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Trout populations survived fires

The fires' effects on trout and people

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Fisheries biologists have monitored streams for fish kills in many tributaries of the Bitterroot River, and have come up with some good news: Last summer’s fires didn’t have a great impact on trout populations.

Mike Jakober, a fisheries biologist with the Forest Service’s Sula District, conducted trout population surveys on several streams that were hard hit by the fires: Laird, Reimel, Rye, Skalkaho, Sleeping Child, Blue Joint, and others.

In areas that burned hot, fish kills were naturally higher, but only in stretches of anywhere from 100 feet to four miles, Jakober says. In areas where the blazes were moderate to low there was no real change in trout populations.

“So it was real patchy,” he says. “You’d go along Laird Creek and there were obvious fish kills.”

Why trout died, however, can only be guessed at. “That’s not really been pinned down,” he notes.

It may be the fish died from high water temperatures caused by fires blazing through the riparian area, or it could be that ash changes the chemical composition in the streams.

A water temperature gauge had been placed in Laird Creek prior to “Black Sunday” of Aug. 6, when several homes there were destroyed by fire. The gauge recorded the water temperature every two-and-a-half hours, so Jakober was excited about what he thought was a “real score”—accurate water temperature readings in the midst of a firestorm, and possibly an answer to the question, why do fish die in wildfires?

Alas, the gauge recorded average water temperatures on Aug. 6. It may be that there simply was no change in the water temperature when the fire consumed Laird Creek. Or it may be that the fire burned so hot and fast that the water temperature rose quickly, poaching the fish between readings.

“It may have been we were just unlucky,” he says. “It could have come through so fast we could have missed it.”

The “take-home message,” Jakober says, is that the fires, regardless of how hot they burned in some areas, did not destroy entire trout populations in any of the streams monitored.

If an affected habitat was in good shape before the fires, it will probably take three to five years before the fishery fully recovers.

The next potential problem for the Bitterroot River and its tributaries is the spring runoff. So far, Jakober hasn’t noticed any excessive turbidity in any tributaries, not even the hard hit ones, and not even after the fall rains.

Whether the streams will continue to run clear after the summer fires will depend on spring weather.

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