Bigger Is Better

The Latin name for brook trout, Salvelinus fontinalis, means "speckled fish of the fountains," but a new study by researchers in the college suggests, for the first time, that the larger streams and rivers those fountains, or headwaters, flow into may be just as important to the brook trout.

With few exceptions, brook trout are now found only in small mountain streams that stay cold enough year-round to meet their biological needs, below 68 degrees Fahrenheit. Many had assumed those headwater habitats alone were critical for their survival.

But a genetic analysis of brook trout in streams across the 460-square-mile Loyalsock Creek drainage in northcentral Pennsylvania shows that the fish are very similar genetically, suggesting close relatedness among populations. The only way that could have happened, according to postdoctoral research scholar Shannon White, is if the fish moved between tributaries in the 86-mile-long Loyalsock Creek.

Researcher Shannon White clips a caudal fin on a brook trout from a small tributary of Loyalsock Creek. Photo by Tyler Wagner Research Group/Penn State.

From approximately June through September, temperatures in Loyalsock Creek exceed the brook trout's thermal tolerance, White pointed out, so fish are believed to inhabit only the bigger river system during the winter. Although the behavior and survival of brook trout in Loyalsock Creek are not well understood, researchers hypothesize that 20 percent of brook trout move into the mainstem, or principal watercourse, after spawning in a tributary in October or November and stay until late spring, when some swim up new tributaries.

To build what White called "a family tree" of brook trout in the Loyalsock drainage, the researchers collected 1,627 adult brook trout from 33 sites. They clipped the caudal fins of those fish and conducted a genetic analysis on those tissue samples. The findings were published in Ecological Applications.

--Jeff Mulhollem