Researchers recording underwater sounds in the Hudson River thought they were picking up the rumble of passing trains. The noise turned out to be something far older.
The sound came from Atlantic sturgeon spawning on the river bottom. A team of scientists from the New York State Water Resources Institute, Cornell University, the New York State Department of Environmental Conservation, and other partners has confirmed for the first time that Atlantic sturgeon produce a distinctive low-frequency thunder during spawning. The study was published in the journal Endangered Species Research in 2025, according to a report by Phys.org.
"It's almost that you feel it more than you hear it," said Maija Niemistö, science educator with the New York State Water Resources Institute. "You can hear these chirps and squirts and bubbles underwater, but this is a different experience entirely. These are ancient fish, and the thunder — it's almost like you're brought back in time, because they've been making this sound, communicating with each other, for millions of years. It's awe-inspiring."
The discovery came through passive acoustic monitoring, a technique that involves placing hydrophones, which are underwater microphones, in the water and recording over long periods of time without disturbing the animals. The method has been used widely in marine and land-based research but far less often in freshwater environments. The noninvasive approach gives researchers a new tool to find and track sturgeon without handling them.
That matters because the Atlantic sturgeon population has not recovered, even after nearly three decades of legal protection. An estimated 6,000 Atlantic sturgeon once traveled up the Hudson River to spawn during the height of commercial fishing in the late 1800s. Today, fewer than 700 remain. The Hudson River still holds the largest population of Atlantic sturgeon anywhere.
Rebecca Cohen, a postdoctoral researcher at the Cornell Lab of Ornithology's K. Lisa Yang Center for Conservation Bioacoustics and a research lead on the project, put the stakes plainly.
"They've been an integral part of the ecosystem for millions of millions of years," Cohen said. "Trying to support and hold on to this remnant population is the best bet for maintaining the Hudson River ecosystem that functions in the way we all benefit from."
The original study was conducted at a known sturgeon spawning ground. This spring, the team expanded the work, placing additional underwater recorders in areas where spawning is suspected but not yet confirmed. Some of those locations are not currently protected. If the acoustic monitoring picks up the thunder sound there, it could push researchers and regulators to extend protections to new stretches of the river.
The Atlantic sturgeon was decimated by overfishing in the 19th and 20th centuries. Even with protections in place since the 1990s, the species has not rebounded to anything close to its historical numbers. Finding spawning grounds that were previously unknown could be a key step in understanding why recovery has been so slow and what habitat the fish still depend on.
