Hatchery-raised trout are a very important part of Idaho’s fisheries management. They often provide immediate fishing opportunities when stocked in Idaho lakes, reservoirs, ponds and streams, especially when natural populations or habitat cannot meet fishing demand. Idaho’s trout stocking program includes 10 hatcheries and raises more than 17 million fish annually, of which about 1.5 million are “catchable” size rainbow trout.

Because raising and stocking brood trout is expensive, fish and game biologists have put a lot of effort into improving the stocking program. In recent years, biologists have tried to answer the question: Is bigger always better? This group of studies investigated whether stocking larger trout might benefit anglers and whether it was cost-effective.

The results were surprising and earned Idaho recognition from the American Fisheries Society, which awarded Idaho Fish and Game biologists with its 2023 Distinguished Project Award for Fisheries Research and Surveys.

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According to Bo Guenther, state fish production director, “Idaho has a long history of using research to improve our trout stocking program. The Trout Magnum Program is a great example of how we can incorporate research into our stocking program to make fishing better while making our operations more efficient.” .

Fish and game biologists and hatchery managers faced an immediate challenge trying to determine the best size of trout to stock for anglers. Every trout hatchery in Idaho raises fish at full capacity, so the space required to raise larger trout will mean fewer fish available for stocking.

Common sense would say that declining trout stocks mean fewer fish being caught by anglers, but fisheries managers have had a hunch that may not be correct. One way to find out is to apply fisheries research techniques and cost/benefit analysis to see if stocking fewer trout — but larger quantities — will provide better fishing.

Biologists know from previous research that larger trout are caught at a higher rate than smaller ones, so does less mean more? As in, could a smaller number of larger trout be stocked, but a higher percentage end up as fish? If so, what is the difference in cost?

Their research required careful planning years in advance to raise and tag tens of thousands of rainbow trout before stocking them and then checking with fishermen to see how many fish were caught. The study included several hatcheries and dozens of waters across the state, and most of the data came from tagged trout that anglers reported catching.

Biologists compared anglers’ catch rates for two sizes of rainbow trout: the standard size (10 inches) known as “catchables” and the “magnum” trout (12 inches). These fish have been stocked in many different sized waters throughout Idaho. Feed costs were also compared between the two since it takes more food and more time in the hatchery to raise a 12-inch trout than a 10-inch trout.

Fish and Game’s goal is for anglers to catch and stock the trout it raises. Although “magnum” trout cost 31% more in feed than smaller trout, anglers catch 100% more of the larger trout than the smaller ones.

The research also found that, if desired, hatchery managers could offset the increase in food costs by raising smaller but larger quantities of trout, and anglers would benefit by catching more and larger fish, despite the reduced number of stocked trout.

Larger trout have also proven to be more cost effective when catch rates are taken into account. Despite the high cost of raising a 12-inch trout, it actually costs $0.54 less on average per trout an angler catches than it does per 10-inch trout caught because so many trout The big one ends up in the fisherman’s krill.

The result of the study changes the way fish and game fish raise trout. The Nampa Fish Hatchery has already converted its entire trout production to “magnum” and other facilities are moving in that direction as well. By questioning “common sense” logic and conducting research, Fish and Game’s findings have made hunting better for Idaho hunters. Furthermore, other states are putting the study results into practice as well, with several others already modifying their trout breeding programs further.

The American Fisheries Society recognized Idaho Fish and Game for “improving management of key sport fish species, increasing the survival of stocked sport fish, ensuring anglers have access to fishing areas, and continuing to encourage angling for the current and next generation of anglers.”

Michelle Matthews is managing editor of The Times News. Contact Matthews at mmatthews@magicvalley.com or 208-735-3233.

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