the film forum library tutorial contact DONATE

Northwest Power/Conservation Council Gets The Stats on Avian Predation of ESA Salmon Smolts by Staff Columbia Basin Bulletin, September 21, 2026

Avian predation of Snake River Chinook salmon smolts was about 10 percent in 2025

Water birds in the Columbia River basin consume large numbers of out-migrating juvenile salmon and steelhead every year. Three government management plans targeting four avian predator breeding colonies have met with mixed results, according to a recent report by Northwest experts.

At one time, the Columbia River hosted the largest Caspian tern and double-crested cormorant breeding colonies in the world on East Sand Island in the river's estuary, as well as two large Caspian tern colonies in the Columbia Plateau region on Crescent Island in the McNary Reservoir and on Goose Island in the Potholes Reservoir.

Prior to setting two of the management plans in motion, Caspian Terns and Double-crested Cormorants nesting on East Sand Island in the river's estuary took up to 25 million salmonid smolts annually. That's around 15 percent of the smolts passing the island, which is about 8 miles upstream of the ocean. The third management plan addressed terns nesting on Crescent and Goose islands in the Columbia Plateau which consumed 5 percent to 30 percent of smolts, mostly of steelhead listed under the federal Endangered Species Act.

Overall, bird predation of Columbia and Snake River steelhead was high in 2025 at about 35 percent of the outmigration and has been 20 to 50 percent of the outmigration every year since 2008.

Avian predation of Snake River Chinook salmon smolts was about 10 percent in 2025 and has been 5 to 20 percent of the run every year since 2008.

And, predation on endangered Snake River sockeye salmon smolts was about 25 percent in 2025 and 5 to 30 percent since 2008. In addition, American white pelicans took up to 40,000 adult sockeye headed into the upper Columbia or Snake rivers.

Allen Evans, a fisheries scientist with Real Time Research in Bend, OR, updated the Northwest Power and Conservation Council at its September meeting about the results of a 2025 annual report on avian predation in the Columbia River basin.

See Avian Predation in the Columbia River Basin: 2025 Final Annual Report.

According to Evans, piscivorous colonial waterbird species such as Caspian terns, double-crested cormorants and gulls, migrate from the south and breed in colonies in the Columbia River at the same time that salmon and steelhead smolts are migrating downriver. Other water birds of concern are Brandt's cormorants, California gulls and ring billed gulls, American white pelicans, great blue herons and great egrets, he said.

The purpose of the three management initiatives was to "reduce predation rates (proportion of available smolts consumed) on ESA-listed salmonid populations by reducing the size or eliminating the colonies identified in management plans," the Sept. 1 Council Memorandum said (2026_09_3.pdf). "As part of the management plans, adaptive management actions have been conducted at various other colony locations where birds that were displaced from the managed colonies have relocated to nest."

For the annual report, scientists monitored 36 water bird colonies. The highlights of the report are:

1. Overall results show that the cumulative effects of avian predation/consumption remain a substantial source of smolt mortality in the Columbia River Basin, particularly for ESA-listed steelhead and sockeye populations.

2. The ongoing management of tern colonies in the Columbia Plateau areas of the river has resulted in a shift in the number and location of tern colonies.

3. In addition, a primary goal of the Columbia Plateau Management Plan is to reduce predation rates on smolts by terns to less than 2 percent per ESA-listed salmonid population, per colony. In 2025, that objective was achieved, except for a colony on Banks Lake, WA, where an estimated 2.2 percent of upper Columbia River steelhead were consumed. "However, the predation rates by terns that have re-nested on Crescent Island will require further adaptive management to achieve Plan goals in the future," the Council Memo says.

4. Predation on smolts by other waterbird species indicates that smolt consumption rates were highly variable depending on the predator species, colony location, colony size and salmonid species. As an example, predation rates by gulls has surged in some locations.

Greatest impacts in 2025 were on Upper Columbia River and Snake River steelhead, with individual tern colonies consuming upwards of 2 percent of available steelhead smolts Management of the birds by the U.S. Army Corps of Engineers and the U.S. Fish and Wildlife Service was set in motion 2000 - 2007. Predation rates at East Sand Island and Goose Island colonies are down as much as 80 percent, but the colony of terns at Crescent Island is reestablishing itself.

Although colony size objectives were met or exceeded, the Pacific flyway population of Caspian terns has decreased by about 70 percent since 2008, and, according to Evans the decline threatens the Pacific Flyway population.

Double-crested cormorants

The report identified eleven double-crested cormorant breeding sites in 2025, with the largest by far at the Astoria-Megler Bridge in Astoria, OR (5,310 pairs; amongst the highest number observed to-date). Other nesting sites in the estuary are at the Lewis and Clark Bridge and Troutdale Towers. Other colonies in the upper estuary and Columbia Plateau Region are also increasing in size, with the largest inland colony on Crescent Island (534 pairs).

Cormorants on the Astoria bridge eat more than 10 percent of listed ESA salmon and steelhead that pass through the area. Predation at Crescent Island is 5 percent.

"Despite the management of the ESI cormorant colony (2015 - 2019), cormorant predation rates in 2025 were amongst the highest observed to-date due to increases in colony sizes upstream of ESI (East Sand Island), where per capita (per bird) predation rates are significantly higher than those previously documented on ESI," Evans said in his presentation.

Gulls

The report identified multiple gull species and nine breeding sites in 2025, with the largest colonies on Goose Island (11,150 individuals), Island 20 (9,189 ind.), Miller Rocks (4,915 ind.) and Crescent Island (3,215 ind.), all in the Columbia Plateau.

Colonies located on the mainstem Columbia River (Island 20, Crescent Island and Miller Rocks) posed the greatest threat to smolt survival, with predation rates of 5 to 11 percent of salmon and steelhead populations, which were amongst the highest observed to-date, according to Evans. Predation by colonies located more than 30 kilometers (18.5 miles) from the Columbia River, however, posed little to no threat with predation rates less than 1 percent.

So far, there are no federal management plans at the colony-level for gulls. Dissuasion efforts by the Yakama Nation on Miller Rocks did not substantially reduced predation. In 2026 gulls abandoned the breeding site on Miller Rocks in May, but a colony has since formed 13 km upstream in The Dalles Reservoir.

American White Pelicans

The report identified two colonies of American white pelicans, one in the estuary on Miller Sands Spit (1,168 individuals) and one in the Columbia plateau on Crescent Island (2,816 individuals). The largest colony of pelicans had been on Badger Island in the McNary Reservoir but is now on Crescent Island.

There is evidence that pelican numbers in the Columbia River basin have increased over the last 10 - 15 years, Evans said.

Predation rates by pelicans are low (less than 1 percent) on yearling smolts in the Columbia River. Predation on sub-yearling smolts and fish in tributary systems (such as the Yakima and Umatilla rivers) can, however, be substantial (greater than 10 percent).

Predation on adult Sockeye Salmon can be as much as 8 percent of the run arriving at Bonneville Dam in some years, which equates to more 40,000 adults, Evans said.

Herons

There are six main breeding sites for herons, all arboreal (in trees) and smaller-sized colonies. The largest is on Island 20 in the middle Columbia River (114 breeding pairs).

Heron tend to forage near their breeding site with predation rates on smolts in the Columbia River low (less than 1 percent). They are capable of consuming larger-sized fish, Evans said, but there is no evidence they consume adult salmon and steelhead.

Emerging Issues

The East Sand Island Caspian tern colony is now well below the target colony size of 3,125 pairs with little to no productivity (young). Pacific Flyway population has declined by an estimated 70 percent.

Predation by double-crested cormorants in the middle to upper Columbia River estuary (especially on the Astoria/Megler Bridge) is now greater than that of predation by birds that formerly nested on East Sand Island in the lower estuary, with rates of more than 10 percent on salmon and steelhead.

Double-crested cormorant predation is increasing at several Columbia plateau colonies, such as at Crescent Island (now the largest plateau cormorant colony) with predation rates of 5 percent on Snake River sockeye and Snake River steelhead in 2025.

Predation rates by gulls breeding at sites located on the mainstem Columbia River in 2025 were amongst the highest ever recorded, with rates of more than 8 percent per colony on Snake River steelhead, upper Columbia River steelhead and Snake River sockeye. Cumulative effects in 2025 were greater than 20 percent of available smolts for some species, Evans said in his presentation.

Numbers of American white pelicans have been increasing over the last two decades. Predation on smolts and on adult sockeye Salmon can be substantial.

Per capita (per bird) consumption rates by gulls and pelicans are lower than those of terns and cormorants, but predation can be substantial, particularly for colonies located near dams, diversion sites, tributaries, and other areas where fish congregate.

Related Pages:
Less Nesting Habitat Has Led to Higher Nesting Density for Salmonid-Eating Caspian Terns by Staff, Columbia Basin Bulletin, 3/13/15
Mid-Columbia Efforts to Reduce Avian Predation Result in Survival Increase for Juvenile Salmonids by Staff, Columbia Basin Bulletin, 2/20/15
Final EIS Released on Reducing Estuary Cormorant Numbers; Proposes Both Shooting and Egg Oiling by Staff, Columbia Basin Bulletin, 2/6/15
Research Tracks Movements, Steelhead Predation by Caspian Terns in Mid-Columbia Basin by Staff, Columbia Basin Bulletin, 1/3/14
Plan Set to Limit Mid-Columba Bird Predation by Staff, Columbia Basin Bulletin, 2/7/14
Final EIS Released on Reducing Estuary Cormorant Numbers; Proposes Both Shooting and Egg Oiling by Staff, Columbia Basin Bulletin, 2/6/15