Something strange is happening in the brackish waters of New York’s Hudson River. It sounds like a sort of low thundering, and while anything is possible in a lively body of water so closely associated with the Big Apple, it’s not the Teenage Mutant Ninja Turtles training with their rat sensei S plinter. Instead, scientists say that the mysterious sound is made by the reproductive antics of an endangered fish called Atlantic sturgeon (Acipenser oxyrinchus). Writing in a recent Endangered Species Research paper, the team is the first to verify the Atlantic sturgeon’s thundering. The noise is probably caused by males thrashing—and their swim bladders’ resonance—as they fertilize eggs, according to researchers.  “It’s almost that you feel it more than you hear it,” Maija Niemistö, a researcher from the New York State Water Resources Institute and co-author of the study, said in a press release. “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.” They are also classified as Endangered. In the spring, these giants leave the ocean to swim up the Hudson River to spawn. For sturgeon, this reproductive behavior involves males and females releasing their necessary parts into the water. In other words, the egg doesn’t fertilize inside of the female fish.  The team eavesdropped on the crucial life cycle process with passive acoustic monitoring. They recorded sound within the waters of the Hudson River with underwater microphones for long periods of time. Though this noninvasive strategy is a common approach in marine and terrestrial research, it hasn’t been used as much in rivers and lakes with more freshwater.  Now, the team’s discovery of sturgeon thundering provides the New York State Department of Environmental Conservation (NYSDEC) with an additional way to help monitor and better understand  Atlantic sturgeon behavior. As we frequently report, the more researchers know about a species, the more equipped they are to protect it.  And the Atlantic surgeon certainly needs it. In the 19th and 20th century, overfishing greatly decreased their populations. Unfortunately, almost 30 years of protection hasn’t helped the species make a comeback. Part of the problem is that female Atlantic sturgeons can wait up to two decades before their first spawn. “That’s why they’re so susceptible to overfishing,” added Amanda Higgs, also co-author of the study and a fisheries biologist with NYSDEC Hudson River Fisheries Unit.  Eggs could represent 20 percent of a female’s substantial weight and fisheries were interested in their caviar. “A female was a lucrative catch,” Higgs added, “and so they got wiped out relatively quickly because they don’t have the ability to reproduce and replace themselves quickly.”  While experts estimate that 6,000 Atlantic sturgeon spawned in its waters before the late 1800s, today less than 700 spawn here. Nonetheless, the Hudson River is home to the species’ largest population.  Moving forward, the team can listen for previously unknown spawning grounds, enabling the state to deal out protections for these endangered river giants.  The post Sturgeon sex creates thundering noise in New York appeared first on Popular Science. ...read more read less