Viewed by many trout anglers as a “trash fish,” the mountain whitefish has been unfairly maligned and is actually an excellent fly-rod quarry.
Many a fly fisher has been disappointed to discover that the fish fighting on the end of his line is not a trout, but a native mountain whitefish (Prosopium williamsoni). As many guides will tell, however, “Whitey” has saved many a troutless day on some of the West’s most famous rivers. One reason for this is that whitefish outnumber trout by 10 to 1 in many waters, and they are eager to take fly.
What’s in a Name?
The belief that whitefish compete with trout for food is widespread, but they generally feed farther down in the water column¬¬—often right on the bottom—and inhabit lower stretches of pools. Young whitefish also provide forage for larger trout, especially browns. It’s important to note that it is the browns that are the nonnative invaders in this situation. In fact, Meriwether Lewis described the mountain whitefish as a “bottle-nosed fish” when he saw it in the upper Missouri drainage in 1805—some 80 years before the first browns came to these shores.
Range and Life History
The original range of the mountain whitefish extends from the headwaters of the McKenzie River in Canada’s Northwest Territories to Green River basin Utah. They also inhabit the drainages of some Pacific coastal rivers of British Columbia, such as the Stikine and Skeena, as well as western Washington State. The confluence of the Missouri and the Yellowstone is the easternmost limit of the range.
Whitefish spawn in fall, gathering into huge groups that can cover the streambed in places. They do not dig redds, like trout or salmon; instead the eggs disperse into the gravel substrate. These eggs provide meals for hungry trout. In larger rivers, whitefish sometimes migrate with the seasons to different parts of a river system. The small, downward-turned mouths of whitefish are specialized for vacuuming up zooplankton and other tiny, bottom-dwelling organisms. They do occasionally rise to insects on the surface, especially in slow-water sections of a river.
Mountain whitefish can live up to 18 years, and one specimen caught in Alberta was determined to be 29 years old. In recent years, anglers on Montana’s Madison River have noted a steep decline in whitefish populations, and biologists are at a loss to explain it. One theory identifies whirling disease as the culprit. Because whitefish evolved alongside trout, they are a vital part of the ecosystem of rivers such as the Madison, a recent study was launched to assess the problem.
Tactics and Flies
Mountain whitefish average 12 to 14 inches and rarely grow larger than 20 inches. The all-tackle world record, caught from the Columbia River in 1983, weighed 5 pounds, 2 ounces. Because whitefish are bottom feeders, nymphing is the best way to take them on a fly, and anglers fishing a dry-and-dropper rig for trout usually hook whitefish on the nymph underneath the surface pattern. On larger rivers, such as the Yellowstone, it’s hard to beat a size 12 Prince Nymph, while on smaller water’s you’ll want to go smaller (sizes 14 to 16) with Pheasant Tails, Hare’s Ears, and Copper Johns.