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Research project trying to solve "fish mystery" on Rock Creek in Missoula

Posted at 8:00 PM, Mar 24, 2021
and last updated 2021-03-24 22:00:17-04

MISSOULA — Researchers are hoping the final year of a four-year study will help solve a "fish mystery,"which could provide answers to save one of western Montana's most unique species.

Next to the Blackfoot River, Rock Creek east of Missoula is probably one of the most legendary western Montana fishing destinations. From headwaters deep in the Sapphire Mountains to the confluence with the Clark Fork, Rock Creek is a favorite for anglers. But it also holds a puzzle. A rare native run of Westslope Cutthroat Trout.

"So we've started looking at, why is that? Especially because we know there's also a concurrent rainbow trout fishery in Rock Creek and their spawning seasons are next to each other and that's where you get hybridization. So how come we have pure cutthroat trout and we also have rainbow trout," observes Tess Scanlon, the Rock Creek project coordinator for Trout Unlimited.

Tuesday afternoon, MTN News was invited to join Trout Unlimited and biologists from Montana Fish, Wildlife and Parks as they were electroshocking and "tagging" some of the hybrids. Scanlon said the focus this outing was on the hybrids.

"The study in the last two years has been trying to look at where the differences are in spawning so that we can better understand how we still have a genetically pure cutthroat trout population that we'd like to protect into the future," she said.

It's a tricky operation, essentially shoreline surgery, as the trout are knocked unconscious and in minutes, a tag is inserted, and the stomach slit closed as its gills are continually bathed in fresh water to prevent suffocation. The research is different from some of the other tagging projects we've seen in local streams, using radio identification tags.

Bill Pfeiffer, outreach coordinator for the Westslope Chapter of Trout Unlimited, says the group has been funding two studies, radio tags, and one using a "mark recapture study".

“And that's where we mark the fish, we release them and then we get information back from them when other people recapture them, hopefully anglers. With the Race Up Rock Creek this is a different type of study. We're actually putting radio transmitters into the fish and then tracking them in, you know, essentially in real time, to see where they're at.”

Biologists use receivers to locate the radio-tagged trout within half-a-mile. And you can follow along too. The tagged fish get their pictures taken and will be posted on the Westslope Chapter of Trout Unlimited's website for adoption as a fund raiser.

“We're able to see exactly where the fish are, as opposed to making inferences. We can, you know, know exactly where these fish are as soon as we, get that reading back from them from the radio tag," Pfeiffer explains.

The radio tagging is just one of several steps Trout Unlimited is taking to improve the Rock Creek fishery. Donors are also helping to pay for other steps to remove blocks to fish passage, such as removal of old bridges and small dams. For more on the project, visit the web page for the Westslope Chapter of Trout Unlimited.