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Wildfire's long-term effect on fish unknownThe Derby Mountain fire burned hot enough in some spots to kill and cook trout right in the streams. But the worst effects of the big fire on area fisheries may be yet to come.
What blaze didn't kill directly, moisture on burned slopes could
The rampaging wildfire, which has burned more than 207,000 acres, scorched through creek drainages - Upper Deer Creek, Lower Deer Creek, Bridger Creek, Bad Canyon Creek and smaller waters that feed into the Boulder, Yellowstone and Stillwater rivers.
"If the fire burns hot enough and the creek is small enough, it will cook the fish. It will kill them," said Jim Olsen, fisheries biologist for Montana Fish, Wildlife and Parks. "It all depends on the water and the fire.
"Darin Watchke, the Forest Service fisheries biologist, walked Bad Canyon Creek and there were places where it did burn hot enough to cook the fish," Olson said. "Fish were dead in some spots. In other spots, the fish were fine.
"But that area didn't burn as hot as some of the others," Olsen added. "Lower Deer Creek has a good cutthroat population, along with some brown trout, and it burned really hot. The same with Upper Deer Creek and its cutthroats and brook trout."
The extent of the damage to the fisheries won't be known until fire crews declare the area safe and Forest Service and FWP biologists can go in and survey the streams.
In definite jeopardy are cutthroat trout restoration projects done on Bad Canyon and Lower Deer creeks. These projects were done to return native cutthroat trout to those waters.
If the fire didn't kill the fish immediately, there's an even larger threat looming when rain or snow cover the countryside.
"With the area burned off, we don't know what exactly is going to happen with precipitation," Olsen said. "If we get a lot of rain, the burned dirt can't hold the moisture. It really runs off easy. You can get big ash flows and debris flows into the water.
"Those flows really put the pH (alkalinity) levels high and makes the water itself toxic and makes oxygen levels go down," he said. "That can kill the fish, too. That's especially true in the small creeks. In the bigger rivers, it might be diluted enough.
"If we get a nice, gentle slow rain this fall, we might be OK. That will help to compact some of the soils again and get the microbes started that build soil," he said. "But it will be an unstable situation from now through snowmelt next spring."
A similar situation hit Crooked Creek in the Pryor Mountains in the wake of a wildfire there, said Ken Frazer, FWP fisheries biologist in Billings.
"There was nothing to stop the runoff," Frazer said. "We had a 100-year rain after the fire and it we got huge sediment flow into the stream and it took a lot of the fish. It took out half of our cutthroat trout population and most of the brook trout.
"It took pretty much everything in the mudflows going downstream on Crooked Creek including the bugs," he said.
Olsen is hoping for the best in regard to the fisheries affected by the Derby fire.
"This happened on Lower Deer Creek during a fire in the late 1980s or early '90s," Olsen said. "That fire burned all of the West Fork. It flooded out and really knocked the fish population back.
"Within seven or eight years, the fish were back at levels where they were before the fire," he said. "But that was just one fork of one creek. This is a much larger area with a larger area burned and more waters that can be affected.
"As soon as they get the fire out, we're going to go in and see what's left of the fisheries," Olsen said. "After that, it's all weather dependent. We might be just fine. We might not. We'll just have to see."
Gazette outdoor editor Mark Henckel can be contacted at email@example.com or at 657-1395.
Page Updated: Thursday May 07, 2009 09:14 AM Pacific
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