One of Montana’s premier trout fishing streams, the Bighorn River, could be poised for an excellent season provided nothing “really weird” happens with spring runoff.
“People might not catch as many fish, but they will be a lot bigger on average,” said Mike Ruggles, fisheries manager for Fish, Wildlife & Parks’ Region 5 in Billings.
That could include the occasional brown trout weighing 6 to 8 pounds with a few over 10 pounds.
“The five-pounders are like footballs,” he said.
Those larger fish were flushed downstream from Bighorn Reservoir in one of the three big water years the river has experienced since 2011, which set the tone for some massive spring storms and runoff.
Dam managers, landowners, outfitters, guides and anglers are hopeful this spring may see a more traditional spring river rise. That would be good for rainbow trout recruitment, which has fallen.
“Rainbows don’t like big water years,” Ruggles said.
That’s because they spawn in the spring. High water can scour eggs out of the spawning gravel and flood small side channels where young fish can hide from larger predatory fish during years when the river flows are lower.
Steady stream flows over the winter should ensure a good brown trout hatch, Ruggles said. Brown trout spawn in the fall. High water has scoured spawning gravels free of silt, making for better egg-laying conditions.
“We should see good recruitment,” he said.
More normal river flows could also mean fewer spillway releases from the dam, which would translate to cooler water with less turbidity that benefits the fishery and anglers.
Unlike its counterpart in Montana, the Bighorn River fishery above the reservoir in Wyoming has benefited from high water years. Native sauger populations are flourishing.
“Cooler water temperatures are probably more beneficial for higher recruitment, but that’s probably not the only thing going on,” said Joe Skorupski, fisheries biologist for the Wyoming Game and Fish Department.
Sampling of the fishery showed sauger — which resemble walleye but are native to the Bighorn River — were averaging 19 inches last fall.
“For sauger that’s pretty exceptional,” Skorupski said. “We see fish routinely that are well over 20 inches. That’s the largest we’ve seen in a long time.”
The sauger population is built of some resident river fish, some resident Bighorn Reservoir fish and a large component of migratory sauger. The migratory fish will overwinter in the reservoir and swim upstream as far as 90 miles to Worland to spawn.
“This is a real gem for the Bighorn and the state,” Skorupski said. “There are a lot of fish, a lot of big fish and they’re native.”
Here’s the downside: the high water that’s good for the fish makes it tougher for anglers. That means a lot of the sauger harvest comes in the winter when anglers can fish through the reservoir ice.
“The big water years are great for the fish but not for fishing,” Skorupski said.
The upper Bighorn River is also home to shovelnose sturgeon, a once-native fish that died off after the river was dammed. The fish was restocked in the upper river beginning in 1996.
The question WGFD is now seeking to answer is whether the species can be self-sustaining. To do that, the sturgeon need about 60 to 150 miles of free-flowing, undammed water from where the eggs hatch and start drifting before reaching the reservoir. Oxygen-deprived water can kill the larvae once they hit the reservoir.
“I don’t know if we have enough drift distance,” Skorupski said, but a study is underway to answer that question.
Meanwhile the planted sturgeon have grown to around 5 pounds with a few ranging from 7 to 10 pounds. The state record shovelnose was caught in Bighorn Reservoir in 2014 by Clint Franklin, of Powell, Wyoming. That fish weighed 10 pounds, 4.2 ounces. So a new state record could be swimming in the river or reservoir right now.