Most animals do not pass gas for any purpose other than necessity. In the oceans, however, there is an animal that may use flatulence as a means of communication.
In the animal kingdom, flatulence is a common byproduct of the digestive process. Most animals do not pass gas for any purpose other than necessity. In the oceans, however, there is an animal that may use flatulence as a means of communication. The technical term for these bursts of sound is Fast Repetitive Tick, or FRT.
Scientists noticed that two fish, the Atlantic herring and the Pacific herring, emit FRTs, high-pitched click-like noises. This happens especially at night, when these fish form schools near the sea surface. By using infrared cameras and underwater microphones called hydrophones, scientists determined that herring were producing these sounds at the very moment that bubbles emerged from their anuses.
In 2003, a team led by Ben Wilson, a biologist at the University of British Columbia in Vancouver, Canada, conducted experiments aimed at figuring out how and why the Pacific herring passes gas. At the same time, Robert Batty and his team at the Dunstaffnage Marine Laboratory in Scotland studied the Atlantic species. The teams caught herring in the wild and transported them to tanks in their labs. They monitored the herring under different experimental conditions, such as night versus day and variations in the amount of food they were fed. Results showed that both species produced very similar bursts of sound.
FRTs per herring were more frequent at night and with other herring around. Herring first get gas by gulping air at the surface, and they release it from their swim bladder through a duct that ends near the anus. This means that FRTs are not a product of digestion. Wilson and Batty hypothesized that herring use FRTs to signal their location, thereby making it easier to form schools in the dark of night.
FRTs have a sound frequency that cannot be heard by large predatory fish such as sharks. But they can be heard by marine mammals, such as dolphins, toothed whales, and seals, all of which depend on herring as a food source. This could mean that while the herring benefit from being able to stick together in schools at night, they may also be announcing their presence to some of the very animals they need to avoid. However, recent observations of killer whales hunting herring suggest that the bubbles produced by herring FRTs may work to confuse the predators and make it more difficult for them to attack the small fish.
Herring are very important to commercial fisheries. For example, more than 115,000 metric tons of Atlantic and Pacific herring were landed in the U.S. in 2004, at a market value of over $30 million. Humans eat herring, but also use it as bait to catch cod, haddock, tuna, lobster, and many other marine species. Scientists and fishermen would like to see if they could use hydrophones or other devices to find schools of herring by listening for their FRTs. Fisheries managers wonder if they could better estimate the size of herring stocks by determining a correlation between the noise of a school of herring and the number of herring it represents. Other scientists are studying whether human-made noises in the oceans military sonar, boat engines, oil platforms, and more are affecting herring, whales, dolphins, and other marine animals that rely on sound.
While the BioZine is on summer vacation, enjoy this article from the archives. It was originally published in May 2008.