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Compiling the First-Ever Color Portrait of Narraguagus River Thermal Habitats

May 24, 2024

Celebrating World Fish Migration Day, we check in with Valerie Ouellet, intrepid researcher studying this key habitat for endangered Atlantic salmon.

Brook trout smolt in aquarium. A brook trout fry captured by Ouellet during a study investigating cold-water fish habitat productivity. Credit: NOAA Fisheries/Benjamin Tumolo

Valerie Ouellet has a passion for freshwater ecology. “I grew up fishing salmon and trout in Quebec, Canada, and I am connected to both fish and rivers. For me, trying to find ways to conserve migratory fish species and their critical habitats is really a passion. I have two little boys. I want them to be able to have those connections to aquatic ecosystems. Without those habitats, that won’t happen.”

This summer, Ouellet hopes to take a big step forward in her work. She’s launching a pilot project using specialized infrared camera equipment and a helicopter to map surface temperatures along an entire river system in Maine. The river provides habitat for endangered Atlantic salmon and other migratory fish. If it goes well, the next step is to expand this kind of monitoring to more rivers and build local capacity in Maine to achieve it.

The mapping project is a collaboration between our Atlantic Salmon Ecology Research Branch and the U.S. Department of Agriculture’s Natural Resources Conservation Service. “I designed this pilot project so we can have a blueprint for how to use the information in partnership with the Natural Resources Conservation Service, while supporting a parallel effort with many partners to replicate this work across Maine,” said Ouellet. Partners include state and federal agencies, the Penobscot Nation, environmental non-profit organizations, and universities.

“This important collaborative work is funded under President Biden’s Inflation Reduction Act—the largest climate investment in American history and part of the Investing in America agenda,” said Matt Walker. Walker is the Maine state conservationist for the Natural Resources Conservation Service. “Working in partnership with the science experts at NOAA, our goal is to help identify more opportunities to support the critical Atlantic salmon habitat.”

All the Connections We Cannot “See”

Sea-run fish connect ecosystems throughout their life cycles. Ouellet’s work is about restoring connectivity where it has been disrupted, to improve conditions for migratory fish populations. Dams are an obvious example of a disruption, because they are a barrier to fish migration. Ouellet is looking at something that’s equally important but harder to see.

A color image taken underwater showing multiple sea run fish species making their way upstream.
Milford dam fish passage on the Penobscot River (Maine) showing Atlantic salmon and river herrings. Credit: Penobscot River Restoration Trust/Cheryl Daigle A color image taken underwater showing multiple sea run fish species making their way upstream.

“A dam is a big physical barrier that prevents fish from moving,” she explains, “but there is also connectivity we don’t see. Rivers are getting warmer and as that happens, stretches of a river can get so warm that they affect connectivity just like a dam does! We have a lot of species that only migrate a short distance up our rivers but Atlantic salmon, sea lamprey, and American eels have crazy long migrations. They are more affected by loss of connectivity. The cold water patches I study are particularly essential to them, especially salmon.”

Rivers contain a patchwork of depths, water velocities, and flow, and temperatures that change over the seasons creating a variety of habitats. Species move in and out of these to find the optimal places to grow, eat, digest their food, rest, and breed. Fish use both warm- and cold-water habitats during their life times, but as rivers warm there is concern that cold-water patches will become scarcer or weaker. “We are trying to improve the habitat by doing restoration,” she said. “With this baseline map we can target our efforts where they will be the most effective.”

Mapping Temperature in the Narraguagus

River with quick flow, some white water, trees along shore line and bridge in the background.
A stretch of the Narraguagus River in Maine. Credit: NOAA Fisheries/Valerie Ouellet

The Narraguagus River is one of seven in Maine that supports the nation’s only remaining wild populations of Atlantic salmon and is the site of the pilot project. Ouellet and her team will take the thermal images this summer and then analyze how the different thermal habitats are arranged at the riverscape scale. With that information, researchers can better understand:

  • What cold water habitats are key to species resilience
  • Where to direct our restoration efforts
  • Where the river is most likely to have better productivity

Infrared thermal imaging allows us to see what the human eye can’t detect, capturing a color-coded image of the river reflecting temperatures of the water and adjacent land. “You can also do that with a drone, but you only get short stretches of the river. With a helicopter you can map the whole system. I am working with colleagues from the United Kingdom, France, Canada and the United States to share expertise and bring us up to speed on these technologies.”

Both drone-based imaging and larger scale imaging have value, but a baseline map would provide the first ever comprehensive look at the river as a whole. Ouellet noted the importance of the consistent monitoring that is already taking place. “A map is a snapshot in time. Routine, place-based monitoring provides a measure of change over time in a variety of factors.”

A Conservation Legacy

Net with alewife on rocky shore, as seen from above, with a child in red boots and scarf.
Ouellet and her son netting alewife at the Blackman Stream in Bradley, Maine for a talk about fish migration. Credit: NOAA Fisheries/Valerie Ouellet

Ouellet believes that this work can substantially improve prospects for restoring rivers and migratory fish, and the watershed as a whole. This could inform all kinds of conservation decisions. 

“You look at the surface of the river and you don’t usually see fish, at least not a lot—but suddenly in the spring the river is moving, black with fish, and this is just a small portion of what our ancestors saw. This is a legacy that I hope we can preserve for future generations so they will keep seeing that and enjoying that moment.”

“By developing tools and products for climate mitigation and resilience, this can ultimately enhance coldwater fish resources beneficial to both recreational and at-risk species,” said Walker. “The Natural Resources Conservation Service is committed to being part of cooperative partnerships like this that address natural resource concerns through scientific and cooperative avenues.”

Last updated by Northeast Fisheries Science Center on May 24, 2024