Nonnative Fish Impact Western Rivers

November 19, 2007

Release from: Kyle Odegard
Corvalis Gazette-Times (Oregon)

About 20 percent of Oregon’s river and stream miles contain nonnative fish and amphibians, and that’s negatively affecting local species, according to a study by Oregon State University and U.S. Environmental Protection Agency scientists.

Amazingly, the study’s findings could almost be considered good news for Oregon.

The four-year study sampled 1,300 spots in 12 Western states, and estimated that more than half of the river and stream miles contained nonnative species. In Arizona, Colorado and Montana, the rate was more than 80 percent.

Oregon and Washington ranked lowest, with about 20 percent of waterway miles having nonnatives.

“I don’t know whether (Oregonians) can breathe a sigh of relief,” said Thom Whittier, a faculty research assistant in the OSU department of fisheries and wildlife. He mentioned how smallmouth bass populations, once prevalent only near Portland, spread further upstream in the Willamette River every year, and now are established near Albany.

“They’re a fish-eating fish, and they are likely to eat juvenile salmon,” he explained.

“It’s one more factor out there that’s a human-caused disturbance on those natural ecosystems, in addition to pollution-type impacts that are out there,” said Gregg Lomnicky, a scientist with the Dynamac Corp., which contracted with the EPA for portions of the research.

“You never know what species loss will trigger a domino effect on an ecosystem,” said Bob Hughes, an OSU senior research professor. “How many rivets can you remove from the wing of an airplane and still have it fly?”

Whittier said Oregon’s lower rate was partly a result of geography. “Fewer of the nonnatives live in higher elevation, smaller streams, and we have a lot of those,” he said.

The slower-moving waters of the Willamette River, however, are home to such nonnative species as largemouth bass, smallmouth bass, carp, yellow perch and even goldfish, Lomnicky said.

Unlike Arizona, where eight of the 12 most common fish are nonnative, the Willamette is dominated by local species such as trout and suckerfish. Five Willamette River sites or tributaries were part of the study.

The smallmouth bass, however, now may be the top species in the Umpqua and John Day rivers, Hughes said.

Some people don’t believe bass and other fish are a problem, because they add another opportunity for local anglers, Whittier said.

A large portion of the nonnative species actually were brought from the Midwest and introduced by state wildlife agencies seeking to improve fishing in the West, he said.

“Some of the new ones just starting to show up are aquarium fish,” he added.

Fishermen using live bait also can introduce species to waterways.

Whittier said nonnative fish in streams could potentially impact the surrounding food chain. If a certain fish decimates insect populations that emerge from a waterway, that could potentially reduce food for birds and bats.

Researchers studied sections of waterways by stunning fish and other critters with electricity. The fish were collected with nets, identified, checked for disease and other issues and measured. The vast majority were successfully introduced back into the rivers and streams where they were collected, Lomnicky said.