BAKER CITY, Ore. (AP) The perch killers arrived at Phillips Reservoir under cover of night.
All 25,000 of them.
A truck emptied its cargo of juvenile tiger muskies, a sterile hybrid fish with an insatiable appetite, into the Baker County reservoir Tuesday evening.
Officials from the Oregon Department of Fish and Wildlife hope the voracious tiger muskies will end the nearly 20-year reign of yellow perch in a reservoir that used to be one of the prime rainbow trout-fishing spots in Eastern Oregon.
Since some anonymous person illegally released yellow perch in Phillips Reservoir, the number of angler visits there has plummeted by about 90 percent, said Tim Bailey, the district fish biologist at the ODFW office in La Grande.
Tiger muskies, a hybrid of the northern pike and the muskie, have helped trout populations recover in several Western lakes that, like Phillips, have been overtaken by perch or other introduced species, Bailey said.
Releasing tiger muskies isn't the first strategy the agency has employed at Phillips, which is along the Powder River about 17 miles southwest of Baker City.
For the past five springs, not including 2013, the agency used a net trap to catch several hundred thousand perch.
Trouble is, the agency estimates the reservoir's perch population at 1.5 million, Bailey said.
And studies have shown that perch procreate so prolifically that they can recover even if as much as half of the population in a particular water body is eliminated.
So long as perch is the predominant species in the reservoir, they will continue to outcompete trout for food and habitat.
"Netting has been somewhat successful but not nearly enough to restore the trout fishery, which is our goal," Bailey said.
And so ODFW now turns to the tiger muskies which, among other advantages over the net trap, are at work around the clock.
The fish were free, too they were raised at a federal hatchery near Casper, Wyo. Since fish don't do well in tanker trucks, they made the trip in a single day, which explains their late arrival Tuesday, Bailey said.
Tiger muskies are particularly ill-suited to being confined for the same reason that makes them ideal for dealing with Phillips' perch predicament:
"They start eating each other," Bailey said.
Tiger muskies don't need to grow into their aggressiveness, either they pretty much hatch with an attitude.
The bunch dumped into Phillips Tuesday are about 5 inches long, Bailey said.
"But I think they kind of believe that they're three feet long," he said. "They're bold, and will swim up to bigger fish. At this age they might be the ones that end up being the prey."
Bass, for instance, would probably enjoy a meal of adolescent tiger muskie, Bailey said.
But it's their ability to be predator, not prey, that makes tiger muskies ideal for Phillips.
Bailey expects the 5-inch fish will immediately start gorging themselves on this year's crop of perch, which are smaller.
Tiger muskies don't know the difference between a perch and a trout, of course, so there's apt to be some collateral damage.
"We're not saying the tiger muskies won't eat trout they will," Bailey said. "But it's really a numbers game."
With a million and a half perch in the reservoir, and maybe several thousand young trout, the odds are good that the tiger muskies' meals will be almost wholly perch.
Even so, the tiger muskies will need at least several years to significantly pare the perch population, Bailey said.
ODFW will release another batch of tiger muskies next year.
Depending on the results of trout and perch surveys that agency officials will conduct each year, ODFW could augment the tiger muskie population in future years as well.
Although tiger muskies won't reproduce nor does ODFW want them to, given that one non-native species, the perch, has already caused considerable trouble they can live for as many as 15 years. And given the fish can grow to 2 feet or more, a single tiger muskie can swallow quite a lot of perch in a lifetime.
What tiger muskies won't do, generally speaking, is bite a hook.
They're difficult to catch, which is a good thing, Bailey said.
For at least the first year, tiger muskies will be a catch-and-release species.
ODFW wants as many tiger muskies as possible to survive and to continue to gobble perch.
In the future the state might set up a trophy fishery whereby anglers can keep one large tiger muskie, Bailey said.
Ultimately, he said, ODFW wants to resume what was, in the pre-perch era, its standard way of managing the trout fishery in Phillips.
ODFW used to release tens of thousands of fingerling rainbows 3-inch fish each spring. Those trout grew into legal-sized fish (8 inches or longer) and reproduced.
But perch, which like to eat little trout, made that stocking strategy a waste of time and money, Bailey said.
ODFW's alternative tactic, which is still in place, is to stock only adult trout, longer than 6 inches, which are big enough to fend off the perch.
But there are far fewer trout released now about 50,000 per year.
That, combined with the predations of the perch, has drastically changed anglers' experiences at the reservoir.
Phillips used to be renowned for its rainbow trout, with fish of two pounds or more being reeled in frequently.
But over the past two decades, perch, which rarely exceed 12 inches, have become the most commonly caught fish.
Although Bailey concedes that some anglers like perch they are tasty he cites the survey, showing a 90-percent reduction in angler visits, as proof that most people prefer trout.
Information from: Baker City Herald, http://www.bakercityherald.com/
Copyright 2013 The Associated Press