Students catch trout in Big Elk Creek
Image Credit: ISU Photographic Services

Fishy Findings

Idaho State University researchers have discovered what sport fishermen have long suspected when they have hooked and are reeling in a trout: native cutthroat trout, a declining species, just aren't as strong as their competitors, nonnative rainbow trout.

ISU doctoral graduate Steven Seiler and biological sciences professor Ernest Keeley, Ph.D., measured the difference in the swimming stamina of cutthroat trout versus rainbows and cutthroat-rainbow hybrids. They raised Yellowstone cutthroat trout, rainbows and hybrids of the two species and tested their stamina by putting them in small tubes filled with water. They controlled the power of the water flowing through the tubes and measured the results.

"Our results suggest that introduced rainbow trout and cutthroat-rainbow trout hybrids can potentially out-compete native Yellowstone cutthroat trout through higher sustained swimming ability," Keeley says.

Besides being stronger, the shape of the rainbow trout's fins and body are more efficient for swimming.

Keeley's and Seiler's study is a one of a range of studies by researchers at various institutions aimed at determining how to protect native cutthroat species. In waters where rainbow trout have been introduced, the rainbows and hybrids are thought to have eliminated, threatened or weakened cutthroat populations by being genetically dominant when the fish interbreed. Rainbows are also proving to be hardier fish.

In another study, Keeley and Seiler found that rainbows and hybrids had the highest success over cutthroat of occupying and inhabiting the areas of streams that offer the best feeding opportunities.

This study suggests that juvenile Yellowstone cutthroat trout are less successful at maintaining profitable feeding territories and capturing food items when competing against rainbow trout and first generation hybrids.

Andy Taylor
ISU Magazine