SWAN VALLEY — Crystal clear creek water rushes down the canyons along the South Fork of the Snake River in June. Snowmelt changes the speed and the temperature of the water in a hurry. The change is drastic enough to attract trout. They point their spotted noses upstream and start swimming.
“It is really amazing what fish can do when they’re trying to go spawn,” said Brett High, Idaho Department of Fish and Game fisheries biologist. “We’ve seen fish hold their positions almost vertically in a waterfall for several seconds. When they put their mind to it, they can go through some pretty incredible obstacles.”
One obstacle the thousands of spawners face is a fish trap and they won’t pass it without a helping hand.
Biologists in brown waders provide the hands. They work the waist-high water mid-June through mid-July. They sort fish at the traps on the tributaries of the South Fork of the Snake River. Native cutthroat trout swim up four tributaries along the main channel to spawn. Idaho Department of Fish and Game makes sure those fish make it to their spawning beds without rainbow trout joining them.
“Letting the rainbows stay (in the spawning run) would result in the disappearance of our native Yellowstone cutthroat trout,” High said. “Universally over time, the cutthroat lose that battle and are replaced by rainbows and hybrids and they are no more.”
The fisheries division started manually sorting spawners on the South Fork in 2001. It’s one of the many efforts to help native cutthroat in the river while keeping non-native rainbows from cross breeding with them. Rainbows spawn around the same time cutthroats do and they can hybridize with cutthroat because they’re closely related. Separating fish on their way to spawn reduces hybridization.
Cutthroat trout are recorded at the fish trap then sent upstream. Rainbows and hybrids are scooped out and sent to the kid’s pond in Victor so they don’t spawn in the same beds as cutthroats. “It doesn’t take too many of those slipping pass your weir to cause problems,” High said.
Another change in the last decade is the number of fish reaching the tributaries to spawn. Diversion improvements and barrier removal have increased the average number of returning spawners. That helps keep cutthroat from pulling a disappearing act.
“That’s something we don’t want to see happen,” said Matt Woodard, Trout Unlimited home rivers project manager. “I think it says something about Trout Unlimited and it says something about society in general when we let a particular species like cutthroat trout go away. I think to let that slip away, that’s the wrong thing to do.”
Woodard is sitting on an overturned bucket with a clipboard on his knee. He records the fish type and length as High calls out readings from the measuring board. They’re both smiling. The trap is full of cutthroats. No rainbows. More than a decade of disciplined sorting is finally showing real results.
“It’s going to take constant effort to ensure that cutthroat stick around in the river,” High said. “One of the key things to make that possible are these fish traps. If we lose these tributaries to rainbow trout then we guarantee losing cutthroat from the river.”