Rainbow and brown trout numbers are down in the upper portion of the world-renowned Bighorn River trout fishery this fall, based on recent Montana Department of Fish, Wildlife and Parks sampling.
The target for the upper three miles of the river below Yellowtail Dam is 5,000 fish over 6 inches per mile. This fall, the estimate put trout numbers at about 3,000 per mile — 2,200 brown trout and 860 rainbow trout, said Mike Ruggles, FWP fisheries biologist.
“Overall, it’s better than when we were in a drought,” he said in a presentation to the Bureau of Reclamation, other agency officials, anglers and conservationists at a meeting Thursday.
Part of the reason for the drop is that older brown trout are dying and there’s not a strong juvenile class of fish to replace them, partly because of low river water flows, he said.
On what’s termed the lower section of the upper river, FWP counted 1,300 brown trout and 400 rainbow trout over 6 inches per mile. Size distribution-wise, Ruggles said things look pretty good, but there are fewer juvenile brown trout in the system. That will make room for more rainbow trout, although the fish will be smaller.
“The good news is that in the low water years we are seeing some recruitment of rainbow trout,” he said.
On the Bighorn Reservoir which feeds the trophy trout stream, Ruggles said he is surprised there aren’t more anglers considering the health of the fishery.
“I can’t believe people aren’t climbing over each other to fish down there,” Ruggles said. “It’s a tremendous fishery.”
The portion of the reservoir in Montana is managed by FWP, while Wyoming Game and Fish Department manages the southern half of the water body.
Ruggles said FWP will continue to stock sterile walleye into the reservoir to ensure that there is a trophy walleye fishery to attract anglers. The walleye are sterile to ensure they don’t interbreed with native sauger, which are being protected because they have been deemed a unique species.
While the sauger are healthy in the reservoir, they won’t grow to 30 inches like the walleye do. A large sauger is a 20- to 25-inch fish. More common are 15- to 20-inch sauger.
Smallmouth bass, brown trout and ling round out some of the more popular game fish in the reservoir. Ruggles noted that this fall his fisheries crew netted one 8-pound ling that had a 4-pound carpsucker in its mouth.
On the Wyoming end of the reservoir, Sam Hochhalter of WGFD, said there is an “amazing diversity of gamefish” with anglers mostly targeting catfish, walleye and sauger.
Emerald shiners, a baitfish, are key to keeping all of the predacious fish well fed. And those baitfish seem to thrive when the reservoir’s elevation is at 3,640 — which is where it was sitting on Nov. 1.
Wyoming has not stocked walleye on its end of the reservoir since 2000. Since then, the agency has seen declining catch rates of the fish while sauger catch rates have climbed. Those sauger numbers may diminish, though, Hochhalter said, as a strong 2004 age class dies off.
“We’re riding a pretty good wave of catfish and sauger” recruitment and catch, Hochhalter said. “It was a great ice-fishing season last year.”
To keep the Bighorn Reservoir’s sauger numbers strong, WGFD and FWP have been working for the past three years to capture spawning sauger in the upper river, milk them for eggs and sperm, and rear the young in the Miles City hatchery. So far, the work has suffered from several challenges.
While the agencies had hoped to stock 250,000 to 500,000 sauger annually from the work, in 2011 only 48,000 were stocked, in 2012 none were stocked and in 2013 105,000 were stocked.
“We’re still figuring things out,” Hochhalter said.
This spring, the agencies tested using hormones to increase the chances that females would produce eggs, and also placed some of the fish in portable tanks to better control the water temperature and in an attempt to place less stress on the fish.
The study showed an increase of 11 percent between the control group and the fish that were treated and tanked, but the hormone-treated fish also suffered a higher mortality rate.
“So we are seeing some improvement,” Hochhalter said.