When we imagine the ocean, a tranquil blue underwater world may come to mind. But the deep sea is filled with an incredible variety of sounds. From grunts and splashes to sharp whistles, many of these sounds come from the communication behaviors of marine life, used to send signals to each other. Herring, for example, uses “farts” to transmit messages, helping schools maintain formation or avoid predators.
Herring is not only a vital food source for marine predators like whales, seals, and dolphins, but also an everyday staple in human food culture. For most of us, herring is associated with processed, canned fish, with a strong, yet delicious flavor.
In the BBC documentary Ocean Spy, a robotic herring with a camera successfully integrated into a giant shoal of thousands of herring swarming to lay eggs. The spy fish captured the scene and sounds as the herring expelled air from their swim bladders, creating a farting sound unique to them.
The sound of a fart almost started a war
The seemingly innocent herring farting noises started a misunderstanding that nearly led to a national security incident between Sweden and the Soviet Union (USSR) during the Cold War era (1947-1991).
In 1981, a Soviet submarine ran aground off the southern coast of Sweden, just 10 kilometers from a Swedish naval base. Although the Soviet Union claimed it was accidentally forced into Swedish territorial waters due to a navigation error, Sweden believed it was a deliberate attempt to infiltrate Swedish waters. Consequently, the government maintained a high level of alert in its waters.
Shortly afterward, the Swedish Navy recorded a mysterious underwater sound during routine monitoring. These strange noises were not unique. The sound, remarkably like that of a submarine propeller, led the military to strongly suspect a Soviet submarine had once again entered Swedish territorial waters. Submarines and ships were immediately dispatched to conduct a thorough search. Due to the heightened Cold War tensions at the time, Sweden even prepared to enter a state of combat readiness.
Even as late as 1996, the Swedish Navy continued to detect the same noise. Each time the sound was heard, a large-scale search was launched, but the results were always fruitless, save for the occasional sighting of bubbles on the sea surface. The increasingly suspicious Swedish government even protested to Russian Prime Minister Eugene Yelchin, accusing Russia of continuing its post-Cold War provocations. Relations between Sweden and Russia subsequently became strained.
The truth wasn’t revealed until Magnus Wahlberg, a marine acoustics expert at the University of Southern Denmark, was invited to investigate, and a plausible explanation for the underwater noise that had long troubled the Swedish military was finally found. Comparisons and experiments confirmed that the noise was not coming from a submarine, but rather a “collective bubbling” sound caused by a large school of herring simultaneously releasing air.
Scientific analysis revealed that herring have swim bladders connected to their digestive systems and can expel a series of tiny bubbles through their anus. When a school of herring is stressed or startled, these bubbles are released rapidly, producing a distinctive sound. This sound is called FRT (Fast Repetitive Tick). When a large school of herring gathers, the entire water area resonates with a repetitive “bubbling” sound. This not only helps the school maintain formation in dark or chaotic environments, but also allows them to quickly turn when startled, alerting their companions to escape predators.
In other words, the mysterious noise mistakenly attributed to submarine propellers during the Cold War was actually a natural phenomenon caused by the unique physiology of herring and their swarming behavior. To verify this, Magnus Wallberg bought herring from a store and simulated pressure on the fish in an experiment. Sure enough, the herring produced the same bubbling sound. When he played the recording to Swedish naval personnel, they were stunned. It was the same noise they had been vigilantly monitoring for years.
The story finally came to a close: The enemy submarines the Swedish military had been searching for and mobilizing troops to track down for over a decade were actually just the noise of thousands of herring farting simultaneously.
Translated by Patty Zhang and edited by Helen London
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