Ice fishers plumbing the waters of Granby Reservoir in search of lake trout this winter will likely experience a drop in daily catch rates compared to recent winters, and that, according to Colorado Division of Wildlife (DOW) aquatic researchers, is good news. A drop in catch rates on smaller lake trout is an indication that the researcher’s efforts to revitalize the venerable yet slumping fishery are paying off.
During the years of drought that straddled the turn of the century, Granby’s lake trout and kokanee populations fell out of alignment. Lake trout, known as mackinaw or macks, had overpopulated and toppled the balance of the reservoir’s ecosystem. There were far too many of the predatory macks and not enough kokanee. Kokanee numbers were down because of shrinking water levels, over predation, and reduced kokanee egg supplies. Without the kokanee, their primary source of forage, the macks went hungry.
Starving fish make easy targets, and the near phenomenal catch rates reported by ice anglers prior to 2005 verified the macks’ grim predicament. As a result, growth rates stood virtually at a standstill.
Granby Reservoir lake trout now are showing improved body condition and growth rates.“We were able to look at tagged fish (lake trout), there were individuals that did not grow even one inch in ten years,” DOW aquatic biologist Pat Martinez said, “they were totally stunted, and with that many mouths looking for something to eat just to stay alive, kokanee didn’t have a chance.”
“It is a much more positive story now, with positive responses in the fishery for everybody. Larger lake trout are still there, they are thriving and their body condition and growth rates are improving, and those improvements are going to translate into some truly awesome, highly-appealing lake trout down the road.”
The kokanee fishery also has rebounded. Stocking numbers are up, and the traditional kokanee egg take has resumed. The benefits of a healthy kokanee population spill directly over into the mackinaw side of the equation. Research shows a significant improvement in relative weight on lake trout because kokanee are back in the picture, the reservoir level is up, and there is cooler water above where the macks can come up for the forage.
Bill Atkinson, DOW aquatic biologist at Granby Reservoir said, “In 2003, I started stocking a million kokanee a year and then I got 35,000 additional catchable rainbows. With this increase in forage, I expected the lake trout catch to drop and, in fact, if it didn’t I would be very concerned.”
Granby Reservoir ice angler using sonar and a two-rod system to catch lake trout. It’s a new era for mackinaw in Granby Reservoir these days; there is more water, more to eat, and a lot more structure. While macks in summer favor the dark quiet waters below the thermocline, hanging around rocky structures rising from the mysterious depths of the reservoir, macks in winter also like to be near structure but they move higher in the water column. It is common to find them in depths ranging from 15 to 50 feet.
With reservoir levels in Granby near capacity, anglers today are finding macks revisiting their favorite haunts of the late 80’s and early 90’s. Known locations include the channels around Harvey Island, Shelter Island, the rocky ridges and humps off Dyke #3, Inspiration Ridge in Arapahoe Bay, the slopes around Deer Island, Rocky Point in Columbine Bay, and the Pump House Flats.
With the macks now spread out over a larger area and better fed, anglers might consider employing some of the techniques that proved successful under similar conditions in the past. One technique involves using a sonar unit, a pair of holes augured in close proximity, two rods, and two entirely different jigging motions. The technique is designed to “attract and trigger”.
An ice angler tussles with a Granby Reservoir lake trout. The profile of Abe Lincoln lying down is visible on the peaks in the distance.Lake trout are curious fish, easily attracted to the flashes and the erratic motions of a shiny metallic jigging spoon. While a starving mack might rush in and attack without hesitation, this is not the case with a well-fed predator. Monitoring the action below on a sonar screen, ice fishers often will see macks appear on the scene but refuse to hit the spoon. The macks seem content to hang in the shadows and watch the entertainment.
However, waiting nearby at the bottom of the second hole is the closing act, a soft and squirmy plastic tube jig sweetened with a slender strip of white sucker filet. Its purpose is to appear at just the right moment to trigger the macks instinct to strike. While the macks are enjoying the dancing spoon, it falls abruptly to the bottom and lies still. Almost simultaneously, the tube jig rises from the bottom and begins its slow seductive dance. Show over.
Credit: Outdoors Journal is a monthly feature of the News and Media section of the Colorado Division of Wildlife. The Journal provides timely articles and photo-essays on hunting, fishing, and other outdoors activities, including in-depth reports on interesting scientific projects and the people behind the scene.
Additional information available by contacting Dennis McKinney at Dennis.McKinney@state.co.us or 303-291-7371.
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