Culling overpopulated Blue Mesa fish helps feed local families

Program to continue in the spring

This is the season of sharing our bounty, and Blue Mesa Reservoir has an abundance of lake trout to spare. So as the holiday season set in this year, the Colorado Division of Wildlife went about giving the gift of fresh fish to dozens of area families, while trying to meet their own goals.

Blue Mesa is home to two species of salmonid, kokanee salmon and lake trout (mackinaw), that can grow to trophy size, some as big as 40 inches long and 50 lbs. Both species also bring in big money from anglers and coexist as predator and prey. In recent years that balance has been tipped in the mackinaw’s favor, with the trout growing larger and consuming more kokanee.
Kokanee won’t run upstream to spawn and die until they are three to five years old. Until then, they are fair game for the lake trout.
“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 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.
Brauch says average-sized lake trout are now eating more kokanee salmon than can be replaced through stocking. And if the DOW cannot sustain the kokanee population in Blue Mesa, there is little hope that populations can be sustained in the 25 other reservoirs in the state that rely on the “egg take” from Blue Mesa for stocking.
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 have seen a decreased population.
Things are out of balance in Blue Mesa Reservoir and the DOW is trying to restore order by removing a portion of the instigating mackinaw.
Brauch says lake trout 17 to 30 inches in length will eat 13 to 25 pounds of kokanee salmon a year and those are just the size of fish the DOW was targeting this year when they started a mackinaw-culling campaign to bring balance back to the system.
“We did wrap-up the work for this fall and I guess we were about able to remove the number we thought we would,” Brauch says of the effort. “In all, we captured over a thousand fish. Of those we tagged and released over 100 and culled about 900 fish.”
The culled fish were cleaned and filleted by volunteers and handed out to the public at three distributions at the DOW office in Gunnison.
DOW Area Wildlife Manager J Wenum says the practice of handing out fish and game isn’t uncommon for the DOW, which often finds itself with more meat than it can use.
“It’s not unusual for us to do this kind of thing when we have a fish salvage operation, like we would see during a drought or when repairs need to be made on a dam,” Wenum says. “We also hand out meat that has been taken illegally, through a donation process. We try to go through local social services or food banks or folk who would have a specific need for those types of things.”
 But since the Blue Mesa lake trout population is also being managed as a trophy fishery, not all trout were culled and handed out to the public.
“As we developed a plan for trying to reduce predation on kokanee, we recognize the value of lake trout,” Brauch says. “In the past we were just monitoring the population, so we marked and released all fish. But since we are trying to sort fish this year, we are doing the work in such a way that would maximize our ability to release big fish.”
Brauch said the division was able to accomplish that goal by dropping rubber gill nets eight feet tall and 25 feet wide in specific areas on the floor of Blue Mesa and let them soak for 45 minutes.
As a dozen people retrieved the nets over 19 days, they were able to mark fish larger than 30 inches and cull the others. Fish smaller than 17 inches could pass through the holes in the net unharmed.
Although some fish were marked this year, Brauch said, there still isn’t a good population estimate for lake trout in the reservoir, and the DOW is planning to continue the effort in the spring.
“It does take some amount of effort and it will likely take several seasons to see any benefits from the program,” he says. “But we aren’t anywhere near where we need to be in terms of the lake trout population.”
If the lake trout population goes unchecked, the DOW could face a shortage of kokanee salmon that could affect fisheries, and economies, across the state.
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. So the effect is far-reaching.”
But the kokanee population will not be bolstered by this year’s egg take, which was less than half of what has been taken on average since 1993. At the minimum, Brauch said the DOW needs about 3.5 million eggs to hatch at Roaring Judy Fish Hatchery and release back into Blue Mesa to maintain the population. This year they harvested only 2.4 million eggs.
“Statewide we had to look at many other places that we hadn’t looked at for eggs historically because of the shortages at Blue Mesa,” he said. “[Egg takes] aren’t anywhere near where they were. Fortunately, we were able to get eggs from some of these other waters this year. But that might not be the case in the future.”
Brauch hopes that if kokanee from Blue Mesa continue to produce relatively low numbers of eggs, the reservoir’s shared bounty of lake trout this year will be paid back as salmon eggs down the road.