Foreign species threaten salmon

GRANTS PASS, Ore. – A panel of scientists has advised letting anglers catch more shad, smallmouth bass and walleye in the Columbia and Snake rivers to help wild salmon.

The reason is that hydroelectric dams have turned the rivers into a series of lakes where nonnative fish have an advantage. Those fish eat a lot of baby salmon, compete with salmon for food and pass disease.

But the head of fisheries for the Oregon Department of Fish and Wildlife says not enough people fish for these species to make much difference.

Ed Bowles noted that there’s been a bounty on northern pike minnow, a voracious predator of young salmon, and their numbers still have not been appreciably reduced.

The Independent Science Advisory Board report said nonnative species – fish, shellfish and plants – should be treated as a significant threat to salmon, on a par with habitat loss, climate change and development from a growing human population. It identified the reservoirs behind dams as hotbeds of nonnative species, where they are better adapted to warmer and more slowly moving water than salmon.

“It has grown more clear that nonnative species are problematic and can have a negative effect on native animals, plants and ecosystems,” said Nancy Huntly, a professor of wildlife biology at Idaho State University and chairwoman of the advisory board.

Changes to salmon habitat, particularly the dams and their reservoirs, have “opened a Pandora’s box for a lot of these nonnatives to become established,” said Thomas Poe, a retired U.S. Geological Survey fisheries biologist and lead author of the report. “They act as source reservoirs that spread to other parts of the basin.”

Nonnative game fish were introduced to expand opportunities for anglers decades ago, before biologists understood the harm they caused native species. Besides bass and walleye eating young salmon, American shad – which some years outnumber salmon in the Columbia – eat the same plankton that young salmon eat and can pass on a harmful parasite.

Other nonnative species include the Asian clam, which has driven out native shellfish, and Eurasian milfoil, a plant that forms dense mats on the water’s surface, altering the ecology.

Bowles said the dams remain the No. 1 threat to Columbia salmon, slowing the migration of young fish to the ocean and making them easier targets for predators.