Cormorant Management

Cormorants on East Sand Island

The Corps began studying the impacts of avian predation on juvenile salmonids in the Columbia River Estuary in 1997. The research on East Sand Island contributes to understanding the impacts double-crested cormorants (DCCO) have on juvenile salmonids, which are listed as threatened or endangered under the Endangered Species Act (ESA), as they migrate out to the ocean. East Sand Island's DCCO colony grew from approximately 100 pairs in 1989 to a peak of 14,916 nesting pairs in 2013, which accounted for more than 40 percent of the western population and was the largest breeding colony in North America. After over 15 years of research, the Corps developed and began implementing a management plan to reduce the impacts of DCCO predation on juvenile salmonids.

2018 Management Updates

In 2018, the Corps identified 1.2 acres on the western-most portion of East Sand Island where DCCO could nest undisturbed by human hazers during the breeding season. Based on nest densities from previous years, the Corps estimated that approximately 5,400 breeding pairs of DCCO could nest in the 1.2 acre colony, consistent with the goals of the management plan. Corps contractors constructed a privacy fence to delineate the colony area from the remainder of the island and they installed cameras to detect and monitor the breeding colony remotely.

Corps contractors completed site preparations on the colony area on April 9 and initiated monitoring surveys on April 25. DCCO began loafing on beaches at East Sand Island in mid-April, but did not begin roosting overnight breeding behaviors mid-May.

Several adult and juvenile bald eagles (Haliaeetus leucocephalus) were present on the island in late April. Eagle presence and predatory behavior influenced the stability of the DCCO breeding colony, flushing adults and predating nests with increasing frequency in May and June before tapering in early July, following a decrease in river levels. Following the departure of eagles from the island in early July, the DCCO stabilized and grew to its peak colony size of 3,672 active nests (95% CI = 3,662 – 3,682) on July 25. As described in the 2015 management plan, the peak breeding season colony size was enumerated by counting the number of active nests observed in late incubation during the nesting cycle (FEIS Chapter 5, Page 22). Due to the disturbances by bald eagles and gulls, the timing and status of nest activity throughout the colony varied widely. Staff observed the first DCCO egg May 20, and DCCO were still laying and incubating eggs in early August when the first chicks fledged from nests. Colony monitoring effects concluded in late September as DCCO juveniles fledged from nests and foraged in the estuary.

We limited our management effects in 2018 to hazing adults and collecting a limited number of eggs to ensure the colony size did not exceed management goals (5,380-5,939 breeding pairs), per the management plan. In addition, the Corps used passive dissuasion measures effectively in some areas, including the use of reflective tape, balloons, and eagle and coyote effigies; however, we needed repeated human presence in other areas to prevent the successful establishment of nests. In total, the team collected three eggs from East Sand Island over the course of the breeding season and hazing was successful at eliminating nest attempts on portions of the island outside of the designated colony. These efforts supported the Corps’ efforts to maintain the colony size goals outlined in the 2015 management plan while simultaneously supporting a DCCO breeding colony on ESI.

In 2018, the USFWS coordinated efforts to estimate the size of the Western Population of DCCO in conjunction with the Pacific Flyway Council’s monitoring strategy. The Corps supported these efforts by funding surveys at sites where data would not otherwise be collected by other entities. This allowed monitoring of 43 sites and allowed surveying of an additional 80 sites, for a total of 123 colony sites or colony complexes monitored and analyzed. Results are pending as the data is preliminary and not yet finalized; when USFWS finalizes the data, we will update the results.


2018 Cormorant Breeding Season

Based on monitoring results from the 2017 breeding season, and per guidelines established in the DCCO Management Plan, the Corps determined that lethal removal under Phase I activities is no longer warranted and management will transition into Phase II activities for the 2018 breeding season. Phase II activities consist primarily non-lethal methods to limit population size before modifying nesting habitat on East Sand Island following the breeding season. The Corps delineated a designated nesting area on the western-most portion of East Sand Island which can support up to 5,900 breeding pairs.

Outside of the designated nesting area (all areas east), DCCO will be hazed and dissuaded from establishing active nests. Management activities will be supplemented with limited egg take, as necessary and within the limit authorized by USFWS, to support maintenance of a breeding colony with no more than 5,900 breeding pairs on East Sand Island. Following a request by the Corps, the USFWS issued an annual depredation permit on April 19, 2018  for the collection of up to 500 eggs on East Sand Island and up to 250 eggs on sites in the upper estuary where the Corps places sandy material dredged from the navigation channel. Site preparation activities were conducted between March 21 and April 9, 2018 and included construction of a barrier fence to delineate the designated nesting area west of the former breeding colony.

The 2018 nesting area is 1.3 acres. A fence provides a visual barrier to minimize disturbance to DCCO nesting on the western portion of the island and prevent dispersal to other, off-island locations. A monitoring blind was relocated adjacent to the fence to support monitoring throughout the breeding season. In addition, multiple cameras are deployed throughout the island to remotely monitor DCCO presence and observations between on-island site visits.


Why do we need a management plan?

In 2008, NOAA Fisheries issued a Biological Opinion on the operations of the hydropower dams that make up the Federal Columbia River Power System (FCRPS). NOAA Fisheries concluded that operating the FCRPS in accordance with the BiOp would not jeopardize the continued existence of ESA-listed species; nor would it adversely modify or destroy the species’ critical habitat if the action agencies implemented the BiOp’s recommended reasonable and prudent alternative (RPA). The RPA includes improving fish passage at dams, managing flow, controlling predators that prey on young salmon, improving tributary and estuary habitat and reforming hatchery practices. Two RPA actions from the 2008 FCRPS BiOp specifically address management of double-crested cormorants in the Columbia River Estuary.

• RPA action 46 requires the development of a management plan for double-crested cormorants in the Columbia River Estuary and implementation of warranted actions in the estuary.

• RPA action 67 requires the double-crested cormorant population in the Columbia River Estuary and its impact on out-migrating juvenile salmonids to be monitored and implementation of a management plan to decrease predation rates, if warranted.

Research Supporting Development of Management Plan

The Corps has been conducting research studying the impact of avian predation on juvenile salmonids in the Columbia River Estuary since 1997. The research on East Sand Island contributes to understanding of the impacts cormorants have on juvenile salmonids migrating out to the ocean.

In 2008, the Corps began small-scale management feasibility studies on the DCCO colony, restricting the birds from nesting in specific locations on East Sand Island. Study methods included hazing with lights, reducing nesting habitat and using human presence to flush double-crested cormorants off potential nesting sites. In 2011, the Corps’ research focused on reducing the amount of available nesting habitat for DCCO on the western portion of the island and tracking the dispersal of radio- and satellite-tagged individuals. Habitat reduction was primarily accomplished by installing barrier fences and using human hazers to flush birds from areas outside of the designated nesting area.

In 2013, the DCCO colony was restricted to 4.4 acres. Eighty-three adult DCCO were marked with satellite transmitters and several hundred adults were banded with leg bands to provide information about where individuals would move during the dissuasion efforts. Although reduced by 70 percent, available habitat was not completely limited and 14,900 breeding pairs ultimately nested on the island. Near-term dispersal locations of radio and satellite tagged DCCO during the 2011–2013 breeding seasons were generally to four main areas identified in geographic proximity to East Sand Island:

• Columbia River Estuary (defined as the tidally influenced 172 river miles from the mouth of the Columbia River to Bonneville Dam, including the Willamette River down to Willamette Falls Locks)
• Outer Washington coast (Willapa Bay and Grays Harbor)
• Puget Sound
• Northern Salish Sea (San Juan Islands, Strait of Georgia, Vancouver, BC) (BRNW 2014)

Of these areas, the Columbia River Estuary has had the highest levels of use by DCCO during the dissuasion research in 2012 and 2013. There were no confirmed detections of radio- or satellite-tagged DCCO at inland sites east of The Dalles Dam, or at coastal sites south of Cannon Beach, Oregon.

The graphs below show the impact of the cormorant colony on East Sand Island to salmonids prior to initiating management activities in 2015. The first graph shows annual consumption of juvenile salmonids by the colony. The second graph shows the seasonal proportion of salmon the double-crested cormorants consume during their nesting season.

The Double-crested Cormorant Management Plan

In 2014, the U.S. Army Corps of Engineers released a draft Environmental Impact Statement and management plan to reduce predation of juvenile salmon and steelhead by DCCO in the Columbia River Estuary. In developing the plan, the Corps worked closely with the following cooperating agencies: the U.S. Fish and Wildlife Service (USFWS), the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service - Wildlife Services (APHIS-WS), the Oregon Department of Fish and Wildlife (ODFW) and the Washington Department of Fish and Wildlife (WDFW).

In 2015, the Corps prepared and released the final Environmental Impact Statement on February 6, 2015. Brigadier General John Kem, the U.S. Army Corps of Engineers Northwestern Division commander, signed a Record of Decision (ROD) for the Double-Crested Cormorant Management Plan Final Environmental Impact Statement March 19, 2015. The ROD documents the Corps’ decision and rationale for adopting the management plan to reduce predation on juvenile salmon and steelhead listed under the ESA by the DCCO population in the Columbia River estuary.

The Corps selected alternative C-1 in the final EIS to carry out actions in the management plan through a two-phased management approach for reducing the DCCO population in the Columbia River Estuary. In Phase I, actions included lethal removal (culling) individuals and oiling eggs to achieve a colony size of about 5,600 breeding pairs by 2018. In Phase II, long-term habitat modifications on the western portion of East Sand Island will limit the availability nesting habitat by inundating much of the existing colony area. In addition, management activities may include hazing and dissuasion supported with limited egg take to maintain an average colony size of 5,600 breeding pairs.

Alternative C-1 uses adaptive management methods to determine each year’s actions. The Corps’ works closely with the USFWS migratory bird office when developing each year’s management actions. In determining the specific objectives for each year, including the number of individuals to cull or eggs to oil, the USFWS analyzes the long-term sustainability of the DCCO colony at East Sand Island and throughout the western population. The Corps annually requests a depredation permit from the USFWS to carry out and implement management actions and the numbers of individuals and eggs authorized for removal each year are based on the previous year’s breeding population and the USFWS’ analysis of long-term sustainability of the western population.

The Corps began implementation of the management plan in 2015. To date, Phase I activities were conducted in 2015, 2016 and 2017 and a total of 5,576 adult cormorants were lethally removed from the breeding population and 6,181 nests destroyed. The table below provides the peak breeding population at the end of breeding season and the associated numbers of birds culled and nests destroyed relative to the amounts authorized in the annual depredation permits. In 2017, the DCCO colony dispersed from East Sand Island for the majority of the breeding season, with approximately 1,100 individuals returning in late June to establish nests and rear young.

Number of adult cormorants culled and nests oiled for the reporting period

Year Peak Population (Breeding Pairs) Authorized Take Total Take
2014 13,626 N/A N/A
2015 12,150 3,489 adults
5,879 nests
2,346 culled
5,089 nests oiled
2016 9,774 3,114 adults
5,247 nests
2,982 culled
1,092 nests oiled
2017 544 2,408 adults
4,058 nests
248 culled
0 nests oiled
2018 -- 500 eggs (East Sand Island)
250 eggs (dredge placement sites)


Western Population Monitoring

The Pacific Flyway Council is an administration composed of directors or appointees from the public wildlife agencies in each state and province of the western United States, Canada, and Mexico. In the U.S., the Pacific Flyway includes Alaska, Arizona, California, Idaho, Nevada, Oregon, Utah, Washington, and those portions of Colorado, Montana, New Mexico and Wyoming west of the Continental Divide. The USFWS has a lead representative who works with the Flyway Council and associated technical committee to share information and develop management recommendations for migratory bird conservation.

In July 2012, the Council finalized their plan  A Framework for the Management of Double-crested Cormorant Predation on Fish Resources in the Pacific Flyway. This plan provides a framework to follow when addressing fish depredation issues involving DCCO, and includes information concerning biology, status, resources conflicts, management options, regulatory requirements and recommended management strategies. The Corps evaluated the plan for consistency with the alternatives identified in the FEIS.

In 2013, the Pacific Flyway Council published A Monitoring Strategy for the Western Population of Double-Crested Cormorants. The Pacific Flyway Monitoring Strategy is a coordinated monitoring effort to estimate the breeding size, trend, and distribution of the western population of DCCO across the Pacific Flyway. As a part of the DCCO Management Plan, the Corps provides supplemental funding to USFWS to support monitoring efforts where and when colonies are not funded in any given year during implementation of the management plan. This monitoring is used to detect potential changes in the size of the western population of DCCO relative to management actions implemented at East Sand Island. The USFWS evaluates the status of the western population at the end of the breeding season and prepares a summary report documenting monitoring methods and results. The annual reports for 2015, 2016 and 2017 are provided herein.

Cooperating Agencies

The Corps is the lead agency on the Environmental Impact Statement under the National Environmental Policy Act. The following agencies are cooperating: U.S. Fish and Wildlife Service; U.S. Department of Agriculture's Animal and Plant Health Inspection Service-Wildlife Services; the Oregon Department of Fish and Wildlife; and the Washington Department of Fish and Wildlife.