AUSABLE WATER WISE: Finding the fish

Ausable River Association staff scientists Carrie Pershyn, Liz Metzger, and intern Cat Wang hiked over 80 miles of streams in the region to filter stream water as they looked for evidence of brook trout using a cutting-edge DNA technique called environmental DNA, or eDNA. Their filters capture free-flowing genetic information released into the water by a fish’s bodily fluids or shed skin cells. The research gives the Ausable River Association clues to whether and where brook trout will survive warming water temperatures across the watershed. (Provided photo — AsRA)

Was a little mountain brook trout the first fish you caught? Do you have pictures with older relatives holding stringers of trout from the pond at camp, and big smiles on your faces?

Maybe you don’t fish but you enjoy watching little black darts shoot across the pools of streams you cross while hiking in the High Peaks. These fish are here because of our cold mountain streams with their deep winter snowpacks and our extensive land protection measures.

Brook trout moved back into the Adirondacks as the glaciers left and now live in beaver ponds, lakes, streams, and rivers across the region. These fish have been in the Northeast for several million years, but they could disappear from our waters if we deprive them of the cold temperatures they need to thrive.

Across the Northeast, increasing water temperatures and altered stream flows will lead to shifts in the ranges of fish species. It’s difficult to know where and when these shifts will take place, but we do know there are ways to help fish in the meantime and into the future. The two most important steps we can take for brook trout are connecting separated populations and conserving a variety of habitats for them. To keep brook trout in the Adirondacks, it’s essential that we understand where they are now.

At the Ausable River Association, we have been working on several projects to help conserve and understand brook trout habitat. We visit 30 stream sites across the watershed every other week throughout the year to monitor water quality. We maintain a network of 25 data loggers in the river and its tributary streams that track water temperature once per hour, year-round. We reconnect fragmented stream habitats by replacing culverts where they are undersized. Every spring and fall, we plant trees in riparian areas to increase stream shading and reduce water temperatures. To guide these efforts to help trout, we needed a reliable way of knowing where they are. We have been using a cutting-edge research tool that allows us to capture evidence of fish presence without even seeing the fish. This technique is called environmental DNA, or eDNA for short. It captures free-flowing genetic information that is released into the water by a fish’s bodily fluids or shed skin cells. We filter the water then send it off to a lab, where they do a PCR test (also used for Covid tests) to determine whether the fish species we’re interested in are present or not. Over the past several years, my colleague Liz Metzger and I have hiked all over the Ausable River watershed filtering water to learn where trout are living. Looking for environmental DNA is less time consuming and expensive than traditional sampling techniques and allows us to cover more ground with our small team of scientists and summer interns.

We’re interested in knowing whether brook trout will survive warming water temperatures in different stream types across the watershed. Our research over the past six years has given us a pretty good understanding of how far brook trout populations extend into wilderness areas and private lands. Over the past two years, we’ve hiked, paddled, and waded over 80 miles of streams sampling water in our search for eDNA indicative of brook, brown, and rainbow trout. Out of 150 samples, we found brook trout DNA at 130 sites. We’ve learned that some streams have DNA from brook trout with overlapping populations of brown or rainbow trout. Some streams with small waterfalls or beaver dam complexes had brook trout DNA only for miles. The East and West Branches of the Ausable River are stocked with brown or rainbow trout, nevertheless we found evidence of brook trout living in both branches.

We are already using this information to understand where to spend our energy looking more carefully at trout populations, choosing where to plant trees, and where to recommend that our nonprofit partners focus their land conservation efforts. If you live on a stream and are interested in learning what you can do to help brook trout survive here, contact us through our website to learn more: https://www.ausableriver.org/contact-us.

(Carrie Pershyn is the biodiversity research manager at the Ausable River Association.)

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