At Howard Prairie reservoir in Southern Oregon, there once was a robust rainbow trout fishery.
“They grew really well and the trout fishery absolutely thrived,” said District Fish Biologist Dan Van Dyke, about the 350,000 rainbow trout released into the reservoir each spring.
Then, about 2005, fishing in the reservoir, located just 18 miles east of Ashland, crashed.
The culprit was the illegal introduction of a surprisingly large list of invader fish: golden shiners, brown bullhead, black crappie, and both largemouth and smallmouth bass.
It’s a story that’s been repeated throughout Oregon for decades, when carefully managed fisheries of native or stocked fish are greatly damaged because of illegal introductions.
In these cases, individuals dump leftover live bait, possibly not realizing the harm. Others purposely add a different breed of fish in an attempt to alter the fishing grounds. Some also abandon fish and other sea life from a home aquarium or school project.
Once these other species proliferate, the invader fish can out-compete the native fish or trout for food. They also can stir up sediment, degrading water quality.
To fix this problem, sometimes referred to as “bucket biology,” ODFW biologists statewide are trying a wide variety of creative counter-measures that work to eliminate or reduce these illegally introduced fish in Oregon ponds, lakes, rivers and streams.
One of those options is rearing fish for a longer time in the hatchery, so that those released aren’t as vulnerable to predation.
That’s the current solution at Howard Prairie.
Previously, they released 2- or 3-inch fish in late May, Van Dyke said. But in 2010, they began raising and feeding the fish longer, releasing 6- to 7-inch fish each October, a size meant to be just larger than the smallmouth bass could feed on.
“We’re releasing fewer but larger fish at a size and time of the year when they’re less likely to be eaten by the illegally introduced bass,” Van Dyke said.
It’s helping, but the downside is that it’s much more expensive to keep hatchery fish for longer.
“Just in trout food for Howard Prairie reservoir alone,” ODFW spends about $3,700 more per year to raise 100,000 larger fish, $6,700 more per year for 150,000 fish, Van Dyke said.
Predator fish, trap nets
In the La Grande District in Baker County, the department is taking a similar approach with Phillips Reservoir, releasing larger fish instead of fingerlings because of problems resulting from the illegal introduction of yellow perch.
Here, they’ve tried some other options, too. From 2009 to 2013, for example, they removed 1.4 million perch from the reservoir using trap nets.
Wanting a more long-term solution, in 2013, they began introducing a non-native, sterile predator fish – tiger muskie – to control the perch population, estimated to be about 500,000 fish strong, said District Fish Biologist Tim Bailey.
“They would reduce the biomass of perch enough that the trout could increase in survival and growth,” Bailey said. “And that’s happened at other locations across the west.”
This year, they’re tweaking the approach with a plan to release tiger muskie that are about 10 inches long, instead of five inches. The smaller fish were surface-oriented and too susceptible to birds, making their impact on perch populations not as great as intended.
“It’s like anything new,” Bailey said. “There’s been a little bit of a bump in the road.”
Oregon’s waterways are so variable that there is no one solution for every lake or stream. In some cases, netting fish won’t work because the illegal fish are too prolific for the manpower required. In other places, chemical treatments, such as rotenone, aren’t a choice because fresh water feeds into the waterbody, leaving hideouts for fish until the chemical dissipates. Predator fish also won’t work in every case.
When rotenone is considered a good option for a lake, using it can be an opportunity to clear out all the illegally introduced fish and restart a fishery.
The cost of treating Oregon waterbodies with rotenone, using R&E program dollars, was about $800,000 for the time period between 2011 and 2015, said STEP and R&E program coordinator Kevin Herkamp. Additional federally funded stream treatments were also completed during this time period.
Add that to the food cost of raising larger trout, the expense of purchasing hatchery-raised predator fish and the staff hours and fuel spent on netting and removing invasive fish, and the problem of illegal introductions is very expensive.
Rotenone can be a successful and efficient tool, said Erik Moberly, assistant district fish biologist based in Bend. It has been used worldwide as a management tool to remove illegally introduced fish species, he added.
Moberly’s office treated North Twin lake in Deschutes County successfully last November to remove illegally introduced brown bullhead that had been increasingly competing with rainbow trout since the mid-1990s.
A deep-freeze delayed dissipation of the chemical, but Moberly thinks the new trout will thrive now as they have at South Twin Lake, which was treated five years ago for the same problem.
“What we’re seeing five years later is some really nice, healthy rainbow trout in South Twin,” Moberly said. At North Twin, “it was the right time to use rotenone and reset that lake and bring it back to a robust rainbow trout fishery.”
One of the costliest, and highest profile, illegal introduction sites was at Diamond Lake.
Here, Tui chub were competing with rainbow trout for food, deteriorating the water quality and causing problems with bacteria and toxic algae bloom that were interfering with recreation.
To fix this, at a cost of $5.5 million, in 2006, the department drained the lake to about 75 percent of its normal capacity. They treated with rotenone in the lake using pontoon boats, in boats near the shoreline using long-range sprayers and on foot using sprayers to target weedy and marshy areas near the shorelines. They also used drip stations in major tributaries, and used sentinel fish in buckets in the lake to test effectiveness at different depths and locations.
“We went through a litany of different tests to make sure that we were treating at the proper level,” said Greg Huchko, district fish biologist for the Umpqua District.
The project was successful, though Tui chub have since been re-introduced. Staff are actively monitoring the situation, and trying other alternatives to rotenone while the problem remains small.
The most effective treatment for illegal introduction long-term is prevention, which could include educating people about the effects of illegal introductions and encouraging the public to turn in the offenders.
Illegal introductions hurt fishing sales and the local economy, and they take money that could have been used for other fishing improvements, said Kyle Bratcher, assistant district fish biologist in Enterprise.
Bratcher led a rotenone project last year in 10 small waterbodies in Baker, Union and Wallowa counties. At Kinney Lake, brown bullhead catfish had so overpopulated the pond after a decades-old illegal introduction that they were not only affecting trout size. The catfish, too, had stunted growth in the overcrowded lake.
“It’s kind of a double-whammy,” Bratcher said, “because we’re spending money trying to solve this problem that we’d rather have not had to solve in the first place.”
Note: This story is the second in a three-part series looking at the issue of illegal introductions, or “bucket biology.” A previous story highlighted the many issues caused by illegal introduction. An upcoming story will discuss enforcement and prevention of this issue in the future for Oregon’s waterways.