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Intellect

Cutthroat science: Trout DNA hold ancient secrets of the Rockies

  • BYU ecologist Dennis Shiozawa unlocks an ancient history of Utah’s landscape written on cutthroat trout DNA
  • BYU partners with Utah Division of Wildlife Resources to identify native strains of cutthroat throughout the state

It would be hard to blame BYU undergrad Andrew Anderson had he decided to keep the large, brightly colored cutthroat trout he hoisted from a local mountain stream.
Instead Anderson practiced a partial form of catch-and-release that would leave seasoned anglers scratching their heads. Before returning the fish to water to swim another day, Anderson snipped a piece of tail fin and tucked it away in a plastic sandwich bag full of ice.

Of course, you don’t need much of a fish if you only want its DNA.

Anderson is on the errand of BYU professor Dennis Shiozawa, an ecologist working to preserve a fish whose genes contain a history of Utah’s ancient landscape.

Native cutthroat trout, named for the signature orange slash marks near the gills, swam over and around the Rocky Mountains for millions of years before the pioneers made the journey by land.

“We do have a legacy here that we really ought to preserve,” Shiozawa said. “The Utah cutthroat was one of the major food sources that helped the early Saints survive the grasshopper famine in the Salt Lake Valley and Utah Valley.”

All other species of trout familiar to Utah anglers came in the 1880s as transplants courtesy of groups like the U.S. Fish Commission. Rainbow trout hail from the Pacific Northwest, brook trout from the Northeastern states, and brown trout from Europe.

The competition with introduced species is part of the reason why some types of cutthroats vanished in the 20th century.

State wildlife officials would like to preserve the remaining native populations, but it’s not easy to tell apart native and transplanted cutts – not to mention rainbow-cutthroat hybrids.

That’s the purpose of a partnership between the Division of Wildlife Resources (DWR) and BYU biologists like Shiozawa. Using mitochondrial DNA markers, the research group traces the ancestry of fish tissue collected all over Utah.

BYU’s analysis informs the state’s management plans for particular streams and lakes. In March Shiozawa and fellow BYU professor R. Paul Evans identified the first population of Greenback cutthroat found in Utah. The Greenbacks in Beaver Creek, which runs off the LaSal Mountains near Moab, may prove to be distant cousins left behind when most other Greenbacks migrated eastward to the front range of the Rocky Mountains in Colorado. The state issued an emergency rule change requiring catch-and-release fishing and banning the use of bait for that section of stream.

Recently Shiozawa also helped establish a brood stock of Colorado River cutthroats specifically for the north slope of the Uinta Mountains. Roger Wilson, the DWR’s sport fishing coordinator, reports that Bonneville and Colorado River cutthroat now occupy 35 percent of their historic range, which is better than they initially suspected.

“We try to establish patterns within subspecies to ensure we are putting appropriate fish in the right area,” Wilson said. “Genetic analysis is indispensable in developing a direction for our cutthroat restoration program.”

Sorting out natives, hybrids and transplants is the mundane part of the job, Shiozawa says. What really got him hooked (forgive the pun) on the cutthroat family tree are the clues it offers about the ancient history of the West.

“For instance, we know that cutthroats in the upper Colorado River basin are quite different from those in the lower Colorado,” Shiozawa said. “We can see in the cutthroat DNA that the upper Colorado River must have flowed somewhere else – perhaps to the north or northwest – before it established its current course and cut the Grand Canyon.”

The DNA from one population of trout also bears the tale of an ancient cutthroat migration to Northern Utah from a river basin that still flows to the Columbia River and into the Pacific Ocean. The itinerary went something like this: From the Snake River in Idaho take the Portneuf River exit, travel upstream and arrive at destination via the Bear River. The route no longer exists because a massive lava flow closed it off some 30,000 – 100,000 years ago, an event that sent the Bear River looping back into Utah where it presently drains into the Great Salt Lake.

“There are tons of little detective stories to work on,” Shiozawa said.

As for the students mentored by Shiozawa, some have taken their lessons in genetics into the fields of medicine and disease research. Anderson hopes to parlay his undergraduate ecological adventures into pediatric dentistry. And it’s not hard to imagine what kind of pictures would hang on the walls of “Doc” Anderson’s office.

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