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Water Wisdom: Buggin’ Out



An example of one of the many flies that can be observed while on the river in Montana summers. PHOTO COURTESY OF GALLATIN RIVER TASK FORCE


Walk into any fly shop and you’re likely to be overwhelmed with options. Nowhere does this ring truer than at the fly display cases. There are thousands of choices to make, and what you decide will be the difference between an epic day on the water and striking out yet again. 

On the Gallatin, to match the hatch (pick the right fly for where and when you’re fishing), you don’t need to worry yourself with the entire selection. Most of the upper river can be fished successfully with a few flies. 

While several major hatches are common, fishing with caddis, when fish are eating hoppers, might not lead to success. Not only do you have to select flies that hatch on our river, but you also have to pay attention to time of year, weather on a given day, cloud cover, sunshine, and water temperature. Is it early morning or mid-day? Did it rain last night? All these factors influence the timing of hatches and when fish might be feeding on a given bug.

Now that the river is running clear, dry-fly season is upon us. Dry flies drift on the surface and entice fish to feed where you can see them. In July, classic dry-fly patterns like Chubby Chernobyls, Royal Wulffs and Parachute Adams are all effective. Try different colors and sizes until something clicks. 

While paying attention to the hatch could make or break your day on the water, what bugs are out there and in what numbers could also tell us important information about changing land-use patterns, and how that land use is impacting water quality. 

“Urbanization has known effects on invertebrate populations,” says Sean Sullivan, an aquatic ecologist with the environmental consulting firm Rhithron Associates in Missoula. “We see loss of riparian habitat and an increase in sediment loads.” As Sullivan notes, this shift in habitat can cause some invertebrates to move on, and new species fill the void.

For now, we don’t know what these changes portend. “We don’t have the data,” says Sullivan. This is where anglers come in. “Citizen science will be important. Anglers have to become active observers of what’s out there,” he continues. “So far, we don’t have a canary in the coal mine, but speaking generally, there is more of a holistic shift in the invertebrate community.” 

While it might not be possible to make specific conclusions about how urbanization is playing out in Upper Gallatin Watershed regarding specific bug populations, we do know that shifts in invertebrates lead to shifts in fish and fish behavior. “Trout species are drift feeders. If we don’t have the same numbers of biomass drifting, trout will move,” Sullivan said. 

Again, this scenario is shown through data gathered elsewhere, and comparing one watershed to another has its limitations. We do know that as land in Big Sky continues to be developed, we should expect changes in wildlife behavior, from charismatic megafauna like grizzlies to tiny insects like caddis. These changes will have ripple effects that spread throughout the watershed, from the high alpine to the river’s bottom. “Anglers can contribute by recording information,” says Sullivan. “Who’s hatching, specifically? What species of mayfly and when?” 

As it seems, matching the hatch has more benefits than just landing a big rainbow. If we’re spending all summer on the river, our observations about insect behavior can catch us fish, but they can also help plan for a more sustainable community, a community focused on water quality and fisheries health.

David Tucker is the communications manager for the Gallatin River Task Force. 

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