Anchor up in Pamlico Sound on a quiet fall evening, cut the engine, and listen. On the right night, especially in September and October, you might hear something strange radiating through the hull of your boat—a low, rhythmic thrumming that seems to rise from somewhere deep and close all at once. What you’re hearing is red drum, doing exactly what they’ve been doing for tens of millions of years: talking.
Red drum, spotted seatrout, croakers, weakfish, and the rest of the Sciaenidae family are among the most acoustically active fish on the planet. Specialized sonic muscles attach directly to the swim bladder—the gas-filled organ that controls buoyancy—and when a drum wants to be heard, those muscles contract at extraordinary speed, making the swim bladder vibrate like the skin of, well, a drum. The result is a low-frequency pulse that carries hundreds of meters through shallow water.
Each species in the family has its own acoustic fingerprint. Red drum produce a series of deep, repeated pulses that resonate across the estuary. Spotted seatrout have a more complex, staccato-style call. Black drum are unusual in that both sexes call, not just the males. Experienced researchers and a few longtime anglers can tell each species apart by ear alone.
Sound isn’t just a novelty for these fish; it’s central to reproduction. Males are the primary callers, and their drumming intensifies during spawning season, peaking around dusk as water temperatures and lunar cycles align. It’s a biological advertisement, a way of announcing fitness and location to potential mates in waters where visibility may extend only inches. Those evening choruses aren’t random noise; they are the sound of a new generation beginning.
Not all sciaenids rely solely on the swim bladder. Some use stridulation, rubbing together bony structures like teeth or fin spines to produce clicks, rasps, and grunts. The ocean has never been the silent world we once imagined. Fish have been communicating acoustically for at least 155 million years.
Tuned in: Decoding the Deep
If a red drum chorus carries hundreds of meters through Pamlico Sound, imagine what a hydrophone can pick up. Scientists have been doing exactly that for decades, and the results have fundamentally changed how North Carolina manages some of its most prized coastal fisheries.
Pioneering research out of East Carolina University showed that passive acoustic monitoring—deploying underwater microphones at strategic locations and recording whatever the water has to say—could map spawning activity across entire estuaries. Using sonobuoys and hydrophones throughout Pamlico Sound, ECU researchers identified precisely where and when each sciaenid species was spawning. The findings were specific: weakfish and silver perch called predominantly near inlet locations in May and June; spotted seatrout peaked in July at river mouth sites in western Pamlico Sound; red drum choruses built near coastal inlets in September and October. Each species had its own acoustic calendar and its own preferred address.
NC State University’s Center for Marine Sciences and Technology has expanded on this work, using soundscape analysis to link fish sound production with habitat quality, particularly on oyster reefs and surrounding waters. The connection matters: healthy, acoustically rich habitats tend to support more robust spawning activity. Where the drums go quiet, something may be wrong.
What makes passive acoustics such a powerful tool is its reach and patience. A hydrophone doesn’t need a boat crew or a favorable weather window. It doesn’t disturb the fish or alter the habitat. It simply listens, and what it hears can directly inform where fishing regulations and habitat protections are most urgently needed. Spawning habitat is the linchpin of any fish population’s future. Protect it at the right time and place, and you protect the fishery itself.
Meet the Band
The next time you cut the engine and drift, take a moment to listen. What sounds like silence is anything but. Somewhere beneath you, a red drum might be making its case to a nearby female. That’s not just remarkable biology, it’s a measurable signal that turns a drumbeat into a tool for smarter fisheries management.
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