate and the House.
2008
147,558
4,927
3.2%
2009
186,056
4,960
2.7%
Background
2010
267,167
6,321
2.4%
Sea Lion and Salmonid Populations
2011
223,380
3,970
1.8%
Over the last several decades, California sea lions
2012
171,665
2,360
1.4%
(Zalophus californianus) and the eastern population of
2013
120,619
2,928
2.4%
Stellar sea lions (Eumetopias jubatus) that inhabit the U.S.
2014
219,929
4,621
2.1%
West Coast have steadily increased. The California sea lion
population has never been listed under the ESA and is
2015
239,326
10,859
4.3%
estimated to be within the range of its optimum sustainable
2016
154,074
9,525
5.8%
population (OSP). OSP is defined as the number of animals
2017
109,040
5,384
4.7%
that will result in the maximum productivity of the
population of the species. The eastern population of Stellar
Source: Tidwell et al., Evaluation of Pinniped Predation on Adult
Salmonids and Other Fish in the Bonneville Dam Tailrace, 2017, U.S.
sea lions was delisted from the ESA in 2013 and likely is
Army Corps of Engineers, Portland District, March 5, 2017.
within the range of its OSP.
Notes: The data are for adult salmonids (adults and jacks) and
Salmonids (Oncorhynchus spp.) are anadromous fish,
include wild and hatchery fish.
meaning they hatch and begin life in freshwater rivers and
Deterrence and Removal of Sea Lions
lakes, migrate to the ocean, where they mature, and return
to their river of origin to spawn. The current run sizes of
wild salmonids in the Columbia Basin are a small fraction
MMPA Requirements
of historic levels. From January through May of each year,
The MMPA prohibits any person subject to the jurisdiction
the bulk of salmonids consumed by sea lions in the vicinity
of the United States from “taking” marine mammals,
of Bonneville Dam are spring Chinook and winter
including sea lions. Take “means to harass, hunt, capture, or
steelhead. Sea lions also prey upon other Columbia River
kill, or attempt to harass, hunt, capture or kill any marine
salmon runs and other species, such as sturgeon, eulachon,
mammal.” The MMPA provides an exception for nonlethal
and Pacific lamprey.
efforts to deter nuisance animals—such as sea lions—if
conducted by authorized personnel. Nonlethal taking must
In the 1990s, increasing numbers of California sea lions
be done in a humane manner, and all practical steps must be
were observed in the lower Columbia River. By 2000, sea
taken to avoid death to or injury of the animal.
lions were observed at Bonneville Dam and, more recently,
at the base of Willamette Falls. Sea lions prey upon
Section 120 (16 U.S.C. §1389) of the MMPA provides an
salmonids, especially in areas where the returning fish
exception for lethal removal when nonlethal actions are not
gather to pass through areas where river flows are
successful. Under Section 120, a state may apply to the
constricted, such as near fish ladders or at the base of
Secretary of Commerce to intentionally euthanize sea lions
rapids. Predation of salmon and steelhead immediately
when individually identifiable sea lions or seals are having
below Bonneville Dam (146 miles above the mouth of the
a significant negative impact on salmonids that have been
Columbia River) has been increasing (Table 1). Since
listed as threatened or endangered or are approaching
2004, Stellar sea lions have consumed a growing portion of
threatened or endangered status under the ESA. Before
salmonids preyed upon by sea lions in the vicinity of
lethal removals are allowed, the Secretary decides whether
Bonneville Dam.
sufficient evidence exists to establish a Pinniped-Fishery
Task Force to review public comments, population and
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Sea Lion Predation on Columbia River Salmon and Steelhead
biological trends, past efforts, and harm to salmonid
were granted renewal of the authorization for lethal removal
populations. The Secretary is required to consider the task
of sea lions in areas adjacent to Bonneville Dam through
force’s recommendations, public comments, and whether
June 2021, under the same conditions as the 2012
the applicant has already taken all reasonable, nonlethal
authorization. Sea lions also consume ESA-listed salmonids
measures. Nonlethal and lethal taking are prohibited if the
that spawn in the upper Willamette River, a Columbia River
marine mammal population is a depleted stock (endangered
tributary. In 2018, the state of Oregon requested and was
or threatened under the ESA) or a strategic stock under the
granted an authorization for the lethal take of up to 92
MMPA.
California sea lions per year at Willamette Falls.
Efforts in the Columbia Basin
Congressional Action
Federal, state, and Columbia River Inter-Tribal
In the 115th Congress, several bills have been introduced in
Commission representatives have cooperated in developing
the House and Senate that would amend the MMPA. Each
nonlethal efforts to deter sea lions, such as above-water and
bill would provide greater flexibility to remove sea lions for
below water pyrotechnics, barriers to fish passage
the purpose of protecting salmonids and other fish species.
entrances, high-pressure water spray, boat chases, rubber
H.R. 2083, S. 3119, and S. 3315 include similar provisions
bullets, and capture and transfer to other areas. Generally,
that would
deterrence has been ineffective in the long run because sea
lions have adapted to or ignored most of these measures, or
expand the geographic area of the Columbia River and
they have returned after transport and release to other areas.
its tributaries where sea lions may be lethally removed,
Figure 1. California Sea Lions Authorized for Lethal
change the requirements for individual identification to
Removal and Actual Removals
include all sea lions found in these areas,
increase lethal removal of sea lions in a given year to no
more than 10% of PBR, and
include certain regional tribes as entities that would be
eligible to remove sea lions.
On December 6, 2018, the Senate passed S. 3119; the
House passed it on December 11, 2018. Earlier in the
session, the House passed H.R. 2083.
Differing Views
In 2006, the Marine Mammal Commission (MMC)
concluded that if the choice is between the conservation of
endangered and threatened salmonids and the removal of
Source: Tidwell et al., Evaluation of Pinniped Predation on Adult
individual sea lions from healthy stocks, the MMPA directs
Salmonids and Other Fish in the Bonneville Dam Tailrace, 2017, U.S.
that the conservation of the salmonids stocks take
Army Corps of Engineers, Portland District, March 5, 2017.
precedence. MMC also has questioned whether there is
evidence that lethal removals have been effective; it has
In 2008, the Secretary authorized lethal removal of 1% of
supported additional data collection and monitoring that
California sea lion potential biological removals (PBR), a
could be used to improve program evaluation.
total of 85 animals per year, which was increased to 92
animals in 2012. PBR is defined as the number of animals
According to the Oregon Department of Fish and Wildlife
that may be removed from a marine mammal stock while
(ODFW), removal of problem sea lions has proven to be the
allowing the stock to reach or maintain its OSP. Before an
most effective means of protecting fish from predation.
animal can be considered for removal, the sea lion must be
ODFW states that if sea lion predation is not addressed,
individually distinguishable, either by unique natural
constraints on other economic activities, such as power
markings or by applied features such as brands. To remove
generation, fisheries, and land use, likely will increase and
an individual, the sea lion must have been observed
salmonid runs may be lost. However, the task force
minority opinion has countered that sea lion predation is
eating salmonids in the areas below Bonneville Dam at
insignificant when compared to take of salmonids by
any time between January 1 and May 31;
humans. They contend that the life history of salmonids has
made their populations vulnerable to environmental
in the area below Bonneville Dam on a total of any five
degradation caused by activities such as forestry, mining,
days (during a single year or over multiple years); and
agriculture, and hydroelectric generation. They add that
these activities have been the main contributor to historical
below Bonneville Dam after having been subject to
declines of salmon populations.
active nonlethal removal.
Harold F. Upton, Analyst in Natural Resources Policy
Historically, the number of animals removed and
euthanized has been much lower than the number
IF11045
authorized (Figure 1). In 2016, the states requested and
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Sea Lion Predation on Columbia River Salmon and Steelhead
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