Columbia River salmon and steelhead face a serious threat from California sea lions that prey on fish waiting to move up the fish ladders at Bonneville Dam in early spring. Each year since 2002, sea lions have consumed thousands of migrating fish, many from threatened and endangered runs protected under the federal Endangered Species Act (ESA).
The federal Marine Mammal Protection Act recognizes that predation by a growing sea lion population can jeopardize salmon and steelhead stocks at risk of extinction. For the past seven years, wildlife managers from Washington and Oregon have worked with federal and tribal partners to chase sea lions away from the area immediately below Bonneville Dam. But these efforts, alone, have not proven effective in curbing salmon predation by a robust population of California sea lions.
In March 2008, fish and wildlife agencies in Washington, Oregon and Idaho received federal authorization to remove California sea lions that have been observed preying on salmon and steelhead below Bonneville Dam. The federal authorization allows wildlife managers to use lethal measures to remove sea lions that meet specific criteria, although the states’ first priority has been to relocate them to zoos and aquariums.
Through 2014, wildlife managers removed a total of 73 California sea lions – 13 of which were sent to zoos and aquaria – that met the federal criteria. The number of salmon consumed by sea lions below the dam has declined in the past two years, but predation rates are still in the thousands and it is too early to assess the long-term effectiveness of those efforts.
In 2015, the Oregon Department of Fish and Wildlife and partnering agencies will mark their 11th straight year in the ongoing effort to manage sea lions preying on protected Columbia River salmon runs.
2015 California sea lion trapping at Bonneville Dam
Week of May 18
Eight California sea lions on the list for removal were trapped and euthanized. An additional 32 California sea lions not on the list for removal were trapped, branded and released.
Week of May 11
Ten California sea lions on the list for removal were trapped this week. Eight were euthanized and two are being processed for transfer to the Queens Zoo. An additional 20 California sea lions not on the list for removal were trapped, branded and released.
Week of May 4
Trapping and removal operations at the dam remain suspended due to the accidental death of a Steller sea lion on Monday night. See more details. Staff spent the remainder of the week inspecting and modifying the traps to prevent a similar incident in the future.
Week of April 27
Two California sea lions on the list for removal were trapped and euthanized. Twenty-three California sea lions, not on the list for removal, were trapped, branded and released. A trap malfunction sometime Tuesday night/Wednesday morning resulted in the accidental death of two California sea lions (not on the list for removal). For more information.
Week of April 20
]Five California sea lions on the list for removal were trapped and euthanized. Twenty-seven California sea lions, not on the list for removal, were trapped, branded and released.
Week of April 13
One California sea lion on the list for removal was trapped and euthanized. Sixteen California sea lions, not on the list for removal, were trapped, branded and released.
Week of April 6
Six California sea lions on the list for removal were trapped and euthanized. Thirteen California sea lions, not on the list for removal, were trapped, branded and released.
Learn more about why California sea lions are being removed from the Columbia River (pdf)
Summaries of sea lion trapping
Section 120 Authority to remove sea lions
In March 2012, NOAA Marine Fisheries issued a letter authorizing (pdf) the states to remove specific California sea lions eating threatened salmon and steelhead in the Columbia River. The authorization stays in effect until June 1, 2016. The authorization allows the states to remove up to 93 California sea lions a year; these animals must meet the following criteria:
- Must be individually identifiable through natural or applied features (usually a brand)
- Have been observed eating salmonids in the Bonneville Dam area between Jan. 1 and May 31 of any year
- Have been observed on a total of any five days (consecutive days, days within a single season, or days over multiple years) between Jan. 1 and May 31
- Have been subjected to but not responded to non-lethal hazing
Visit the NOAA Marine Fisheries Website for more information about the Section 120 application and authorization.
Pinniped Branding on the West Coast (pdf)
California sea lion predation has been identified as a concern in the Draft Upper Willamette River Salmon and Steelhead Recovery Plan, which describes the many factors having a negative impact on salmon and steelhead populations in the basin.
Again in 2015, an ODFW observation program at the Willamette Falls in Oregon City will monitor sea lion foraging activity from Willamette Falls to the mouth of the Clackamas River in order to estimate total salmon, steelhead, sturgeon and lamprey predation by sea lions.
Changes to the program include starting three weeks earlier and encompassing a greater range of daylight hours over the course of the 16 week study. Despite the early start, however, there were already at least 6 California sea lions and 2 Steller sea lions foraging below the Falls the week before the study began.
ODFW discontinued hazing at Willamette Falls after 2013 in order to shift the agency’s limited resources to a new monitoring program focused on obtaining predation estimates at the Falls. (Hazing efforts had been somewhat effective in moving California sea lions downstream and away from the entrances to the fish ladders at the Falls. However, once the hazing stopped predator activity would resume.)
The results from the 2014 monitoring efforts can be found in this report (pdf). Highlights from this report include:
- Based on 13 weeks of observation from March 3 to June 1, an estimated 3,700 salmonids (+/-400) were taken by sea lions, as well as 500 lamprey and 60 sturgeon.
- Based on run proportions at the fish-counting window, it was estimated that approximately 800 listed winter steelhead were taken by sea lions (or 13 percent of the potential escarpment above the falls) and over 500 listed wild spring Chinook (or 8 percent of potential escapement).
- Estimated predation is known to be an undercount because observations started after sea lions had already arrived in February and estimates only applied to daylight hours from 7 am to 6 pm.