Colorado Parks and Wildlife biologists continue to work aggressively to restore the kokanee salmon population at Blue Mesa Reservoir, but much more needs to be done before the fishery is considered to be in balance again.
Sonar surveys of the reservoir estimate that the current kokanee population is about 280,000, unchanged from the previous two years.
In 2001, the reservoir held an estimated 1 million kokanee. But due to predation by the rapidly growing lake trout population, the number of kokanee plummeted to about 110,000 in 2009.
"We've made some progress since then, but restoring the balance to the Blue Mesa fishery is a long-term project; our work will continue," said John Alves, senior aquatic biologist for the southwest region for Colorado Parks and Wildlife. "It's especially important for anglers to continue catching and keeping lake trout."
Since 2009, the agency has been removing lake trout from Blue Mesa and increasing the number of kokanee fingerlings stocked every spring.
Lake trout have been in the reservoir since the late 1960s, but changes in how water is stored led to a rapid increase of the species in the last 20 years. Because less water is released in the winter compared with previous years, more area for spawning and development of eggs is available to the lake trout.
Colorado Parks and Wildlife has focused extra effort on Blue Mesa because it is the most important kokanee fishery in the state. The reservoir is ideal for production of aquatic food sources; consequently Blue Mesa is ideal for maintaining a large population of salmon. In turn, the kokanee provide the vast majority of the eggs needed to stock up to 26 other reservoirs in the state.
In 2012, a record number of eggs — 13.1 million — were taken from Blue Mesa kokanee. Statewide, only an additional 3.2 million were taken at other waters. Hatchery workers handled about 20,000 fish to reach that level of egg production.
Parks and Wildlife has taken extra precautions the last two years to ensure an adequate number of eggs is collected. Just like last year, agency staff secured a fence across the East River near the Roaring Judy Hatchery where the fish are spawned. The fence prevented kokanee from traveling past the canal that leads into the hatchery, so more fish gathered in the spawning area.
"That's definitely helped to increase the egg take," said Dan Brauch, aquatic biologist in Gunnison.
Biologists also work to protect the fish in the spring when young kokanee, about 2 inches in size, are released from the hatchery for the 20-mile swim to Blue Mesa Reservoir. On the day the fish are released, biologists work cooperatively with local landowners to close or screen irrigation ditches along the East and Gunnison rivers for a few hours to prevent the tiny fish from leaving the main channel, thus assuring that more young fish make it to the reservoir.
Parks and Wildlife has also bolstered the population of kokanee in the reservoir by releasing more fish in the spring. During each of the last four years, the agency has increased the number of fingerlings released into the reservoir by about 500,000, bringing the total number stocked annually to about 3.5 million.
Protecting kokanee also extends to the fall when the most lake trout are removed. This year biologists only removed lake trout that were 32 inches or less in length. In previous years fish 38 inches or less were targeted. The change was made because lake trout in the smaller category comprise the largest population segment and therefore consume the most kokanee.
During the last four years, biologists have removed about 4,700 lake trout from the reservoir, including just more than 800 this year. In the last three years, anglers have harvested about 17,000 of the species.
"We'll continue to remove lake trout from Blue Mesa and we encourage anglers to keep the fish they catch, especially those that are less than 32 inches," Brauch said. "We'll be evaluating our data during the next six months to determine next year's removal plan."
In a new development this year, 70 of the captured lake trout were transplanted to Twin Lakes near Leadville. To help boost overall angling opportunity in Colorado, biologists hope to move more lake trout to other waters next year.
"A variety of management actions is needed to improve the situation at Blue Mesa," Alves said. "We'll continue lake trout removal. Research and surveys are ongoing. And we'll work to maintain a strong kokanee egg harvest and our significant stocking effort," Alves said.blog comments powered by Disqus