This winter, a sudden cold snap led to fish kills around the Chesapeake Bay. Washed up on shores were Atlantic menhaden, and speckled trout. In 2025, a freeze killed young red drum.
Scientists have been studying movements of fish for decades. One team from the National Centers for Coastal Ocean Science is in the middle of a three-year study of two of the Chesapeake Bay’s iconic trophy fish-- red drum and striped bass.
They’re looking at how warming waters, extreme weather and other factors affect the fishes’ movements in and out of the bay.
Brianna Cahill is a marine ecologist working for the National Oceanic and Atmospheric Administration. She’s monitoring a transponding hydrophone, which is an underwater microphone.
"Okay, talking to it. The status it says armed, so that means that it's still locked," Cahill says from the deck of a small boat near the mouth of the bay. "We can go through and activate it."
The hydrophone is talking to an acoustic receiver anchored to the bottom of the bay some 30 feet below that logs data from tagged fish. She’s telling it to come to the surface for retrieval.
"We're 65 meters away, it's opening. So, maybe keep eyes out on the bow," she tells the crew. "Keep eyes out, we'll see two floats and usually a plume of sediment coming off of it. It's at the surface, and we are 92 meters away. Yep, hydrophones up."
The device is about the size of a liter-soda bottle. It’s one of 30 deployed around the bay. They have been collecting data from nearly 250 striped bass and red drum tagged in 2024 and 2025. But tagging is not how it sounds. It’s actually a surgically implanted transmitter about three-quarters the size of a double-A battery.
"We just do a small enough incision to get the tag in and it only needs one stitch to close," says Bethany Williams, a research ecologist with NOAA’s National Centers for Coastal Ocean Science.
Each time a tagged fish passes by an acoustic receiver it pings and transmits data. As part of the Atlantic Cooperative Telemetry Network they receive even more data on their fish through an exchange among other projects using similar receivers their fish might ping. And there are other collaboratives as well.
"So, that's part one, right, tracking the fish and seeing where they go. And then we get all those locations back and we get the temperature data and the depth data that they were recording in their internal tags at all those points," Williams explains. "And then we take each of those points and we overlay them with environmental conditions."
Rapidly warming oceans, ocean acidification, marine heatwaves and extreme weather events are transforming marine ecosystems and potentially the behavior of these fish. This data will help fisheries managers determine how best to keep fish populations healthy and not overfished.
Marine Biologist Laughlin Siceloff holds the retrieved acoustic receiver.
"You can see it's covered in different kinds of fouling organisms. Worms, sea-squirts, sponges, oysters, algae. And here's the receiver itself," he says, "which is actually wrapped in pantyhose."
Yup, you heard it right. This high tech equipment uses low-tech protection from the underwater elements.
"The pantyhose just works really well, the protective and fouling. And I think the acoustic tracking field is keeping the pantyhose industry afloat," Siceloff jokes.
The next acoustic receiver they retrieve doesn’t have the technology to release itself so Laughlin and Brianna will dive into the bay’s chilly waters for it. In six months, they’ll be back for another five days to do it all again.
