Oregon Battles Invasive Minnows To Protect Non-Native Trout

It’s been an unseasonably warm June week at Oregon’s Diamond Lake.

This makes for some lovely fishing weather, but it’s not ideal for fish stocking. And that’s what a small group of employees with the Oregon Department of Fish and Wildlife are here for.

“As soon as Greg gives me the word, I’ll dump ‘em in,” says the fish deliveryman.

The thousands of fish traveled via small trailer through the night from a hatchery in Utah. The driver arrived about two hours early in an attempt to beat the heat.

ODFW’s Greg Huchko consults with a coworker who’s taking the water temperature at the boat landing — it’s about 65 degrees. The water in the hatchery tank is 56. It’s just within the 10-degree difference limit the biologists will allow to ensure the fish don’t experience too much shock when they enter the water.

“I say go for it whenever you’re ready,” Huchko calls out over the chatter of about ten fishermen who’ve gathered to watch.

The hatchery man pulls the plug on the tank, and in a gushing roar, 5000 tiger trout shoot out of a pipe and into the clear water.

This is just the latest non-native fish to be introduced into Diamond Lake.

Frustrating history

Southern Oregon’s Diamond Lake has a long and frustrating history. It’s alternated between begin one of the best trout fishing spots in the Pacific Northwest to being overrun with an invasive bait fish called the tui chub.

Twice now, the chub have moved in, caused toxic algae blooms and pushed out sport fish. Both times, state wildlife officials have taken the extreme and expensive measure of poisoning the entire lake. This last happened just 10 years ago.

But now the tui chub have appeared again. Wildlife officials found one last fall, and dozens more in traps in early June.

No one knows exactly how the fish were introduced, but there is a leading theory.

“Some idiot again, I guess, brought in some more live, little baitfish,” says fisherman Don Currey, who watches the tiger trout slipping into pollen-coated lake.

Using live bait in Diamond Lake is illegal and the consequences have proven to be devastating.

Currey’s been fishing this lake since the 1970s. He saw what the tui chub did to the rainbow trout fishery and doesn’t want the population to explode yet again.

This morning, Currey and his wife are putting in their  drift boat and going for trophy rainbow trout – with worms, he assures.

“I don’t think there’s as [many] as there used to be, but there will be,” he says of the invasive minnow.

Chub problems

Tui chub love Diamond Lake.

Lomolo Lake, just a few miles downstream, has chub, too. But they haven’t taken over like they have previously in Diamond Lake – and exactly why is a mystery.

Huchko says part of it probably has to do with the depth of Diamond Lake. It’s shallow – averaging about 25 feet.

“The temperatures along the shoreline warm up pretty well because of that. And it really leads to a proliferation of tui chub. They can populate pretty rapidly,” Huchko says.

One reason that Diamond Lake is considered to be such an amazing trout fishery is the sheer amount of benthic invertebrates, or trout food, in the water. Without chub, the lake boasts more than 300 pounds of this larvae and insects per acre. The stocked rainbow trout grow about 1 to 1.5 inches per month – small fish become large enough to spare fishermen from lying about the size of the ones they reel in.

But when the tui chub take off, they eat up all the trout food.

“Really what happens is they become the top predator in the lake,” Huchko says.

After just a few years, the population of zooplankton falls off a cliff.

“We can go from that 300, 350 pounds per acre down to almost zero,” Huchko says. “And at that point the ecology of the lake essentially collapses.”

 Watch Oregon Field Guide's Restoring Diamond Lake:

Without the zooplankton, Diamond Lake experiences massive blooms of toxic blue-green algae. The trout numbers drop. The shorelines become clogged with green sludge and the water becomes dangerous for humans and animals to touch.

People stop coming to Diamond Lake.

This all happened back in the early 2000s, and now history could be repeating itself.

Next shiny nickel

To keep this from happening, the Oregon Department of Fish and Wildlife are deploying a swimming stomach called a tiger trout.

Tiger trout are like mules  — a cross between a brook and brown trout. This cross-breeding occasionally happens in the wild, but not often. And the fish that are produced are sterile.

Recently hatchery operators across the West have started to breed tiger trout as a sport fish and as a biological control for managing unwanted fish populations.

Because they can’t produce offspring, they’re particularly attractive. They don’t pose the risk of becoming invasive and all the energy they would usually devote to reproduction goes to growth instead.

“They’re more aggressive,” says Andrew Nikirk. “They put down the groceries, so they grow fast.”

Nikirk, a fisheries biologist with the Wyoming Department of Game and Fish, calls tiger trout the “next shiny nickel” for wildlife managers.  It's a fad he hopes will make a difference.

Nikirk’s using tiger trout in a remote lake to eat down an overpopulation of brook trout. He’s gotten anecdotal reports from anglers that fish size in the lake is increasing (evidence of success), but won’t know for sure the effectiveness of the tigers until they take samples this summer.

“The good thing, if it works, you have another fish to fish for,” Nikirk says.

Anglers in Oregon’s Diamond Lake won’t have that option – at least at first. Fishermen will be required to release any tiger trout they catch so the fish have a chance to do their job.

And early signs that they will live up to their reputation are positive. Almost immediately upon hitting the water at the Diamond Lake boat landing, the 6-inch tiger trout start hitting the water’s surface, hungry for caddis flies and other insects.

When they put on a bit more size, they should start eating small fish. Huchko acknowledges this includes the prized rainbow trout fry the state stocks by the thousand each year. But in comparison, he says, the tui chub should be easier prey.

Invasives eating invasives

It's a lot of pressure to put on a few thousand hungry trout, considering the consequence of another tui chub invasion.

ODFW says the sport fishery at Diamond Lake has generated about $15 million in economic activity since recovering from the last tui chub invasion in 2006. Then, the state poisoned the entire lake, killing an estimated 90 million chub. It cost taxpayers about $5 million dollars.

At the time, poisoning the lake with rotenone wasn't popular with environmental groups. Part of the poisoning process threatened wetlands and the groups didn't like that the rotenone indiscriminately killed nearly everything in the lake, not just the chub.

In an appeal of the 2006 poisoning plan, Umpqua Watersheds, Oregon Natural Resources Council (now Oregon Wild) and Cascadia Wildlands Project also complained that taking such an extreme tactic wouldn’t likely fix the problem in the long term.

At the time, and now, environmental groups support using non-chemical measures to control the chub – including predatory fish and manual trapping.   This is the tactic that ODFW is deploying with the tiger trout. The agency has also hired two seasonal workers to trap and remove the chub, while monitoring for any population growth.

Alan Bunce of Umpqua Watersheds says he doesn't necessarily disagree with ODWF's decision to spend more money to control the tui chub. The Douglas County native grew up fishing at Diamond Lake, and saw the fishery crash when the chub expanded before.

But he says it does raise question about the state’s broader wildlife priorities.

“We have a lot of problems in Umpqua River Basin. We have lamprey, salmon, steelhead, native species that are falling off the map – really to be honest, are going extinct,” he says. “So I look at it from that standpoint: what’s the best use of public dollars?”

Bunce wants more focus on native fish restoration.  And since Diamond Lake is naturally fish-free, any fish – from the prized rainbow trout to the tui chub to the tiger trout - are technically non-native.

“In the case of Diamond Lake, we’re spending money on invasives fighting invasives fighting invasives,” he says.

This artificiality of the Diamond Lake fishery should give everyone pause, according to Joey Tuminello, a doctoral candidate specializing in the philosophy of invasive species at the University of North Texas.

“Regardless of what the right thing to do might be, he says, "it’s important to recognize we’re trying to maintain this sort of circumstance that is totally human motivated.”