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On the evening of March 15, Jon Ewert, a Colorado Parks and Wildlife fisheries biologist, spoke at a community meeting about Lake Granby’s fishery and introduced proposed regulation changes. The proposal is intended to enhance the quality of the trophy lake trout fishery.
The proposal would increase the bag and possession limit for lake trout from four to 12, but only one greater than 24 inches can be taken per day. Currently there are no length limits. Also, the bag and possession limit for trouts — except lake trout — and Kokanee would change to four year-round. Snagging season, where fish are hooked externally, would be removed.
Ewert explained why he proposed these regulation changes by going over fish surveys he has been conducting in Grand County since 2011. Every year Parks and Wildlife sets gill nets at different depths in the same locations and dates. Then another type of netting survey is conducted – surveys are independent of each other. This gives Ewert enough data to make a reasonable, accurate estimates that represent fish populations, including sizes of each species.
Data shows that Lake Granby has the largest and densest lake trout population in Colorado with about 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 entirely dependent on larger vertebrate prey.
“Our population estimate came out to be far and away, completely eclipsing any lake trout fishery in the state,” Ewert said.
Approximately 93% of lake trout captured in Granby surveys were below 24 inches. Relative weight measures the health of a fish, which means a certain length should equal a certain weight, or a relative weight of 100.
“It is not only a measure of what condition that individual fish is in, it is also a measure of how many predatory fish there are relative to the prey they have available,” he said. “If you have a lot of lake trout living off of fewer resources they are going to be thinner.”
Lake Granby’s data consistently shows that lake trout over 24 inches have a poor body conditions with an average relative weight of 79.5, compared to fish less than 24 inches.
Ewert explained that Lake Granby has the highest population of Mysis shrimp in the state, which eat zooplankton – the same food salmon depend on. The shrimp are a great food for small lake trout but not for large trout.
Aquatic biologist Jon Ewert holds a male Kokanee salmon during spawning operations at Wolford Reservoir in October, 2022. Colorado Parks and Wildlife/Courtesy photo
“This is a classic case of unintended consequences,” Ewert said. “Instead of introducing a prey source to Kokanee that was really valuable in the form of Mysis shrimp, they became a competitor.”
Other reservoirs like Williams Fork and Green Mountain, which have less Mysis shrimp, have lake trout populations with higher relative weights.
Kokanee salmon are the most valuable prey available in Lake Granby for producing trophy lake trout. Diet studies show that lake trout bigger than 35 inches are almost entirely dependent on rainbow trout and salmon.
Ewert believes Lake Granby needs the Kokanee population to recover and support itself, which has not happened since 2011. Other egg sources are supplementing Granby’s salmon. Plus, when Kokanee struggle lake trout prey on catchable, stocked rainbow trout.
Parks and Wildlife is supporting the trophy fishery in Granby by stocking rainbow trout due to the low population of Kokanee, which is not the intended purpose. In 2024, approximately 94,000 rainbows will be stocked in Lake Granby for a cost of about $90,300, according to Ewert.
“Recreational fishing in Grand County supports about $30 million of economic benefit every year,” Ewert said. “The only recreational activity that generates more economic impact in Grand County is skiing.”
Anglers are interested in Lake Granby for its trophy fishing, but there is a limit to stocking and relying on hatcheries. Ewert wants the fishery to become more self-sustainable by trying to restore the Kokanee population that feeds the trophy lake trout, while increasing angler opportunities for those wanting to fish for salmon.
The newly proposed regulation on Lake Granby better reflects the current conditions and are more “customer friendly,” Ewert told the attendees at the meeting. They are also more in line with other trophy fisheries.
One man proclaimed, “That’s an awful lot of fish!” in regards to the increase bag limits for lake trout.
Ewert told attendees that he thinks the proposed changes may not cause a measurable difference in the lake trout population, and it may increase the lake trout body condition.
“It is a step that we need to take if we have any hope of recovering the Kokanee population,” he said. “And increasing body condition of those trophy lake trout.”
The proposal will be submitted to Parks and Wildlife this June and undergo a review process, then the agency’s commissioners will decide whether or not to approve them in November. If approved, the new regulations will go into effect in April 2025.
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