Colorado biologists tackle Lake Granby kokanee salmon decline

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Kokanee salmon caught at Green Mountain Reservoir, Summit County, Colorado. bberwyn photo.

Public meetings on Lake Granby fishery set for early spring

By Summit Voice

FRISCO — Colorado Parks and Wildlife biologists say they’re considering changes to fishing regulations in Lake Granby to try and recover the population of kokanee salmon in the popular lake.

The number of salmon eggs collected by biologists in Lake Granby has dropped from 4 million in 2006 down to just 350,000 this year, not enough to maintain the existing population, let alone stock any other Colorado lakes with kokanee.

Kokanee are land-locked Pacific sockeye salmon found in several high-elevation reservoirs in Colorado. The fish feed primarily on zooplankton. But a booming population of mysis shrimp and predation by lake trout are probably the main factors in the Lake Granby kokanee decline.

“Lake Granby kokanee need to produce 1.2 million eggs just to sustain their population there,” said biologist Jon Ewert. “We are well below that number so we won’t be stocking other waters with eggs from here until we can get this situation turned around.”

Mysis populations rise during high-water years and fall during periods of low-water levels, Ewert explained. According to this scenario, the substantial rainfall and snowpack this year may contribute to higher numbers of mysis in the next several years, a situation that will weigh on future management decisions regarding how the issue is eventually addressed.

Ewert said that biologists cannot influence mysis densities in the reservoir, but they can find a viable solution for the predation side of the equation.

“Based on the data and information gathered, we believe that the lake trout can definitely sustain a higher level of harvest in Lake Granby,” Ewert said. “We increased the lake trout take limit in 2006 but have continued to see their numbers increase while kokanee numbers decrease, so the goal is to manage more effectively.”

Ewert adds that fewer kokanee has led to poor body condition in large lake trout.

“Many of the lake trout I have seen are very skinny, essentially starving because their primary food source has become scarce,” he said. “This is a clear sign that we need to do more to address the current predator and prey imbalance in the reservoir.”

In March of 2014, Colorado Parks and Wildlife officials plan to invite the public to several meetings where they can review biological data and discuss the direction of fishery management in Lake Granby with state wildlife officials.

For more information, visit www.wildlife.state.co.us/Research/Aquatic/ColdwaterResEcology/Pages/ColdwaterReservoirEcology.aspx.

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One Response

  1. Maybe they shouldn’t be there in the first place…

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