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Water Wisdom: Bugs barely there



Pteronarcys californica is among a family of insects known as the stonefly. A favorite among anglers, the stonefly is a sensitive insect threatened by siltation and increasing water temperatures. CC PHOTO

Anglers report reduced hatches


The buzz on the river this summer is that local anglers have noticed changes in the abundance of aquatic insects and the timing of their hatches. 

“I think the biggest thing everyone is talking about is that the hatches have been really sporadic,” said Solomon Ohman, shop staff at Grizzly on the River. Ohman observed multiple insect orders emerging simultaneously, instead of thick clouds of a single taxon.

Ennion Williams, outfitter and guide for Big Sky Trout with 24 years of experience on the Gallatin, detected a diminished salmonfly hatch, in particular. 

“The bugs were there, but there weren’t any heavy hatches all at once,” Williams said, adding that high water and cooler temperatures coupled with last summer’s algae bloom could have impacted salmonfly emergence this year.

Although a few studies have linked environmental changes with shifts in the life cycle of aquatic insects, this is still an area of active research, according to Sean Sullivan, an aquatic ecologist with Rhithron Associates, Inc. With those limitations in mind, Sullivan suggested a few factors unique to this summer that may be linked to the observations of local anglers. 

Summer started slowly this year with a cold, wet early July when compared to the past couple of years. Air temperature in the beginning of the month was, on average, a few degrees below normal. The number of days above a certain temperature drives the hatches of many insect species, thus cool weather could limit their emergence. 

Due to many days with precipitation, streamflow at the Gallatin Gateway gauge has been slightly above average since last October with water levels climbing into the 75th percentile—25 percent above average—early last month. High spring flows sustained into the summer could suppress emergence because insects have remained in their springtime refuge later into the season.

Finally, nuisance algae growth from recent years that lingers in the channel could impact both habitat and dissolved oxygen levels to the detriment of insect populations.

Local conditions are superimposed over a statewide trend. Research by the Montana Natural Heritage Program reported broad declines in salmonfly distribution across Montana. These sensitive species were first threatened by dams and mining. Within the past 30 years, siltation and increasing water temperatures have started to impact their abundance.

In addition to these factors, the response of insects to environmental changes depends on the species in question. Due to the fact that three species in the salmonfly (Pteronarcyidae) family are native to Montana, scientists need more data to accurately explain fluctuations in the life cycle of these aquatic insects. 

“There is a growing recognition that the fly-fishing community has a unique opportunity to provide data to help validate any observed trends in phenological shifts,” Sullivan said. He encouraged river lovers to contribute their knowledge to an iNaturalist project called “The River’s Calendar,” which is designed to document emergence periods for the aquatic insects of North America. 

Despite the salmonfly shortage, Jay Markevich, shop manager for Gallatin River Guides, reported that the fishing is still good, speculating that both the size and quality of fish caught on the Gallatin increased this summer. 

Stephanie Lynn is the education and communications coordinator for the Gallatin River Task Force.

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