Tuning In to the Hidden (and Noisy) Lives of Fish

What if understanding river fish meant listening rather than looking? That question sparked a multi-year research project at the Hudson River Reserve, where scientists and educators set out to uncover the river’s underwater soundscape. 

“The Hudson River is incredibly turbid,” explains Reserve Science Educator Maija Niemisto, “so we decided to listen to what was happening underwater.” 

Using passive acoustic monitoring (essentially underwater microphones), the Reserve-led team gained new insight into fish behavior with implications for recreational fishers, managers, and fisheries scientists.

“Fish actually make a lot of noise underwater,” laughs Chris Bowser, the Reserve’s education coordinator. “Most people imagine them as completely silent, but they’re actually much closer to frogs.”

With funding from the NERRS Science Collaborative, the project set out to better understand the behavior and spatial distribution of fish species in the Hudson River, including endangered species such as Atlantic sturgeon. The team deployed acoustic recorders at multiple monitoring locations, including sites within the Reserve. These devices continuously captured underwater sound, creating a vast dataset that scientists could analyze to distinguish biological sounds from human-made noise like boat traffic.

In the process, the project led to a growing understanding of the river’s fisheries and its ecology. As it does for many research projects, the Reserve supported critical logistics, for example, providing access to boats, storage space, and facilities that made it easier for the team to deploy and retrieve monitoring equipment. The effort complemented ongoing Reserve monitoring, allowing scientists to compare their acoustic data with other observations of weather and water quality data from the Reserve’s System-Wide Monitoring Program.

Education and outreach was also a major focus of the project, which leveraged the Norrie Point Environmental Center, where thousands of students and visitors come each year to learn about the River’s ecosystems. Niemisto and her team created an interactive story map that allows users to “dive into” the Hudson, listen to the underwater soundscapes, and surface again to see the surrounding landscape. Along the way, users interact with photos, sound clips, videos, and quizzes.

“By gamifying the experience of exploring the river via the story map, we bring it to life,” explains Niemisto. “You can explore the acoustics of the Hudson River and click through different sites to learn more about them just like you would in a video game.” 

Bioacoustics is a non-invasive way to monitor species, allowing scientists to observe species without capturing or disturbing them. This is especially valuable when studying endangered fish like Atlantic sturgeon. 

“This project is providing a lot of new information about how to use bioacoustic technology in freshwater and estuarine environments,” says Bowser. “This knowledge is definitely transferable to other Reserves that are interested in non-invasive monitoring and in researching their local sturgeon populations.” 

The project team collaborated with partners at United States Military Academy West Point, the Cornell Lab of Ornithology, and the K. Lisa Yang Center for Conservation Bioacoustics, while also drawing on fisheries data from the New York State Department of Environmental Conservation. Special credit goes to Rebecca Cohen, whose leadership and vision were central to making the research and outreach efforts a success.