Idaho Falls, Idaho – To Colorado anglers eager for a rainbow revival, the state of affairs on the South Fork of the Snake River below Palisades Reservoir might seem scandalous.
No limit on rainbow trout. Catch and keep all you want. Throw the rascals out.
This unusual directive is all part of a determined plan by Idaho Fish and Game to nourish and promote cutthroat trout, the native fish of a river that ranks among the finest angling experiences in the West.
“Rainbows pose a real threat to the cutthroat through hybridization, and it’s the cutthroat that makes this a world-renowned fishery,” said Jim Fredericks, regional fisheries manager.
Indeed, South Fork and cutthroat have become synonymous for serious anglers, at least in that canyon stretch below Palisades.
“These trout set up on riffles, and people can have 50- to 75-fish days,” Fredericks said. “The South Fork is the best large river for catching Yellowstone cutthroat trout.”
For those who don’t understand local geographic terminology and the peculiar biology of Snake River trout, that last sentence requires some explaining.
In Idaho, the Snake River below Palisades, just over the border from Wyoming, is known as the South Fork to distinguish it from the Henry’s Fork, which soon joins in from the North. Almost everyone else simply calls the big river the Snake. It’s an Idaho thing.
Then there’s the resolution of why the large-spotted Yellowstone cuttthroat common to the east side of the Continental Divide also is native to this section of the Snake, while the fine-spotted subspecies thrives in the upper river near Jackson, Wyo.
The large-spotted cutt has been in the Snake drainage, including the Henry’s Fork, since glacial times and continues to flourish below Palisades. Robert J. Behnke, whose landmark book, “Trout and Salmon of North America,” ranks as the definitive work on such subjects, explains it thus:
“How the two forms … maintain their separate distributions in the upper Snake River drainage is unknown, but they must have evolved differences in behavior and environmental preferences that reinforce their spatial separation.”
Anglers who flock here care only that the South Fork variety is consistently large, generally 16 to 18 inches, and relatively easy to catch using large dry flies. Who could ask for more?
To rid the river of the wretched rainbows, the wildlife agency also promotes heavy spring flows more beneficial to cutts, while also installing traps on larger tributaries to block rainbow invasions.
Rainbows maintain a stronghold immediately below the dam, while cutts reign supreme in the canyon. In a continuing development that bodes ill for a further extension of cutthroat territory, brown trout generally have taken over the lower river, from the Byington Boat Access to Idaho Falls.
“You rarely see a rainbow down here and not very many cutts, either,” said Scott Smith, who floats the South Fork about 30 days a year from his station at Jack Dennis Sports in Jackson.
On his maiden voyage with a new drift boat, Smith was working the stretch between Byington and Lorenzo. An early-season ramp closure caused him to miss the canyon and the cutts.
Now he was in brown trout territory, where deep-drifted streamers ruled the day. The fish were fat and feisty, but this was not the dry-fly action Smith has come to love at a place that rivals more famous western rivers, but with less pressure.
Like a man with a shopping list at his favorite store, Smith ticks off the coming highlights: a phenomenal caddis hatch just before Memorial Day; a salmonfly hatch that begins in mid-June near Idaho Falls and reaches Palisades about July 4; a companion flourish of pale morning duns and yellow sallies, mahogany dun mayflies and some form of caddis or smaller stonefly flitting about all summer.
“July is my favorite month, with lots of hatches and really crazy dry-fly fishing,” Smith declared. “If you can’t catch a trout on a dry fly in this river in July, you need to take up another sport.”
Charlie Meyers can be reached at 303-954-1609 or cmeyers@denverpost.com.
