Kokanee salmon caught at Green Mountain Reservoir, Summit County, Colorado. bberwyn photo.
New tool helps fisheries managers gather more eggs from other reservoirs
Staff Report
FRISCO — Colorado Parks and Wildlife biologists say they’ve wrapped up their annual kokanee salmon egg collection activities for the year, with good results at Wolford Mountain Reservoir, where they were able to gather 1.78 million eggs.
But predatory lake trout and other factors combined to suppress egg production in Lake Granby, historically the biggest source of eggs for the desirable sport fish.
Each year, crews collect the eggs during the fall spawning season. The eggs are hatched and raised at the Glenwood Springs fish hatchery, then stocked into the various reservoirs the following spring when they are one to two inches long.
The sharp drop in the number of eggs collected at Lake Granby raised some concerns.
“Wolford was the great overachiever, producing almost 18 times the number of eggs that we need to restock it,” said Hot Sulphur Springs-based CPS biologist Jon Ewert, who heads the egg collecting operations in Grand County. “As a result, we will use the excess eggs from Wolford to shore-up Lake Granby’s kokanee population.”
Ewert said Williams Fork produced enough eggs to sustain itself. Wolford’s success is due to the absence of predatory lake trout, competition from mysis shrimp and parasitic gill lice.
“Wolford is the only Middle Park reservoir with none of those three things, and we absolutely need to keep it that way,” Ewert said.
According to Ewert, the high water level in Lake Granby creates ideal conditions for a substantial increase in mysis shrimp numbers, which compete with kokanee for plankton, the fishes’ natural food. In addition, predation from a dense population of lake trout continues to negatively impact kokanee populations in the reservoir.
Little can be done to influence mysis shrimp populations, Ewert said anglers should keep the legal bag limits of lake trout to help maintain predator-prey populations in balance.
“We ask everyone to do what they can to help us recover our kokanee populations in Lake Granby,” Ewert said.
According to state biologists, Blue Mesa Reservoir in Gunnison County also experienced a decline in egg collection, adding that the decline in the top two egg producing reservoirs could have resulted in significant, long-term decline of the species if not for the use of an newly developed and highly effective fish trap.
“It’s called the ‘Merwin Net’ and we used it at Wolford and also at Lake Nighthorse, near Durango,” Ewert said. “This innovation allowed us to collect a large number of eggs and essentially prevented what could have been a crash in the state’s kokanee populations.”
According to CPW biologists, kokanee are a critically important species. They consume zooplankton, grow to a size that makes them a desirable sportfish and are considered excellent table fare. In addition, they provide a prey base to sustain lake trout, another desirable Colorado sportfish.
Because kokanee do not successfully reproduce at rates that are high enough to overcome the variety of pressures that affect their populations in Colorado, the manual collection of eggs is critical for their survival.
