Fish Facts: Bonneville Cutthroat Trout (Oncorhyncus clarkii utah)

The state fish of Utah, the Bonneville cutthroat trout (Oncorhyncus clarkii utah) is a survivor, having endured a geological cataclysm—which splintered the population—as well as a century of habitat loss caused by man. Like the greenback cutthroat, Bonnevilles were once thought to be extinct, but in 1974, biologists looking to document every wildlife species in Utah discovered a remote remnant population of the subspecies in the headwaters of Birch Creek. Widespread recovery has occurred over the past four decades, and the subspecies is now found in Idaho and Wyoming, as well. Fly fishers have plenty of opportunities to catch Bonnevilles, which are one of the four subspecies of cutthroats that make up the Wyoming Cutt-Slam and the Utah Cutthroat Slam programs. They’re also part of the Western Native Trout Challenge.

Range and Species History

Before the Bonneville Flood, the range of Oncorhyncus clarkii utah extended throughout Utah, eastern Nevada, southeastern Idaho, and southwestern Wyoming. As the lake drained and the climate changed, desiccation reduced the once massive body of water to several large lakes, and the range of Bonneville cutthroats shrank along with it. In the process, populations became isolated from each other. Dr. Robert Behnke describes four distinct geographical groupings: those found in the main Bonneville Basin, in the Snake Valley along the Utah-Nevada border, in the Bear River drainage, and in Bear Lake. Each population has a distinct appearance, and some even display different numbers of gill rakers and teeth.

Bonneville cutthroats are relative late-comers on the evolutionary chart, having originated between 50,000 and 100,000 years ago. (In contrast, the first Lahontan cutthroats appeared about 1 million years ago.) According to Behnke, the genetic evidence suggests that Yellowstone cutthroats were the Bonnevilles’ forbears. And as you might imagine for a species that evolved around a massive lake, there are both riverine and lacustrine populations. River-dwelling Bonnevilles live and behave much like cutthroat trout everywhere, but the cutthroats of Bear Lake live longer and are considerably more predatory, with adults feeding especially heavily on the Bear Lake cisco.

After the species was rediscovered in 1974, several more pure-strain populations were identified, and these formed the basis for extensive restocking and transplanting efforts. In 2008, the US Fish and Wildlife Service performed a review of the status of Bonneville cutthroats throughout their range and determined that no special listing was required. Biologists are keen to maintain the separate genetic stocks, however, and are careful about where they plant each strain. In many situations, a stream is first chemically treated with rotenone to remove all potential competing species before Bonnevilles are introduced. As a result of these programs—which often include combinations of state, federal, and private entities—Bonneville cutthroats now swim in about 2,500 miles of streams across the four states.

The Bonneville Flood

Bonneville cutthroats are named for Lake Bonneville, a massive body of water that filled the eastern part of what is now known as the Great Basin. Nearly as large as Lake Michigan and more than 1,000 feet deep, Lake Bonneville held the first lacustrine populations of the cutthroat subspecies, with stream-dwelling populations filling the tributaries. About 14,500 years ago, the lake breached at Red Rock Pass, Idaho, releasing a torrent that was 33,000,000 CFS at its peak. With a change in climate, the lake eventually dried up—leaving Great Salt Lake, Utah Lake, Sevier Lake, Rush Lake, and Little Salt Lake as remnants—and isolating cutthroat populations from each other, which explains some of the differences in appearance of Bonneville cutthroats from different watersheds.

The Importance of “Red Fish”

The oral history of the Goshute tribe of the Western Shoshone, who inhabited the Deep Creek Mountains on the Utah-Nevada border, contains stories of the “red fish” that once filled little streams throughout the region, and the Mormons and other pioneers who settled the Great Basin were saved from starvation on more than one occasion but Bonneville cutthroats. But soon after settlement, the usual suspects—water diversion, overgrazing, overfishing, and the introduction of nonnative fish species—began destroying the trout’s habitat. In 1864, one haul of a commercial fishing net produced 3,500 pounds of trout in Utah Lake. By 1930, just a single Bonneville cutthroat was caught during the entire fishing season. Restoration efforts saw the number of populations in Utah rise from just six in 1978 to 261 in 2000, and Wyoming, Idaho, and Nevada are also working to bring the species back.

Tactics and Flies

Even among cutthroat trout, which are not credited with extreme wariness, Bonnevilles are considered pretty gullible—which may partly explain how they were nearly wiped out so quickly. But they do requires certain conditions, so once you’ve found a stream that contains the species, look for stretches with cool, oxygenated water and a healthy stream riparian zone, which provides structure, cover, shade, and bank stability. The fish are avid insect-eaters, but larger specimens will also eat baitfish. Usually, all you need to catch Bonnevilles is a small collection of generalist dry flies (Parachute Adams, Elk-Hair Caddis, and terrestrials), nymphs (Hare’s Ears, Pheasant Tails, and Copper Johns), and streamers (Woolly Buggers, Muddlers, and Mickey Finns).