Food Web

PRESSURE: Decreased Food Availability

Salmon need food, and those food sources are increasingly at risk. Young salmon eat insects and other tiny animals. As they grow larger, they transition to eating shrimp-like creatures (called krill), squid, and forage fish. These food sources have declined because of harvest, habitat destruction, and poor ocean conditions. Forage fish populations in Puget Sound have been particularly impacted by shoreline armoring, which reduces their spawning habitat.

Salmon are highly regarded by animals great and small, notably humans and Southern Resident orcas.

PRESSURE: Increased Predation

Salmon are nutritious and delicious, and therefore highly regarded by animals great and small, notably humans and Southern Resident orcas. They bring ocean-derived nutrients to otherwise nutrient-poor streams and forests, feeding organisms from bacteria to bears. But this tremendous service salmon provide has a downside: when ecological systems are altered by humans, salmon become more vulnerable to certain predators.

Rebounding populations of marine mammals, combined with human-made changes to the environment, has resulted in tremendous predation pressure on salmon. Between 1970 and 2015, seals and sea lions increased the amount of adult Chinook salmon they ate from 75 tons to 718 tons–double that of resident killer whales and six times more than the combined commercial and recreational catches.³⁶ Emerging science suggests that harbor seals inflict heavy tolls on juvenile salmon in Puget Sound and Hood Canal, especially in years when other species preferred by seals, such as herring and anchovies, are scarce.³⁷

Similarly, changes in river conditions caused by dams have allowed native and non-native fish and birds to eat more juvenile salmon. About 35 percent of the juvenile spring Chinook salmon from the upper Columbia River migrating to the ocean are consumed by birds, while predatory fish eat millions more in the Columbia and Snake Rivers.³⁸

PROGRESS AND PRIORITIES

Tribe and state salmon co-managers in Washington and Oregon have secured federal permits and started removing sea lions that habitually gather at bottlenecks for salmon such as Bonneville Dam, which should reduce the number of salmon eaten.

The U.S. Army Corps of Engineers manages extensive programs to reduce rates of predation by birds in the Columbia River estuary and the middle Columbia River. A bounty program that pays recreational fishers to capture pikeminnow is credited with significantly reducing the number of salmon eaten by pikeminnow.

In the marine environment, researchers are working to identify bottlenecks where juvenile salmon are being eaten in large numbers, such as the Hood Canal Bridge. Once these bottlenecks are identified, engineering solutions may ease salmon passage and reduce attractiveness to harbor seals and birds.

While progress on forage fish research and restoration in Puget Sound has been slow, the reduced pace of shoreline armoring and increased attention to forage fish habitat is encouraging.

Northern pikeminnow, above, a fish native to Washington, has quickly adapted to dammed rivers, increasing the number of juvenile salmon they are able to eat.

Banner photograph of Cormorants by Fazlul Alam

Northern pikeminnow by the Jim-Souders, Washington Department of Fish and Wildlife

Orca photograph by Candice Emmons, NOAA

Caspian tern and sea lion by Ingrid Taylor, NOAA