WHY DO SOME FISH MAKE SOUNDS UNDERWATER?
Chris Kehrer, Science Program Manager at Port Royal Sound Foundation in South Carolina, recently answered a question I have wondered about since childhood. Why does the Atlantic croaker, a marine fish commonly found in sounds and estuaries from Massachusetts to the coast of Texas, sometimes make a croaking sound when pulled into a boat on a hook and line? I also asked some follow-up questions, including why do some croak when caught but others do not? Chris has done some amazing research on sound production in fish and was the right fish biologist for me to pose such questions to.
The first two answers were straightforward. Male croakers are one of many marine fishes that make underwater sounds. Their noise making is especially conspicuous because they continue to croak when pulled from the water. Females do not make sounds, which explains the silent ones. How do fish produce underwater sounds? According to Chris, fish make a variety of sounds in myriad ways. One mechanism used by a family of marine fishes aptly called drums is to inflate the swim bladder and vibrate a specialized muscle thus creating a drumming sound. Red drum, black drum and croakers use this method, which is audible to humans underwater and in the air. Some fish use a sound-producing process that requires the use of so-called pharyngeal teeth located in the throat rather than the mouth. Used in capturing prey and in grinding food before digestion, the teeth produce sound when rubbed against each other. Common sound producers in coastal waters include toadfish, marine catfish and spotted seatrout.
How far do fish sounds travel underwater and how do they vary? Underwater sounds can travel hundreds of miles, depending on the source, which may be important for whales and dolphins. But among smaller fish, such great distances are not as important and sounds are usually more localized. Nonetheless, as with birds, in which sound production is a major component of defining territories and attracting mates, variation is high between fish species and even between individuals. Some fish use different frequencies to avoid noise competition during overlapping mating periods. Others have equally compelling reasons to vary their sound frequencies. For example, silver perch found from New York to Mexico reportedly have evolved a high-frequency sound outside the hearing range of a major predator, bottlenose dolphins.
When someone mentions ocean pollution, we immediately think of serious assaults on all marine wildlife from industrial and agricultural chemicals, urban sewage, garbage and gradually rising ocean temperatures. All these can have negative environmental impacts. For some marine fish, noise pollution can be detrimental as well. One aspect of research on sound production by fishes is understanding how their reliance on sound production is affected by human activities. We make a lot of noise in the ocean, especially in coastal areas where many marine fish live and depend on underwater communication to survive.
Most of us are aware of the importance of sound for survival of creatures around us like birds, frogs and insects. Audio communication is clearly an equally important mechanism for defense and reproduction in many marine fish species. Dedicated scientists are making headway in unraveling the mysteries surrounding the intricacies of timing and interactions within and among these species. Basic questions still need answers, such as what is the full array of fishes that rely on sound production as part of their repertoire of communication? What seasons and times of day do various species make sounds? How do some species change their sound production in response to the presence of predators, prey or interspecies rivals?
Let’s hope that the federal grants needed to support such important research will be forthcoming to provide ecologists with the funding needed to continue their quest to understand the complexities of sound in the ocean environment and how we influence it.
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