Oregon’s Non-Native Fish Spell Interspecies Trouble

According to a recent study by scientists at OSU, ODFW, and the U.S. Forest Service’s Pacific Northwest Research Station in Corvallis, the largest consumers of threatened salmon in Oregon are non-native, warm-water fish species.  

The study found that non-native species of warm-water fish such as walleye, bass, and crappie consume more baby salmon than native fish per individual.   

These findings will hopefully assist fishery managers in Oregon to identify the best ways to organize and plan, said Christina Murphy, lead author of the study and postdoctoral researcher at OSU.   

“We are providing the science to help managers identify tradeoffs to make the best management decisions for each individual location,” said Murphy. 

Partially thanks to this research, management actions are being taken to remove fishing restrictions on non-native warm-water fish species which are prized by many fishermen. In particular, these restrictions are being removed in areas that have an overlap of non-native fish and sensitive native species, such as salmon. 

The study also found that dams in the Willamette River and other areas formed a largely unnatural overlap between native and non-native species of fish in reservoirs. This resulted in non-native species making a large predatory impact on salmon populations, including spring chinook.   

Additionally, according to a lawsuit filed against the U.S. Army Corps of Engineers earlier this year, these dams have also blocked spawning grounds for threatened chinook salmon and winter steelhead trout, contributing further to rapid population declines. Federal judge Marco Hernandez ruled in favor of the three environmental organizations that sued the Corps, claiming that it had failed for years to maintain adequate passage for these species at the dams it operates along the Willamette Basin — and ordering them to make immediate changes. Interestingly, in a separate OSU study, genetic analyses revealed that hatchery-spawned coho salmon may also have a negative impact on wild coho salmon and their ability to reproduce.  

By combining isotope analysis and examinations of the stomach contents of non-native fish, researchers were able to shine some light on one of the Oregonian fishing world’s biggest questions: who is eating all of the salmon?  

While it’s known that sea lions make a large impact on the populations of adult salmon, it was unclear exactly what was eating the adolescent and baby salmon. The culprits? Walleye, with between 15.8-18.5% of all examined walleye having salmon in their stomachs.  

Largemouth bass, white crappie and native pikeminnow had miniscule amounts of salmon detected in their stomachs, with black crappie, cutthroat, rainbow trout and yellow bullheads not having any salmon present in their stomachs during the study.  

One co-author of the paper, Ivan Arismendi, an assistant professor with the Department of Fisheries, Wildlife, and Conservation Sciences at OSU, had more to add.  

“Our findings support this strategy of integrated management, emphasizing that the capture of popular non-native warm-water species such as walleye can be promoted in areas that are overlapping with conservation priorities for salmon,” said Arismendi.