But I Thought the Science was Settled!

Rivers and large streams more important than previously thought for brook trout

Rivers and larger streams are more important than previously thought to brook trout, which are generally assumed to be more associated with small mountain streams, according to research by Penn State.

Under assault from a warming climate, most wild brook trout in the U.S. are now found in those small mountain streams, which stay cold enough year-round to meet their biological need for temperatures below 68 degrees Fahrenheit.

But a genetic analysis of brook trout in streams across the 460-square-mile Loyalsock Creek drainage in northcentral Pennsylvania has shown that the fish are similar genetically, suggesting close relatedness among populations.

The only way that could have happened, according to Shannon White, postdoctoral scholar in the College of Agricultural Sciences, is fish moving between tributaries in the 86-mile-long Loyalsock Creek.

Temperatures in Loyalsock Creek exceed brook trout thermal tolerance from approximately June through September, 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 some brook trout move into the mainstem after spawning in a tributary in October or November and stay until late spring, when some swim up new tributaries.

“It’s pretty simple — if widespread populations are related genetically, it indicates that fish are moving around between those populations,” she explained. “There’s a high degree of genetic connectivity between populations separated by the mainstem, and that indicates that brook trout are swimming into Loyalsock Creek and using it as a movement corridor to connect populations in other tributaries.”

Fish swim? Whoda thunk?

The Wombat delivers Rule 5 Sunday: Park Hye-su as promised.