Washington will need to lethally remove seals and sea lions and watch what happens to learn how much the pinnipeds are harming salmon, according to a report prepared for legislators.

The Washington State Academy of Sciences reports that Steller sea lions, California sea lions and harbor seals are likely impeding salmon recovery.

Pinpointing the impact will take more research, according to the academy. “Strategic lethal removal of pinnipeds is an approach that may be required,” the report states.

Sea lions and seals are abundant, but salmon are not, so the risk of doing nothing is greater than the risk of removing pinnipeds, according to the report.

“The major risks of lethal removals appear largely social and political rather than risks to pinniped populations as a whole,” the report states.

The Legislature asked scientists to study the connection between a growing population of federally protected marine mammals and declining salmon runs.

Save Family Farming, an advocacy group, has drawn attention to the issue, arguing that farmers are under increasing pressure to give up land for salmon recovery, while the role of predatory mammals has gone unaddressed.

The federal Marine Mammal Protection Act of 1972 has been “spectacularly successful,” according to the academy of sciences, a nonprofit group that advises the state.

Pinniped numbers have grown off the coast and in inland waters, such as Puget Sound, Hood Canal, and Strait of Juan de Fuca.

Meanwhile, salmon runs have declined, but it’s unclear whether the sea lions and seals are the main hurdle to salmon recovery, according to the report.

Pinnipeds eat a lot of salmon, but they also eat fish that prey on salmon. It’s impossible to confidently predict how reducing the pinniped population would impact salmon, scientists said.

Answering the question will require “carefully constructed lethal removals” and monitoring, preferably over several years, according to the report. “Other approaches are unlikely to lead to fundamentally new insights.”

The federal act limits lethal removal of marine mammals. States can seek permission to kill individual marine mammals caught eating federally protected fish. Identifying and removing the offending individual is challenging, according to the report.

Meaningful state management is unlikely without changes to the act, scientists said.

The status quo, however, could further depress salmon populations, they said.

Scientists from the University of Washington, Western Washington, University of British Columbia, Makah Tribe, Puget Sound Institute, and the National Oceanic and Atmospheric Administration participated in the study.