Herring Break Wind to Communicate, Study Suggests
James Owen in England
for National Geographic News
|November 10, 2003|
In polite society, flatulence is often a social faux pasespecially when issued deliberately. But in the world of fish, group "raspberry-blowing" sessions appear to perform an important social role.
This intriguing idea comes from scientists who discovered that herring create a mysterious underwater noise by farting. Researchers suspect herring hear the bubbles as they're expelled, helping the fish form protective shoals at night. It's the first ever study to suggest fish communicate by breaking wind.
The study's findings, now published online in the U.K. science journal Biology Letters, reveal that Atlantic and Pacific herring create high-frequency sounds by releasing air from their anuses.
"We know [herring] have excellent hearing but little about what they actually use it for," said research team leader Ben Wilson, a marine biologist at the Bamfield Marine Science Centre, British Columbia, Canada. "It turns out that herring make unusual farting sounds at night."
Wilson and his colleagues named the phenomenon Fast Repetitive Tick, which makes for the rather mischievous acronym, FRT. But unlike the human version, these FRTs are thought to bring the fish closer together.
Two teams carried out the research in Canada and Britain. One team studied Pacific herring in Bamfield, British Columbia, while the other focused on Atlantic herring in Oban, Scotland. The fish were caught locally and transferred to large laboratory tanks where their behavior was monitored using hydrophones and infrared video cameras.
The fish were found to produce high-frequency sound bursts up to 22 kilohertz. The noise was always accompanied by a fine stream of bubbles.
"In video pictures we can see the bubbles coming out of the anal duct at the same time," said Robert Batty, senior research scientist at the Scottish Association for Marine Science in Oban. "It sounds very much like someone blowing a high-pitched raspberry."
Further tests revealed these outbreaks of "flatulence" are not a response to fear or feeding. When high concentrations of shark scent were introduced to the tanks, there was no noticeable increase in bubbles or sound. Similarly, unfed herring maintained the same level of emissions.
"The evidence suggests it's not gut gas that's responsible," Batty said. "If you starve the fish, they still produce this sound." Instead of gas, he says the fish use air gulped from the surface which is then stored in their swim bladders and expelled through a duct with an opening next to the anus.
What seems to trigger the noise is darkness and high fish densities, suggesting that herring use farting as a means of communication.
"Herring and other clupeids such as pilchards and sardines have a sophisticated auditory system," said Batty. "This is made even more sensitive by a gas-filled sac near the inner ear which acts to amplify sound pressure."
Clupeid fish, like herring, anchovies, and sprats, can detect sound frequencies up to around 40 kilohertz, way beyond the hearing range of most other fish. (The normal range of human hearing is 20 to 20,000 kilohertz.) So a method of nighttime communication using pulses of air would be extremely useful. It would enable herring to maintain contact after dark, but without giving their position away to predatory fish.
While unusual, other marine fish are known to communicate using sound. For instance, male cod make a noise to attract females when they breed. But Batty adds: "These are produced using the swim bladder, which vibrates to create a kind of drumming sound. However, the method we found hasn't been noticed before."
The researchers say further studies into how herring produce such sounds could help fishermen in locating shoals. Pacific and Atlantic herring are both important commercial species in the Northern Hemisphere.
Furthermore, given the herring's sensitivity to underwater sounds, and the likelihood they use them to communicate, there are concerns about the possible impacts of noise pollution. For example, engine noise from shipping or seismic guns used for oil surveys could all interfere with the fish's hearing.
Similarly, herring-eating dolphins and whales, which can pick up high frequency sounds, may use FRTs as a foraging clue. Consequently, noise pollution may seriously impair their effectiveness as hunters, researchers say.
"There are pods of killer whales that specialize in feeding on herring," Batty said. "The fear is they won't be able to pick up the sounds the herring are making."
It might seem an amusing idea to us that herring communicate using farts. But for herring and the mammals that prey on them, FRTs may signal safetyor the next meal.
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