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Wyoming Game and fish Department fisheries biologist Bill Wengert, a 35-year veteran, found out just how tricky it can be to age a fish recently when he caught a lake trout on Flaming Gorge Reservoir.
"I was ice fishing in the Big Bend area when I caught a lake trout weighing a very skinny two and a half pounds and measuring 22.75 inches in length,"; Wengert said. ";The fish showed no signs of any obvious hook scars, not saying it had never been caught previously, but a lot of lake trout in the Gorge are hooked-scarred. I thought that was unusual.
"As I looked closer I noticed the adipose and right pelvic fin of the lake trout had been clipped, so I knew the fish was stocked. Looking back in time to Game and Fish historical stocking records for Flaming Gorge Reservoir I determined the fish was stocked on April 14, 1983, at an average length of 8.3 inches. The fish were loaded onto a barge and transported to the middle of the reservoir off of Buckboard Bay. Only 11,656 lake trout were stocked on that day. This means the fish spent nearly 25 years in Flaming Gorge Reservoir and was 26 years old, including one year in the hatchery."
Fisheries biologists use scales, fin rays, bones and otoliths ('oto' means ear and 'lith' means bones) to determine the age of fish because these fish parts often form yearly rings (annuli), just like a tree. Otoliths help the fish keep its balance in the water. When an otolith is removed from a fish, sectioned into thin slices and viewed through a microscope, it reveals a series of growth rings. Otoliths are more commonly used to age fish because they provide the most accurate ages, particularly in older fish.
"I have looked at thousands of fish in my career and I never would have guessed that fish was so old,"; Wengert said. ";What is really amazing about this whole event is that, from my perspective, I may have actually clipped the fins on this very fish and I know I was driving the barge when the fish were stocked, nearly 25 years ago."
Wengert says long-lived fish, such as lake trout, are like humans in that they vary in size no matter how much food is available to them.
"A fish's genes also determine how large they will grow. Some fish are programmed, if you will, to be large and others, small,"; he said. ";That applies to fish from wild populations to those reared in a fish hatchery. There was plenty of food for this one lake trout to eat when it was stocked 25 years ago and it only grew to be two and a half pounds."
Data on the length-frequency of lake trout from gill nets set in Flaming Gorge Reservoir from May 1990-2004, revealed that, in 2004, one fin-clipped lake trout measuring 35.6 inches and weighing 17.1 pounds was captured in the Big Bend area. This fish was stocked the same time as the much-thinner fish Wengert caught through the ice.
"When you think of the record lake trout taken out of the Wyoming portion of Flaming Gorge Reservoir, 51 pounds, this fish paled in comparison in size, but its capture allowed fish managers an opportunity to learn more about fish genetics, age and growth of lake trout in the reservoir," he said. "The adage is true: You can learn something new every day."
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