Fisheries biologist Ladd Knotek scanned the trout resting in his oversized net settled among the rocks of Rattlesnake Creek. He reached for the only dark head he saw. It was a brook trout, not the hoped-for bull.
Turning away, Knotek waded back to where fisheries technician Caleb Uerling was sweeping a series of pools with an electroshocking wand. Big Sky Watershed employee Grant Flaming and volunteer Tim Hall stood just downstream, fishing nets at the ready.
They had gathered on a cool, cloudy Friday morning near the horse bridge in the Rattlesnake National Recreation Area. The goal of the Montana Fish, Wildlife & Parks crew was to survey a 600-yard stretch of Rattlesnake Creek for every fish they could find, not the easiest task.
But Knotek knew what to do.
He has sampled three sites along the creek every three years since 2004. The bridge stretch is the farthest downstream. He knows what fish have been there, and what he wants to find. But this time, he didn’t find what he wanted.
“The Rattlesnake is a beautiful wild-trout stream with good, remnant native-trout components that we hope to bring up,” Knotek said. “But the migratory (bull trout) population of the Clark Fork is pretty much gone.”
Suddenly, a flash of silver erupted from the water as a juvenile trout tried to escape Uerling’s electric current. Others that weren’t as lucky popped up to float downstream on their sides, mouths gaping. Below the surface, dark shadows shot between the rocks.
With shouts of “Get ‘em,” and “There’s a good one,” the netters went to work trying to snag stunned or sneaky fish. After each swish, they’d search the bottom of their nets for young trout, some as small as 2 inches.
Those little guys just hatched in the creek this year. The larger juveniles were 2 to 3 years old, and a few of the biggest were 7 inches long.
(The electric current from the wand stuns fish just long enough to give the crew a chance to catch them. They’re back to normal after a few minutes.)
By noon, the crew had netted about 130 fish, about the average number that Knotek usually gets, although this was a good year for the amount of water in the creek. Among the trout were a handful of sculpin and tailed-frog tadpoles, both indicators of clean water.
The thing that disappointed Knotek was the absence of bull trout. But he also wasn’t happy that nonnative fish, particularly brown trout, accounted for about half of the fish he caught.
Native bull and westslope cutthroat trout need cold, clean water, while brown, rainbow and brook trout are not native to Montana and are able to tolerate warmer water.
And based on Knotek’s surveys, brown trout are slowly moving upstream.
The horse bridge site has held a few brown trout since at least 2004. But it also used to have bull trout. In 2007, Knotek found more than seven times as many bull trout as brown trout. That ended in 2010. Since then, the percentage of brown trout has climbed from 5 percent to almost 50 percent. The rest are westslope cutthroat trout hybrids with a few nonnative brook trout.
“Brown trout work their way in. It’s not displacement – it’s replacement. You see bull trout fade out and retract, and brown trout move in,” Knotek said.
At the two sites farther upstream, bull trout seemed to hang on with about 10 percent of the population. But this year, Knotek found none, even though the East Fork of the Rattlesnake sends in cooler water farther up.
“It’s always been on the edge as far as temperature. Bull trout need temps in the low 50s to low 60s,” Knotek said. “It’s starting to push past that now.”
He’s been watching brown trout move into several tributaries of the Clark Fork River as climate change has modified stream characteristics, causing bull trout to retreat or die out.
South-facing streams like the Rattlesnake warm faster. But climate change has also caused spring runoff to occur earlier, and often there are two peaks, and their timing can affect spawning.
“It’s really messing with them,” Knotek said. “ Any watershed that has temperature issues or heavy (forest) management issues, we’re seeing the same thing. Gold Creek – don’t know if we can find bull trout in there anymore. Petty Creek – they’re gone. The streams that don’t have high resiliency – they’re tanking.”
Fortunately, Rattlesnake Creek is still home to bull trout way up in the headwaters, beyond a big waterfall that keeps brown trout from invading. But it also traps the native trout above, so they no longer migrate.
Knotek would like to see bull trout return to the lower reaches, but it’s pointless if the stream water keeps warming. Any bull trout that ended up there would likely die.
That could change if the city of Missoula and the U.S. Forest Service can work with FWP to release water from the upper lakes each summer. They ran a small test this summer when they released some water from Big Lake and measured the resulting temperatures downstream.
Add water from a couple of lakes together and Knotek thinks there’s the potential to moderate the effect of summer heat on Rattlesnake Creek. But for now, Knotek will have to just keep counting fish and hope a few bull trout can hang on.
“It’s a microcosm of what’s happening region-wide. This drainage is so important because there are few places left with viable bull trout populations, and this is the closest to Missoula,” Knotek said.