How a School of Herring Makes Noise
Herring can release gas from their swim bladders—the gas-filled organs that help them control buoyancy—through a duct near the anus. As the gas escapes in small bursts, it produces quick, repeated clicks. A single fish makes a faint sound; many fish releasing gas around the same time can create a much larger, sustained underwater noise.
The sound is unusual because it is not the familiar growl or rasp produced by some fish using muscles or vibrating body parts. It is a stream of tiny bubble-like impulses, which can blend together when a school is dense.
Why the Noise Could Sound Like a Submarine
Anti-submarine crews listen through underwater microphones called hydrophones. Their job is to detect and interpret sounds traveling through the water, including the machinery and movement of vessels. But a hydrophone records sound, not its source: the same recording may be interpreted differently depending on its rhythm, pitch, and background conditions.
A large herring school can produce a persistent, patterned rumble that resembles the kind of signal crews are trained to notice. In the conditions of a tense search, the sound could be mistaken for a submarine—or at least treated as a possible clue worth investigating. The resemblance did not mean the fish were imitating a vessel; it arose from many small biological sounds adding up to one misleading acoustic pattern.
The Ocean’s False Alarm
The episode illustrates a basic challenge of underwater listening: a convincing signal is not necessarily a clear identification. Water carries sound over long distances, but it also mixes noises from animals, weather, and human activity. A school of fish can therefore turn an ordinary bodily process into a sound large enough to complicate surveillance—without any fish making a sound that would seem dramatic on its own.
