DOW decides to cull Blue Mesa lake trout

“The relationship is out of balance”

If you’re looking for a great kokanee salmon and lake trout fishery, Blue Mesa Reservoir is the place to go. The last two state-record lake trout have been pulled from the reservoir near Soap Creek, largely because of the salmon.

Soon, those days might be little more than a fond memory, however, if officials from the Colorado Division of Wildlife don’t take steps to reduce the number of small to medium-sized lake trout, also known as Mackinaw, in the reservoir.
Lake trout were first introduced into the reservoir in 1968 after bad weather forced a pilot to drop a load of fingerlings meant for Morrow Point Reservoir into Blue Mesa instead.
The DOW says average-sized lake trout are now eating more kokanee salmon than the division can replace through stocking. Those salmon are not only important to the anglers that show up to fish for them, but they feed the trophy trout as well.
So the DOW is formulating a plan to remove the average-sized lake trout from the reservoir this fall to reduce the pressure on the salmon, two to three million of which are released into the reservoir each year.
“This is a predator-prey relationship issue,” says Dan Brauch, aquatic biologist for the DOW in Gunnison. “At Blue Mesa Reservoir, the predators are overwhelming the prey; the relationship is out of balance.”
Lake trout 17 to 30 inches in length will eat around 13 pounds of kokanee salmon a year, while a larger trophy fish that can weigh more than 40 pounds will eat around 50 pounds of salmon in a year.
The over-abundance of smaller trout is putting the pinch on kokanee, whose numbers dropped from an estimated one million in 1994 to just 200,000 last year. The lake trout are also feeding on rainbow trout, which has resulted in a decreased population.
“The DOW’s strategy will be aimed at maintaining a highly productive kokanee fishery, a good rainbow trout fishery and a viable trophy lake trout fishery,” says John Alves, senior aquatic biologist for the DOW’s southwest region. “Without a strong population of kokanee salmon there is no possibility of growing lake trout to trophy size. There is room for all the species in the lake, but careful management is necessary.”
Kokanee, the land-locked form of sockeye salmon, are the fish that draw anglers to Blue Mesa. A multi-year survey by the DOW showed that 40 percent of the anglers who travel to the reservoir are going for the salmon. Even the rainbow trout draw more anglers than lake trout.
But Brauch says that doesn’t mean there is no place for lake trout.
“Lake trout angling has created increased interest at Blue Mesa Reservoir in the last decade, especially in April to May,” he says. ”We do believe that Blue Mesa can support both an abundant kokanee population and a viable trophy lake trout fishery.”
The catch of Kokanee, according to creel surveys by the DOW, has declined significantly from 175,000 caught in 1993 to just 30,000 caught in 2008.
The catch of lake trout, however, has increased substantially from about 1,700 per year during the late 1990s to about 8,600 in 2008, according to the DOW. The large increase in the catch rate indicates significant growth in the natural reproduction of lake trout.
At the same time, the size of lake trout is declining because competition for food among the fish is increasing.
Alves says this is a serious issue for Blue Mesa Reservoir, one of Colorado’s major fisheries. “We’re losing kokanee and we’re losing the potential for long-term production of trophy-sized lake trout.”
According to Brauch, “Angling at Blue Mesa Reservoir creates an estimated $8 million of angling-related economic output. The statewide kokanee program, which depends on Blue Mesa to supply about 60 percent of its kokanee egg supply annually, provides angling opportunities at many kokanee fisheries throughout the state.”
Although no final plan has been made, the DOW envisions a fall round-up when biologists will catch small to medium-sized lake trout in rubber nets between October and November, when the fish come into the shallows to spawn.
They say a specific technique will be used to minimize the injury to large fish; those fish will be released into the reservoir, for the most part, unharmed.
 The overpopulation of lake trout is causing some concern in 26 other reservoirs around the state where the division stocks kokanee salmon.
The number of fish to be removed each year will be determined based on creel [angler data] surveys and the results of spring population monitoring.
Anglers can also help with reducing the lake trout population by keeping the fish they catch. A 2008 survey showed that anglers caught 8,600 lake trout but released half of them.
“In an environment like Blue Mesa Reservoir where lake trout reproduction is significant and prolific, angler harvest of small- to medium-sized lake trout will help the DOW maintain the balance between lake trout and kokanee populations,” Alves says.
A public meeting will be held in August to discuss the removal of lake trout from Blue Mesa.
Alves says, “We’ve never removed lake trout from the reservoir, so we will plan the operation carefully and work diligently to develop the best techniques.”