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Prowling tigers

At Diamond Lake, the discovery of a single tui chub last October has the Oregon Department of Fish and Wildlife ready to go all-in to keep the chub's last ugly invasion from repeating itself.

The agency is using trap nets and buzzing the shallows with electroshocking gear to see whether any more chub exist in the lake and to kill them now before waiting the 13 years it took the last time for one chub to turn into almost 100 million.

It is also adding to the mix some bad-ass, marauding franken-fish called tiger trout — a hired gun of sorts — that biologists hope will lay in the weeds and attack any chub they might find — if there are any more.

"We thought, let's plan for the worst and hope for the best," says Greg Huchko, ODFW's Umpqua District fish biologist. "I don't want to wait around until there's millions of them."

Biologists have unleashed tiger trout at Fish Lake, as well, but for a slightly different reason.

Fish Lake sports anywhere from 400,000 to 500,000 illegally introduced tui chub. While a 2006 rotenone treatment at Diamond Lake wiped out the chub there, repeated treatments at Fish Lake have failed to kill off the chub, which likely take refuge in the lake's many springs.

Tiger trout stocked at Fish Lake Friday are expected to feast on chub, but they're not expected to keep the chub population in check. Rather, biologists hope the 24-hour buffet of chub will help to grow a population of a big, fat and rather ugly fish for anglers to target.

"We're trying to take advantage of the chub and hopefully grow a nice fish for anglers," says Dan VanDyke, Huchko's ODFW counterpart in Central Point. "When it comes to tui chub, it's one of the only weapons we have."

So whether tiger trout are added to be hooligans or gluttons, it's time for Southern Oregon anglers to get to know the tiger.

Tiger trout are the sterile offspring of a female brown trout and a male brook trout. They get their name from the black vertical stripes that look like nothing else in the trout world.

They are rarely found in the wild, but they have been discovered occasionally in the upper Midwest where brook trout and brown trout spawning grounds overlap. In hatcheries, they take a bucket full of brown trout eggs and dump in some brookie milt, and hatchery workers can easily get a 85-percent survival rate.

Tigers are considered a good hybrid in these cases because they pose great danger to the chub and little danger to the rest of the piscatorial world.

The bad-ass part of them is that they are fearless hunters, very willing to fin in the shallow weeds where tui chub set up shop. If tigers escape, they're not expected to damage downstream habitat or turn into an invasive species because of their sterility.

The 18,000 four-inch tigers stocked last week at Diamond Lake cost $20,000 to purchase and transport from the same private Utah hatchery that released another 1,500 tigers Friday at Fish Lake.

This marks the fifth tiger trout-stocking in six years at Fish Lake, totaling about 31,000 tigers, VanDyke says. So far, the biggest tiger caught in fall gillnet surveys is 16 inches, he says.

Any caught tiger must be released unharmed, and anglers are apparently so good at it that only one picture of a Fish Lake tiger has been sent to the ODFW office by an angler, VanDyke says.

"All we know is we're getting some big tiger trout showing up in gillnets, but we aren't getting a lot of sightings," VanDyke says.

While the verdict is still out on tiger trout's success at fulfilling their angling promise at Fish Lake, the story is equally vague at Diamond Lake.

Several case studies on tiger trout, primarily out of Utah, show a mixed bag on their abilities to beat back invasive species like chub. 

"In some lakes they work fantastic, and other lakes not so much," Huchko says. "We'll see how they do. I'm optimistic."

Reach Mail Tribune reporter Mark Freeman at 541-776-4470 or mfreeman@mailtribune.com. Follow him on Twitter at www.twitter.com/MTwriterFreeman.

A tiger trout gets its bearings after being released Friday into Fish Lake. Mail Tribune / Jamie Lusch