Brook trout populations typically include some fish that hang out close to home and others that like to wander.
Photo: Pixabay
Human beings have a tendency to wander.
The Allman Brothers knew about all a ramblin’ man. Willie Nelson couldn’t wait to get on the road again. Jim Croce was rolling down the highway.
Shoot, even the B-52s knew everybody was movin’ and groovin’.
But brook trout?
Turns out quite a few of them like to travel, too.
Monitoring fish
Researchers at Penn State University put microchips in fish in several watersheds and monitoring their movement over the last several years. What they learned is that some wild brook trout are homebodies, while others are wanderers.
“There’s a high variability among fish. Some are movers and some are stayers,” said Tyler Wagner, assistant leader of the Cooperative Fish and Wildlife Research Unit.
“So we have some fish that might stay in the same pool for four months. And we have some fish that might move six and a half miles in a week.”
The fish often entered waters not considered brook trout friendly. It was not uncommon, he said, to see brookies go downstream in fall, when water temperatures had dropped, to enter what might be considered a smallmouth stream. They then ran up other tributaries, sometimes before turning around and going back.
Motivations
Stream flow is the number one factor that sparks brook trout to stay or go, Wagner said.
“Generally in the summer, low flows, these fish hunker down in pools,” he said.
By comparison, the onset of the spawn in fall sparks the largest “pulse” of movement.
“So there’s a definite seasonality to how much they move,” Wagner said.
Aside from that, there are other triggers.
Fish move more often in low gradient streams – those with little of slope – that in high gradient streams, too.
Size of the fish, though, doesn’t seem to make much of a difference.
“It’s not always that the big fish move and the small fish stay,” Wagner said. “It’s kind of unpredictable in terms of using size or weight of a fish to determine if it’s going to move a lot.”
How much they move is variable, as well. Some fish in one watershed, Wagner said, moved just 164 feet in four months. Others moved 5.6 miles.
Most, across all the watersheds examined, were more likely to move downstream than up.
Implications
Such knowledge is more than just trivia, Wagner said. It can help guide management decisions.
Knowing when and where fish move, for example, can show resource managers where they need to maintain “connectivity” between waters, he noted.
That’s important because healthy brook trout populations need both movers and stayers, he said.
“Those fish that like to take the risk to move are the ones that help maintain population connectivity and carry genetic material to neighboring streams. The cautious stayers are going to assure maybe higher survival. They’re not moving into a stream full of smallmouths nd brown trout,” he said.
Such diversity is going to be even more important going forward, said Meredith Barton, a biologist in the U.S. Fish and Wildlife Service’s Northeast Fisheries Center in Lamar.
Brook trout face increasing challenges, from habitat fragmentation to climate change, she said. The impact on fisheries will play out “over generations.”
If brookies are to survive and thrive, it’s important that they can move and mingle.
“The ability of these brook trout populations to persist and also adapt to these changing habitat and environmental conditions is a function of the underlying genetic diversity of these populations,” Barton said.
