IDFG’s new approach to stocking rainbows

What a difference a year makes. A new stocking program keeps rainbow in the hatchery for an extra year resulting in a fish that is about 70 percent bigger than the standard stocked catchable trout. IDFG photo.

Columbia Basin Bulletin/IDFG

BOISE, Idaho — Raising rainbow trout to a larger size in hatcheries has proven to be both financially beneficial for the state of Idaho and a plus for anglers, according to a four-year study completed by the Idaho Department of Fish and Game.

The results of the study using an evaluation tool developed by IDFG fishery biologists has Fish and Game managers taking a new approach to stocking larger rainbow trout in many of Idaho’s lakes and reservoirs.

This year, many of the state’s most heavily stocked still-water fisheries will be stocked with large numbers of 12-inch rainbow trout, called magnums by Fish and Game biologists, instead of the 10-inch trout that have long been the agency’s standard. While anglers will likely view this as an opportunity to catch larger fish, it is also an opportunity for Fish and Game to provide angler-friendly catch rates on a tighter budget.

The most striking results in the statewide study came from Idaho’s larger lakes and reservoirs that are most dependent on hatchery stocking to provide the bulk of the trout fishing.

Angler Kevin Hamilton of Boise caught this wild rainbow on the Boise River in February. Kevin Hamilton photo.
Angler Aubri Blaser of Boise, caught this wild rainbow in the Payette River just below Banks, Idaho in February. Kevin Hamilton photo.

The study showed that 12-inch rainbow trout were caught by anglers at a higher rate than 10-inch fish. The study showed that less than 1 of the standard 10-inch rainbows was caught for every three stocked, but anglers caught more than one 12-inch trout for every two that were stocked.

A 12-inch rainbow trout weighs about 70 percent more than a 10-inch trout. It takes more feed to grow them bigger, so each one costs more to produce.

“We don’t have more money to buy more fish food, so the shift to larger trout will mean that fewer trout can be produced and stocked,” said Gary Byrne, IDFG Fish Production manager.

“The study shows that in places where we switch to stocking larger trout, less means more,” said Jeff Dillon, the state agency’s fishery manager.

“The waters that will be stocked with 12-inch trout will receive stocking numbers reduced by about 40 percent but since larger trout are caught at almost twice the rate, the number of trout that anglers catch will actually be higher and anglers will enjoy the added bonus that the trout they catch will be 2 inches larger.”

Why is it working?

Researchers theorize that the ability to survive until anglers come calling is a factor.

It is likely that the 12-inch fish are too big for cormorants and pelicans or simply better at escaping predators than the smaller rainbows.

The larger fish may also be better equipped to make the transition from hatchery holding-feeding ponds to the wild.

“It’s probably a combination of things,” Dillon said.

Catchable fish are stocked in the Spring, Summer and early Fall at many ponds and lakes throughout the state. IDFG photo.
Catchable fish are stocked in the Spring, Summer and early Fall at many ponds and lakes throughout the state. IDFG photo.

“Our four-year evaluation is the most robust and conclusive evaluation of our trout stocking program ever done in the history of IDFG,” said Fisheries Chief Ed Schriever.

“The results clearly show that in many Idaho waters anglers catch stocked 12-inch rainbow trout at a higher rate than 10 inch trout,” according to Schriever. “Without the cooperation of Idaho anglers, this study would not have been possible.”

“We thank all of those who participated for helping us improve the effectiveness of our trout stocking program. I think anglers will enjoy the changes we are making to the stocking program as a result of the evaluation.”

The new strategy is almost certain to be good for many businesses as well, since every dollar spent stocking trout in Idaho returns approximately $35 to the state’s economy.

Dillon said that the IDFG’s resident fish hatchery program, which feeds about 900 water bodies, prompts about $120 million annually in spending in local economies, according to a survey conducted in 2011.

The shift towards fewer, larger hatchery fish will continue over the next 18 months. By the summer of 2016, about half of the 800,000 pounds of catchable-size rainbow trout stocked in Idaho will be 12-inch fish. Most of the bigger fish will be released into the bigger systems, such as Lake Cascade, American Falls and Blackfoot reservoirs.

Producing and stocking rainbow trout for anglers is the single most expensive license funded fishery program managed by IDFG. The majority of funding to operate the trout stocking program comes from the sale of fishing licenses.

Here is the latest IDFG magnum stocking locations:

Deyo Reservoir

Bull Trout Lake

Lucky Peak Reservoir

Mann Creek Reservoir

Sage Hen Reservoir

Cascade Lake

Horsethief Reservoir

Lost Valley Reservoir

Upper Payette Lake

Warm Lake

Little Wood Reservoir

Oakley Reservoir

Blackfoot Reservoir

Chesterfield Reservoir

Deep Creek Reservoir

Foster Reservoir

Glendale Reservoir

Lamont Reservoir

Twin Lakes Reservoir

Island Park Reservoir

Mackay Reservoir

Ririe Reservoir

Stanley Lake