Colorado Parks and Wildlife proposes new fishing regulations for state’s largest, densest lake trout fishery

On the evening of March 15, Jon Ewert, a fisheries biologist with Colorado Parks and Wildlife, spoke at a community meeting about the Lake Granby fishery and presented proposed rule changes. The aim of the proposal is to improve the quality of fishing for trophy lake trout.

The proposal would increase the bag and possession limit for lake trout from four to 12, but only one individual larger than 24 inches in length can be caught per day. There are currently no length restrictions. Additionally, the catch and possession limit for trout – except lake trout – and kokanee will be changed to four year-round. The hooking season, during which fish are hooked outdoors, will be removed.

Ewert explained why he proposed these rule changes by discussing the fish research he has been conducting in Grand County since 2011. Every year, Parks and Wildlife casts gillnets at different depths, in the same places and on the same dates. Then, a different type of netting study is carried out – the studies are independent of each other. This gives Ewert enough data to make reasonable and accurate estimates representing fish populations, including the size of each species.

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Data shows that Lake Granby has the largest and densest population of lake trout in Colorado – approximately 159,000. However, there are two populations of lake trout – fish under 24 inches and fish over 24 inches. The difference is that lake trout over 24 inches are completely dependent on larger vertebrate prey.

“Our population estimates turned out to be very far off and completely dwarfed any lake trout catch in the state,” Ewert said.

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About 93% of lake trout caught in the Granby study were less than 24 inches. Relative weight measures the health of the fish, which means that a certain length should be equal to a certain weight or a relative weight of 100.

“It’s not only a measure of the condition of individual fish, but also a measure of the number of predatory fish relative to available prey,” he said. “If you have a lot of lake trout living off smaller stocks, they will be thinner.”

Data from Lake Granby consistently show that lake trout over 24 inches in length have poor body condition, with an average relative weight of 79.5 compared to fish under 24 inches in length.

Ewert explained that Lake Granby has the state’s largest population of Mysis shrimp, which feed on zooplankton – the same food that salmon depend on. Shrimp is an excellent food for small lake trout, but not for large trout.

“This is a classic case of unintended consequences,” Ewert said. “Instead of introducing a truly valuable prey source into the Kokanee in the form of Mysis shrimp, they became competition.”

In other reservoirs, such as Williams Fork and Green Mountain, where Mysis shrimp are less abundant, lake trout populations have higher relative masses.

Kokanee salmon are the most valuable game available in Lake Granby and can produce trophy lake trout. Dietary studies show that lake trout larger than 35 inches are almost entirely dependent on rainbow trout and salmon.

Ewert believes Lake Granby needs the Kokanee population to recover and sustain itself, which has not happened since 2011. Granby salmon are supplemented by other egg sources. Additionally, when Kokanee fights lake trout, it feeds on catchable, stocked rainbow trout.

Parks and Wildlife supports trophy fishing in Granby by stocking rainbow trout due to the small kokanee population, which is not the intended goal. According to Ewert, approximately 94,000 rainbows will be stored in Lake Granby in 2024 at a cost of approximately $90,300.

“Recreational fishing in Grand County generates approximately $30 million in economic benefits each year,” Ewert said. “The only recreational activity that generates greater economic impact in Grand County is skiing.”

Anglers are interested in Lake Granby for its trophy fishing, but stocking and reliance on hatcheries are limited. Ewert wants the fishery to become more self-sustaining, trying to rebuild the kokanee population that feeds the lake’s trophy fish while also increasing fishing opportunities for those who want to catch salmon.

The newly proposed regulations for Lake Granby better reflect current conditions and are more “customer friendly,” Ewert told meeting participants. They are also more consistent with other trophy fisheries.

One of the men announced, “That’s an awful lot of fish!” regarding increasing bag limits for lake trout.

Ewert told participants he believed the proposed changes may not make a measurable difference to the lake trout population and could improve lake trout body condition.

“This is a step we must take if we have any hope of rebuilding the Kokanee population,” he said. “And improving the condition of these lake trophies.”

The proposal will be submitted to Parks and Wildlife this June and will go through a review process, then agency commissioners will decide in November whether to approve it. If approved, the new regulations will come into force in April 2025.

Tara Alatorre is the editor of Sky-Hi News. She can be reached at 970-557-6031 or [email protected].