Annual update on avian predation in the basin highlights emerging challenges

Allen Evans, Fisheries Scientist with Real Time Research, Dr. Rachel Orben, Assistant Professor, Oregon State University, and James Lawonn, Oregon Department of Fish and Wildlife and facilitator of the informal Columbia Basin Avian Predation Work Group, presented an annual update on avian predation in the Columbia River Basin at the August Council meeting (read presentation | watch video). The Council has received a range of recommendations related to avian predation as part of the current Columbia River Basin Fish and Wildlife Program amendment process, including calls for more regional coordination. Predator management, which includes birds, fish, and mammals, is part of the Council’s 2014 Fish and Wildlife Program and the 2020 Addendum.

Avian predation, particularly species like Caspian terns, double-crested cormorants, gulls, and, increasingly, American white pelicans, has been a cause of concern across the basin due to their impacts on out-migrating juvenile salmon smolts. For example, avian predation can contribute up to half of annual smolt mortality in Upper Columbia River steelhead. It has a lesser impact on Snake River yearling Chinook, contributing 20-25% of annual mortality, according to Evans.

“We have a kind of unique situation where we have protected birds eating protected fish, and of course humans are part of that equation as well,” said Evans.

Evans also touched on additive versus compensatory predation. Additive mortality means that predation adds additional mortality to the system; compensatory mortality means that the fish that predators eat would have died anyway, so it does not add to mortality.

“This is a pretty complicated question to answer in big systems like the Columbia River Basin where you have a lot of different fish species, a lot of different predators, huge spatial scales, and huge time scales, where not only do you have predation on smolts but you’re also interested in how many adults survive to come back....This is where the rubber meets the road because it tells you, if you manage a particular predator, are you going to get fish back?”

Management plans over the last decade or so have included a mixture of non-lethal methods, including hazing, reducing nesting areas, and creating alternative habitat, as well as lethal methods like culling adults and oiling eggs. Monitoring has been used to inform adaptive management decisions under changing conditions. However, management efforts have had varying degrees of success and have sometimes resulted in unintended consequences, such as the increase of nesting cormorants on the Astoria-Megler Bridge near Astoria, Ore., that were displaced from a site further downriver.

Evans gave an overview of the different populations under management and emerging issues:

Caspian Terns 

Evans noted particular characteristics of Caspian terns that make them a priority species, including disproportionate consumption of steelhead smolt that can reach 20% of available steelhead at certain colonies, as well as a high degree of nest fidelity. Management of Caspian terns at East Sand Island and Goose Island near the mouth of the Columbia has resulted in an appreciable decrease in predation on steelhead smolts by about 70% since 2020. However, due to a combination of management techniques and the impacts of avian influenza, long-term viability of Caspian terns in the region is now a concern. According to Evans and Orben, as of 2024, the Pacific Flyway population has declined by about 71% since 2009. East Sand Island, an artificial dredge island, had previously been home to the world’s largest breeding colony of Caspian terns. 

Double-crested cormorants 

Following large-scale management interventions between 2015-2019, including culling, egg oiling, and reduced nesting habitat, cormorants dispersed from East Sand Island as intended. However, the colony at the Astoria-Megler Bridge grew substantially as a result, from 300 pairs in 2014 to over 5,300 pairs in 2024, with other upriver nesting sites also seeing an increase. This has meant an increase in predation on ESA-listed salmon and steelhead stocks due to the relative consumption of these species increasing as birds move upstream. It has also created urgent human safety and traffic concerns related to the bridge. Plans are uncertain, but management options include reducing cormorant nesting in the upper estuary and attempting to re-establish the East Sand Island colony at the desired levels. 

Gulls and American White Pelicans 

Evans said gulls and American white pelicans are a growing concern in the basin. American white pelicans have increased their population over the last two decades and are known to consume adult salmonids in addition to subyearling smolts. A recent study completed by Real Time Research and the U.S. Geological Survey showed that pelicans on Badger Island near the Tri-Cities were consuming about 8%, or 40,000 fish, of the sockeye arriving at Bonneville Dam. Evans noted that more research was needed to better understand the impacts of pelicans, and called for more comprehensive and larger-scale research, monitoring, and evaluation of avian predation across the basin.  

Columbia Basin Avian Predation Work Group

James Lawonn then spoke about the work being done by the informal Columbia Basin Avian Predation Work Group, which includes representation from states, tribes, federal agencies, PUDs, and the Council. He highlighted the size, scale and complexity of predator management in the Columbia River Basin, saying, “I think it’s important to recognize that there isn’t a playbook, because we are writing the playbook.” One of the functions of the group is to catalog and coordinate avian predation work going on across the basin, both BPA-funded and non-BPA- funded, to identify gaps and allocate resources.

Lawonn mentioned some of the same emerging priorities as the earlier presentation, emphasizing the cormorants at the Astoria-Megler Bridge as well as additional freshwater cormorant colonies nesting on navigation markers. He also covered gull management on Miller Rocks, and increasing American white pelican foraging at fish ladders. Some overall and ongoing challenges for management include funding, scarcity of take permits, and reduced personnel at federal agencies.

Idaho Council Member Ed Schriever, acknowledging the scale of the issue, asked about next steps given the challenges with funding and implementation.

“We really need to start acting now...I think being careful, working with partners, and really taking a close look at the smaller actions we can do now and building out from that would be the answer,” answered Lawonn.  
 
Learn more: 

Avian Predation in the Columbia River Basin 2024 Annual Report 
Program Tracker- Predator Management