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Wildfires can be a boon to fisheries

Fishermen need not fear the impact of fire on their sport.

But they need to keep their guard up when humans want to fiddle in their favorite mountain streams.

The St. Joe River, Kelly Creek, Fish Creek and other waters in Idaho and Montana are famous for their thriving native populations of bull trout and westslope cutthroats because of – and despite – major forest fires.

Idaho Fish and Game Department research confirms that native fishes, especially those that can migrate, are well-adapted to big 100-year or even the 500-year fire events.

While hot fires can bare the ground, change soil composition and temporarily foul stream sections with sediment, “they also tend to add a lot of large woody debris to stream channels,” said Chip Corsi, Idaho Fish and Game Department regional manager in Coeur d’Alene.

The logs create scour areas that expose the clean and larger gravels important for spawning, incubation, and fry rearing as well as for insect production, he said.

“Large wood also provides lots of cover and channel complexity that fish such as bull and cutthroat trout have an affinity for,” he said. “A lot of deadfall can provide a fair bit of shade to protect stream temperatures.

“And fire often delivers nutrient pulses that can stimulate primary productivity, making more bugs and other fish food.”

Intense fires, such as those in 1910, can kill fish in some areas by raising water temperatures.

But if the fish have a history of migrating, and the drainage is not otherwise impaired, fish will return to spawn in following years, he said, citing the most recent fisheries studies following the intense 1990s fires near Boise.

Native fisheries – more specifically “healthy” native fisheries – are adapted and resilient to natural events such as intense forest fires, he said.

“Had the migratory component of those fish populations been impaired for other reasons – migration barriers, over-fishing, de-watering, pollution, and so on – the likelihood of recolonization, and hence resiliency, goes way down.”