DOW tries to restore Kokanee salmon at Blue Mesa Reservoir
In 2010, the Colorado Division of Wildlife targeted the removal of the Kokanee salmon’s main predator, the lake trout, in a continued effort to restore the Kokanee salmon population at Blue Mesa Reservoir near Gunnison.
Similar to what’s believed to be happening in Green Mountain Reservoir, predation by lake trout has decimated Kokanee salmon populations. At Blue Mesa, it’s been ongoing during the last decade.
The Kokanee population, once estimated at more than 1 million, has declined by nearly 75 percent since 2000. With the population now estimated to be only 270,000, anglers caught an all-time low of 23,000 Kokanee in 2010, just 18 percent of the landings in 2000.
To reduce Kokanee predation in the area, biologists have targeted primarily the segment of the lake trout population that is most numerous – fish less than 30 inches.
At Blue Mesa in 2010, about 1,733 lake trout were removed from the reservoir, roughly double the number removed in the previous year. The fish that were removed were filleted, frozen and distributed to licensed anglers in the Gunnison area.
The lake trout population has grown significantly in Blue Mesa during the last decade, which has precipitated the decline in Kokanee. Based on monitoring results completed last spring, biologists estimate that since the early 2000s the number of lake trout less than 20 inches has increased by 570 percent. During the same period, the number of lake trout more than 30 inches caught during sampling surveys has increased by 70 percent.
Paring back the burgeoning population of smaller lake trout is also necessary to maintain enough forage to sustain trophy-sized lake trout at Blue Mesa.
In recent years, the Division has attempted to increase the harvest of lake trout by increasing bag and possession limits -they are now unlimited for lake trout under 38 inches – and by encouraging fishermen to take more fish home. But anglers are not harvesting enough fish to keep up with population growth; some are also releasing lake trout back to the reservoir.
Native to Canada and the upper Midwest, introduced lake trout are also causing problems in other lakes and reservoirs throughout the West. Stocked illegally into Yellowstone Lake in Yellowstone National Park, lake trout are decimating native Yellowstone cutthroat trout, which provide a critical food source for the park’s grizzlies. In Montana’s Flathead Lake, lake trout are punishing the population of native bull trout, a threatened species, and have nearly wiped out the stocked Kokanee salmon population. Lake trout are also harming sport fisheries in Washington, California, Idaho and Wyoming.
– Daily News staff report
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