Biologists strive to balance fish populations in a reservoir critical for Kokanee salmon; record egg harvest will help sustain Kokanee spawning program
By Summit Voice
SUMMIT COUNTY — Colorado Parks and Wildlife collected 11 million eggs from kokanee salmon running out of Blue Mesa Reservoir this fall. The record harvest will ensure that Colorado Parks and Wildlife will have adequate supplies for stocking 26 reservoirs around the state with salmon fry next year.
But biologists say much more work needs to be done before they declare the population of kokanee salmon in the 9,000-acre reservoir recovered. Kokanee numbers have declined precipitously during the past 10 years as the population of predatory lake trout boomed, knocking the fishery out of balance.
“One good spawning run does not mean we’ve fixed the problems,” said John Alves, senior aquatic biologist for Colorado Parks and Wildlife’s southwest region. “Blue Mesa is critical for our statewide kokanee program and the fishery is out of balance. There is no quick fix.”
Biologists estimate the reservoir’s kokanee population at 280,000, down from about than 1 million a decade ago.
Blue Mesa Reservoir is a man-made body of water, so managing fish populations that did not evolve together poses significant challenges. While Blue Mesa’s trophy lake trout often capture headlines, surveys show that more than 80 percent of the reservoir’s anglers fish for kokanee, rainbow trout and brown trout. The kokanee population is intensively managed. Every year during fall, kokanee swim 20 miles up the Gunnison and East rivers to the Roaring Judy hatchery where they are spawned.
As the state’s largest kokanee fishery, Blue Mesa produces more eggs than any other reservoir and on average accounts for 60 percent of the overall egg take in the state. This year just over 2 million eggs were harvested from the state’s other kokanee fisheries, underscoring Blue Mesa’s importance for Colorado’s kokanee anglers.
Alves explained that egg collection is highly variable from year-to-year and from one body of water to another.
“There are a multitude of factors that account for egg take; the high number does not mean we have a record number of kokanee,” Alves said.
Several factors may have contributed to the record egg production this year. Hatchery staff improved management techniques to assure that more fish make it into the hatchery where spawn is taken. These included: placing a net across the river near the outlet channel at the hatchery to keep fish from swimming past the hatchery; and preventing kokanee from moving out of the spawn-take facility once they’ve entered the channel.
In addition, egg production from individual female salmon set a record this year. A total of 7,537 females were spawned and each produced an average of 1,464 eggs.
Two years ago Colorado Parks and Wildlife designed a new fisheries management plan for Blue Mesa which includes removal of lake trout. This year 1,333 lake trout were removed, with 1,298 of those–97 percent–under 30 inches in length. A total of 35 fish that measured from 30 to 38 inches were removed. Five fish that measured more than 38 inches were released back to the reservoir.
Based on their long-term knowledge of the reservoir, biologists zeroed-in on locations where the population of smaller lake trout is greatest.
“We target the fish that are 30 inches and under because overall they consume the biggest number of kokanee,” Alves said. “But we know from our surveys that lake trout over 30 inches are significant predators, consuming more than 25 pounds of fish, mainly kokanee and rainbow trout per year. Therefore it is important that we remove some of these fish in our effort to balance the fishery.”
To help fortify Blue Mesa’s overall kokanee population, biologists increased the number of kokanee fry released into the reservoir by about 500,000 for each of the past three years. About 3.4 million fingerlings are released annually, with 3.1 million released into the East River, and another 300,000 stocked by truck directly into the reservoir. Biologists have taken steps to make sure that the fingerlings released into the river make it to the reservoir. Screens are placed across irrigation ditches to prevent the small fish from entering those channels where they can’t survive.
Maintaining an outstanding kokanee fishery is the top management objective at the reservoir for Colorado Parks and Wildlife. Anglers reported landing about 44,000 kokanee in 2011, more than double 2010′s take but significantly less than the 130,000 fish harvested in 2002.
“We’re seeing some signs that the kokanee are increasing, but we’re far from where we need to be to ensure that Blue Mesa will continue as a high-quality kokanee fishery,” Alves said.
Providing angler opportunity for trophy lake trout is also a management goal. Biologists’ fish surveys this year showed that the body condition of lake trout is continuing to improve. More of the fish are round and plump — as they should be — instead of long and thin. While lake trout are able to survive on little food, they don’t gain weight if they face too much competition for food.
“Lake trout anglers don’t want to catch skinny fish,” Alves said. “Without kokanee, trophy lake trout opportunities will decline. We must maintain a biological balance in the reservoir, increase the number of kokanee and provide opportunities for the greatest number of anglers.”
Angler harvest of lake trout is another key to restoring balance to the fishery. Colorado Parks and Wildlife has encouraged harvest of lake trout during the last few years and anglers appear to be taking up the challenge. This year anglers harvested a record 5,670 lake trout, up from 3,849 in 2010 and more than the previous record of 4,664 in 2007.
Still, restoring the balance at Blue Mesa will require a long-term, on-going effort, Alves said.
“We really appreciate that anglers are stepping up,” he said. “Angler harvest can really help us to maintain a balanced fishery.”