State College, Pa. — You’ve heard about movers and shakers. How about movers and stayers?
Those are wild Pennsylvania brook trout.
Some are more cautious than others, tending to remain in their home waters forever. Others are more adventurous and, every now and again, wander far afield before returning home.
Researchers at Penn State determined that by putting microchips in fish in several watersheds and monitoring their movement.
Tyler Wagner, assistant leader of the university’s Cooperative Fish and Wildlife Research Unit, said students followed wild brookies for several years. The goals were several.
That information helps biologists understand how fish respond to habitat and food, deal with changing water temperatures and even seek to reproduce. For anglers, Wagner said, it can inform them about where to fish and when.
And for fisheries managers, it can inform stocking decisions.
What they found, in all cases, are that fish – like people – are individuals.
“There’s a high variability among fish. Some are movers and some are stayers,” Wagner said.
“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.”
It’s important that both kinds of fish are out there, said Meredith Barton, a biologist in the U.S. Fish and Wildlife Service’s Northeast Fisheries Center in Lamar.
Brook trout face a lot of challenges these days, she said. There’s habitat fragmentation and degradation, climate change and more. Their impact on fisheries will play out “over generations,” she added.
It’s vital that fish populations – movers and stayers mixing together – can intermingle.
“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.
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.
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.
That highlights the importance of what he called “connectivity” between waters.
“These warm streams, in a lot of cases, are providing that dispersal corridor,” he said.
By studying movement – and using genetic testing to see which populations are getting movers and which aren’t – fisheries managers can maintain those corridors, Barton said. They can do that by identifying barriers to movement and perhaps eliminating them, she added.
Populations need both movers and stayers, Wagner added.
“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 and brown trout,” he said.