Kokanee take a dive in Lake Granby — The Sky-Hi Daily News

From the Sky-Hi Daily News (Hank Shell):

The numbers are in, and once again, the cards seemed to be stacked against the kokanee salmon population in Lake Granby.

This year’s annual kokanee salmon egg collection at Lake Granby yielded around 72,000 eggs, an alarming drop from the 357,000 eggs collected in 2013.

“This is the worst egg take since 1999,” said Jon Ewert, a biologist with Colorado Parks and Wildlife.

Ewert heads the annual egg count in Grand County, which includes Granby, Wolford and Williams Fork reservoirs.

“Historically, Granby used to be the biggest producer of eggs for the whole state, and it used to be the only source of eggs that we needed,” Ewert said…

Perfect storm

The question of why the kokanee are struggling in Lake Granby is a complicated one, and some are quick to point to one culprit – lake trout.

Lake trout, which eat kokanee, have grown in numbers in recent years, putting pressure on the kokanee population. But Ewert said the equation is more complicated.

Recent high water years have favored Mysis shrimp, which compete with the kokanee for zooplankton.

Lake Granby has a tendency to stratify in normal to low water years, which means warm water rises above cold to create two separate zones.

Mysis shrimp are usually confined to cold bottom layer, while kokanee and zooplankton stay in the warmer top layer, Ewert said.

In high water years, the lake takes longer to stratify, giving the shrimp access to the zooplankton for longer.

The high variability of water levels makes it difficult to maintain a consistent fishery.

“You’re always trying to achieve a balance between the Mysis, lake trout, kokanee and zooplankton,” Ewert said. “Those are kind of the main players, but the scale is always tipping one way or the other. There are very few years when you can say that it’s perfect.”

If the interplay of environmental pressures isn’t enough, Ewert said spilling over Granby Dam has also had an impact on the kokanee population.

Specifically, Ewert pointed to 2011, which was a heavy spill year. That year, CPW found kokanee at the bottom of Granby Dam.

This would be about the time when population impacts from spilling in 2011 would become apparent, Ewert said.

“There’s definitely a relationship there, too,” Ewert said.

Searching for solutions

CPW has been looking for a solution to Lake Granby’s kokanee problem in recent years.

But restocking isn’t enough to prop up Laky Granby’s dwindling population, and the CPW has been asking anglers in Lake Granby to keep their limit of Lake Trout.

Additionally, Ewert said that an increase on the bag limit for lake trout is a possibility.

But Keefe, whose main livelihood is trophy lake trout, said any future action needs to take the economic benefits of the lake trout fishery into account.

“If we’re changing the limits, we’ve got to make sure we’re changing them where it’s good for the long haul,” Keefe said. “If we take big fish out of the lake then we may never see them again.”

A healthy lake trout populations does rely on a healthy kokanee population, Ewert said.

Keefe suggested a slot limit, to help protect the trophy mackinaw that draw so many to Lake Granby.

Currently, Keefe said he asks anglers to throw back lake trout over 20 inches.

“Very few fish make it past 20 inches,” Keefe said.

An increase in the bag limit isn’t necessarily on tap for this year, but anglers could see one in the future, Ewert said.

“A lot of it is going to depend on what kind of a snow year that we have,” he said.

More Colorado-Big Thompson Project coverage here.

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