Beaver Creek faces invaders
East Multnomah County is being invaded by a stealthy, scaly intruder, and few people are even aware of the assault.
This is yet another fight for dominance in our waterways.
A recent bridge project in Troutdale revealed a surprising influx of non-native green sunfish. They are battling for stream habitat against endangered native salmon in the upper Beaver Creek watershed.
The extent of the incursion came to light as Multnomah County installed a new 60-foot bridge at Cochran Road, which opened Tuesday Nov. 18.
Biologists removed the fish in the water at the bridge construction zone, allowing a careful count.
They were shocked to discover 361 green sunfish, compared to only 15 juvenile coho, 3 juvenile rainbow and 27 young lamprey.
"Now we're trying to figure out what to do about it," said Steve Wise, executive director, Sandy River Watershed Council.
"I was surprised," said Roy Iwai, with Multnomah County's Water Quality Program.
He explained that the county did similar work in 2010 and 2011 "and we did not see any green sunfish" in Beaver Creek.
Only a few green sunfish were discovered in the 2017 replacement of a nearby culvert at Stark Street.
"It's striking that we did not see these fish before and now we are seeing them in large numbers," Iwai said.
Biologists think that sometime between 2010 and 2015 the green sunfish were illegally introduced in the upper tributaries of Beaver Creek, probably for mosquito control.
Ben Walczak, the district fish biologist with the Oregon Department of Fish and Wildlife, said the invasive green sunfish have been found elsewhere in the Willamette Valley.
"Generally it is from a farm pond that people have stocked with good intentions," he said, explaining that people stock the sunfish as food for bass or for mosquito control. Introducing invasive species in such cases is illegal.
Most of the green sunfish found in Beaver Creek in the recent bridge project were 2 to 3 inches long, but they can get to be about 8 inches, Iwai said.
"There will be serious competition for habitat and food between species. Sunfish and salmon species all rely on a variety of insects, worms and snails in the water. More sunfish means more competition for limited food that flows downstream," according to a blog post by Iwai.
And, as the stream warms up, it is more favorable to the green sunfish than to the salmon, which prefer colder water.
"And, with climate change, these fish (the sunfish) now can survive over the winter because the water doesn't get cold enough to kill them," ODFW's Walczak said.
"With more trees, we may help these salmon to survive," Iwai's blog post said.
The county agency and watershed council also urge private landowners to work with them on habitat restoration, which will cool the water and improve habitat for endangered salmon.
And, on the invasive problem, "the best thing for people to understand is they can't plant fish in creeks or ponds. It can cause a threat to endangered fish, as in Beaver Creek," Wise said. "There are no instant or simple solutions, unfortunately," said Wise.
Beaver Creek is key
Although Beaver Creek may not seem like important salmon habitat, "we've found that Beaver Creek is significant beyond its size and length in what it contributes to the habitat health of the Sandy Basin," Wise said.
"For a small and relatively developed creek, it is doing a big job providing good habitat and productive habitat," he added.
Beaver Creek produces between 4% and 9% of the juvenile coho salmon among the tributaries of the Sandy River Watershed.
The new $3 million bridge, at Southeast Cochran Road between Troutdale Road and Paloma Avenue, replaces a 90-year-old culvert that made it difficult for fish to migrate upstream to spawn. The Cochran Road culvert was on the state's priority list to remove barriers for fish.
A nearby culvert was also replaced at Stark Street in 2017 and Troutdale Road in 2018.
Altogether about 6 miles of salmon habitat has been improved with the culvert replacement projects.
The new Cochran Road Bridge also allows big logs to get through, an improvement over the old culvert which trapped some large debris causing problems.
Removing these two barriers restores access to upper Beaver Creek for endangered steelhead trout, coho salmon, Chinook salmon and a variety of other native fish, said Iwai.
The new bridge also has areas that removes pollutants from stormwater. A new stream channel that runs under the bridge has gravel, cobble and boulders like a natural stream.
But Iwai's blog said that "stream side revegetation is occurring at a vigorous pace through the East Multnomah Soil & Water Conservation District's stream care program."
And, although the green sunfish invasion is troubling and interesting, Iwai said he hopes "the idea of the invasive species doesn't take away from the success of the project."
You can help
The Sandy River Watershed Council is hosting a Beaver Creek restoration work party from 10 a.m. to 1 p.m. Saturday, Dec. 7, at Glenn Otto Community Park, 1102 E. Historic Columbia River Highway. Volunteers will remove non-native invasive plants along the creek to help stabilize the bank. Dress for the weather. All tools and training provided at this family-friendly event.
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