October 29, 2004

In order to protect kokanee salmon populations, the Colorado Wildlife Commission has changed fishing regulations at Blue Mesa Reservoir. The new regulations allow for the unlimited take of yellow perch beginning on Nov. 1.

Perch were illegally introduced into the reservoir during the 1990s, and the illegal introduction threatens kokanee salmon populations through competition for food sources and increased predation on young fish.

"Kokanee have a very limited diet," said Dan Brauch, a Colorado Division of Wildlife (DOW) Gunnison area aquatic biologist. "They depend on a good supply of water fleas (Daphnia). Perch also consume the water fleas in large numbers, so they threaten to strip the zooplankton prey base of the kokanee."

Beyond the threat to kokanee, biologists believe the illegal introduction of yellow perch may eventually have a negative impact on Blue Mesa's lake trout (Mackinaw) populations.

"An illegal species introduction throws everything in an ecosystem out of balance," said DOW aquatic researcher Pat Martinez.

Currently the DOW manages lake trout as a predator species and kokanee as a prey species in the reservoir. Adding another predator species to the reservoir has the potential to cause problems for all of the aquatic life.

"Currently, Blue Mesa is one of the best kokanee fisheries around," said Martinez, "and it produces some of the largest trophy lake trout in the lower 48 states. A lot of hard work goes into balancing this very delicate food web and the illicit introduction jeopardizes that work."

Lake trout thrive in Blue Mesa in part because they get high caloric intake from preying on kokanee. If perch replace kokanee as the dominant prey species, the body mass of the lake trout is likely to decline. With fewer kokanee and poorer quality lake trout, Blue Mesa runs the risk of losing its place as a top fishery.

DOW biologists also worry that damage to kokanee populations at Blue Mesa could spell the loss of kokanee fishing at lakes and reservoirs around the state. The Blue Mesa kokanee spawning run generates the state's largest supply of eggs and milt for raising kokanee in hatcheries.

DOW species surveys of the reservoir indicate that now is the time to act to reduce or eliminate yellow perch.

"We're definitely seeing more perch caught in Blue Mesa," Brauch said. "Our creel surveys indicate that the species has moved from rare to common.

DOW personnel randomly interview anglers to gain biological information. A creel survey involves asking the fisherman about what species they are fishing for, what they are catching, what kind of bait or lure is being used, and what length of time they have been fishing on that given day. Creel surveys may also include measuring and examining any fish caught.

Blue Mesa isn't the only body of water in Colorado facing significant challenges from illegal stocking or dumping of fish. The DOW continually tracks more than 65 illegally introduced populations around the state. Because of this on-going problem, the DOW would like to remind everyone that transporting live fish or releasing fish and other aquatic wildlife into Colorado ponds, streams, and lakes is illegal without proper licenses and permits.

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