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FLAMING GORGE - Managing the fishery of a massive reservoir with myriad species can be daunting. Every angler, interest group and guide has different expectations and advice on how to make things work.

While the arrival of a tasty and relatively easy-to-catch species may seem like a good thing, the voracious, eellike predator appears to be wreaking havoc on the complex web of life that is Flaming Gorge fishery.

Burbot, or ling cod, have found their way into the 91-mile-long reservoir that straddles the Utah/Wyoming border and are taking advantage of a seemingly endless food supply without much risk of getting eaten themselves.

"All the indications are there that the population could explode, even more than it already has," said Robb Keith, a Wyoming Game and fish regional fisheries supervisor for the Green River Region. "They are just plowing their way through the reservoir and eating anything they can find."

To figure out just how fast the burbot population is growing and the impact it is having on the other species in the Gorge, biologists have asked researchers at Utah State University in Logan to conduct a study.

The team started its research in January, collecting burbot for various lab tests. Burbot were collected again in the early spring. The two-year study also will include summer and fall sampling.

"The population is expanding tremendously," said Chris Luecke, head of the Department of Watershed Sciences at USU. "So far, we can say that some 7-year-old burbot have shown up and that they are mostly eating crayfish."

Of utmost concern is the precarious population of kokanee salmon in Flaming Gorge. The landlocked salmon are not only one of the most popular species among anglers, but a vital part of the diet of the reservoir's world-class trophy lake trout fishery.

The salmon population in the Gorge is traditionally cyclical, with two years of strong numbers followed by a couple of lean years before the numbers rebound.

"The [kokanee] population has been flatlined for about five years now. That could be too much predation from lake trout, which are abundant, or it could be from poor spawning," said Lowell Marthe, the Green River/Flaming Gorge Project leader for the Utah Division of Wildlife Resources.

Poor spawning could be due directly to burbot feasting on kokanee eggs during the spawn, again when the salmon fry are emerging in the spring.

Keith isn't ready to place all the blame for the kokanee doldrums on burbot, noting there can be other factors. But he does acknowledge that a direct impact can't be far off.

"We have had scuba divers tell us they observed burbot among the kokanee while they were spawning eating the eggs. We have found 2-year-old kokanee in the bellies of 18- to 26-inch burbot," Keith said. "The whole management of the reservoir for the last decade or more has been on kokanee, recognizing they drive the lake trout fishery. We have tried to manipulate those two species to keep everything in balance. That is what is in jeopardy."

The problem is magnified by the fact that kokanee and rainbow trout have a life span of 4 years - with some rainbows living a little longer. The fish feeding on those two species are long-lived predators that will consume thousands of salmon and trout over the course of their lives.

To boost the natural kokanee population in the reservoir, fisheries officials are trying to plant more hatchery salmon. They were lucky enough to secure 1.2 million kokanee in 2007 - usually only 700,000 to 800,000 are available.

"The eventual plan is to stock 2 million kokanee per year," Marthe said.

The problem with increasing the number of kokanee produced in a hatchery is that fewer rainbow trout can be produced there to stock the Gorge.

Kokanee and rainbows for Flaming Gorge are provided by Jones Hole National Fish Hatchery between Vernal and the Gorge. Marthe hopes that as the production capacity of Utah's hatcheries increases with ongoing improvements, the states could take on rainbow production and leave kokanee stocking to workers at Jones Hole.

"Kokanee are the keystone species, so many other things rely on them," Marthe said. "They are such a popular fish at the Gorge it would be a shame to see the opportunity go away, which it very well could."

No one knows if burbot naturally made their way into the Gorge down the Green or if they were stocked directly into the reservoir. Either way, it was an illegal introduction in the Green River drainage that will affect anglers in a variety of ways.

In such a large reservoir with a huge biomass of fish, about the only control biologists have is through anglers. Biologists from both states say a continued focus on keeping juvenile lake trout can help protect the kokanee. They also encourage anglers to give burbot fishing a try. Anglers should also keep in mind that all burbot caught must be killed in Utah.

The best-case scenario at the Gorge is that the burbot population stops growing exponentially and that lake trout, and even smallmouth bass, turn more of their attention to burbot as a food source.

"In some Alaska lakes we work on, the lake trout seem to control burbot," Luecke said. "That doesn't seem to be happening at Flaming Gorge."

At some point, burbot should start taking a bite out of their own population. That is something the first-year burbot didn't have to contend with, but young burbot already have been found in the stomachs of older fish.

Nature is the most likely to bring balance.

"If we can't get enough angling pressure on burbot and lake trout, that's what it comes down to," Marthe said. "In all reality it will be up to the fish to decide who is king of the mountain and at least even things up."

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* BRETT PRETTYMAN can be contacted at brettp@ sltrib.com or 801-257-8902. Send comments about this story to livingeditor@sltrib.com.

Flaming Gorge Fish

Lake trout

These large nonnative trout drifted down the Green River from its headwaters in the Wind River Mountains of Wyoming and eventually became the No. 1 predatory game fish at Flaming Gorge. The population of Utah chub, the main forage fish in the reservoir, were all but eliminated and the hungry lake trout turned to other food sources like kokanee salmon and rainbow trout. Utah biologists hope the lakers turn some of their dining habits to burbot.

Kokanee salmon

These landlocked sockeye salmon were introduced by wildlife officials in the mid-1960s. The salmon established a naturally reproducing population and eventually became a favorite species for anglers on Flaming Gorge. Today the kokanee population is precarious: they have become the main food source for lake trout. Increasing predation by burbot could be too much for the kokanee. Officials will attempt to increase the number of kokanee in the reservoir by augmenting natural populations through stocking.

Smallmouth bass

Smallmouth and largemouth bass were introduced in the 1960s to help control Utah chub numbers. The largemouth never caught on, but the smallmouth can be found throughout the 91-mile reservoir. Smallmouth rely heavily on crayfish as a food source. Burbot are feasting on crayfish. The impact on smallmouth is not known at this time.

Burbot

Anglers started catching burbot through the ice on the north end of Flaming Gorge in the winter of 2003-04. Burbot, a member of the cod family, are native on the east side of the Continental Divide in Wyoming, but are considered an invasive species on the west side. The burbot population is exploding in the Gorge with fish being documented at least four miles into the Utah side of the reservoir. The voracious predators are eating everything in sight, raising concerns about the impact on the entire Flaming Gorge fishery.

Rainbow trout

Rainbow trout are the most sought after of the game fish at Flaming Gorge. There is little, if any, natural reproduction in the reservoir. Biologists stock 450,000 8-inch rainbows each year. Anglers take the majority of rainbows from the reservoir, but lake trout and burbot also feed on the planted fish. Officials hope to plant up to 1 million rainbows annually in the coming years.

Other species:

Other sport fish in Flaming Gorge include channel catfish, brown trout and crayfish. Nongame species include carp, white suckers and Utah chub.