FORT SMITH — If Mike Ruggles had a magic wand and could make the Bighorn River’s flow perfect for rainbow and brown trout, he would keep it at 2,500 to 3,500 cubic feet per second.

Ruggles is a Montana Fish, Wildlife and Parks fisheries biologist who oversees the Bighorn. According to his figures the Bureau of Reclamation, which manages water flows into the Bighorn River from Yellowtail Dam, has hit his ideal target range about 39 percent of the time since 2009. That’s when the Bureau drafted new operating criteria.

“What we really run into is the times over 8,000 cfs, which is 17 percent of the time,” Ruggles said while addressing the Bighorn River Alliance, a river and angler advocacy group, last Wednesday in Fort Smith.

At those flows, fewer people are coming to the small community of Fort Smith to fish, rent boats and stay in lodges — a money generator that has been estimated to dump roughly $40 million to $45 million a year into the local economy.

“This little part of the world gets tremendous fishing pressure,” Ruggles said.

FWP has estimated the river records about 180,000 angler days a year, a number comparable to rivers like the popular Madison or Missouri, but those rivers can spread anglers out much farther than the 12 miles of water that is the most heavily fished on the Bighorn — between the Afterbay Dam and Bighorn fishing access sites.

“It’s not all bad,” Ruggles told the crowd of about 75 people.

The higher flows tend to favor brown trout, which spawn in the fall. At the last count in 2016, the four miles of river below Three-Mile fishing access contained 2,500 brown and rainbow trout over 8 inches. Between 1992 and 2015 that same stretch of water averaged about 4,200 trout per mile.

Looking back for comparision, populations reached a high of about 2,300 rainbow trout per mile in 1997, and more than 8,800 brown trout per mile in 1998.

In response to a question, Ruggles said the water can only support so much biomass of fish — either a lot of smaller fish or a fewer number of bigger fish. Right now that biomass is “trending about the same,” Ruggles said, meaning the fewer fish are fairly fat.

“Those fish we caught last fall were hogs,” he said. “Thick, stocky fish.”

The next stretch upriver is where Ruggles has documented problems with retaining rainbow trout. High water flows mean more nitrogen in the water below Afterbay Dam. High levels of nitrogen can kill small rainbows that may be running upriver seeking a place where there are fewer fish, and therefore fewer predators.

“We do have a nitrogen problem, especially below Afterbay,” said Anne Marie Emery, executive director of the Bighorn River Alliance. “It’s a big puzzle, and the river is responding in ways we don’t understand.”

To complicate matters, in 2014 the river dropped in the spring leaving rainbow eggs high and dry right when they were about to hatch. Later that same season, the Bureau of Reclamation bounced flows upward again after heavy spring rains increased runoff.

“For me as a fish manager it was very frustrating,” Ruggles said.

Since then, Ruggles has lobbied the Bureau of Reclamation to be more considerate of the rainbow trout hatch. He said he’s hoping the agencies can work it out, given a few more attempts. Right now, though, things are tough for the nonnative fish that live in a manmade river environment.

“It’s kind of a perfect storm for rainbows on the Bighorn,” Ruggles said.

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Montana Untamed Editor

Montana Untamed editor for the Billings Gazette.