The following excerpt is from the book The Fisherman’s Ocean by David A. Ross, Ph.D. Reprinted with permission from Stackpole Books, Mechanicsburg, Pennsylvania.
Fish and Sound
Although the study of sounds made by fish is really just beginning, it seems probable that sound-making is a common phenomena among many marine species. Fish can make sounds in a variety of ways, such as by grinding or snapping their teeth, by vibrating their swimbladder, by using their muscles, or by moving parts of their skeleton. Individual fish may also make sounds when courting or mating, or as just part of their normal behavior.
In general, fish are usually very sensitive to and cautious about unfamiliar sounds, even in deep water. For example, sound transmitted into the water through a boat’s hull as a careless angler drops something on the deck may spook any fish in the vicinity. Boat engines or noisy wading can have the same effect. Some anglers put marine carpeting or similar sound-dampening material on their boat decks to reduce noise. Some of the newer flats boats are designed to reduce the thump caused by waves hitting the hull.
Bob Cox, a British fisherman and author of an interesting book entitled Uptide and Boatcasting, feels that casting from a party boat is really the way to fish. By casting he means tossing bait rigged with heavy sinkers. He makes a subtle point about how an anchored boat (30 feet or so in length) in a current can influence where the fish will go. Based on his experience, Cox believes that an anchored boat produces sounds that cause moving fish to divert away from the boat and pass to either side. He writes, “A boat at anchor is like a giant double bass. The hull is the sound box and the anchor rope held tight by the pull of the tide is the string.” He further says that “the rip of the tide and the slapping of the waves against the hull are transmitted down the rope to the seabed along with any noise the anglers on board may make.” He then suggests that you will always do better by casting upcurrent (before the fish are spooked by the boat) or far to the side of the boat, where the spooked fish have moved. It’s not evident if a similar effect could occur with a boat smaller than Cox’s 30-footer. It’s an interesting idea, and although it’s not backed up by any real proof, it seems logical.
Sometimes fish get used to noises, such as boat engines, and show little response to such sounds. Some fishermen feel that a change in the speed of an engine, or starting up an engine, will spook fish. Some offshore anglers believe that game fish such as tuna and sailfish are actually attracted to the noise and vibrations coming from a moving boat. Nevertheless, a cautious angler would do well to keep noise to a minimum.
Scientists have limited data on the ability of fish to discriminate between different sound intensities or sound frequencies. But it seems as if some fish have the ability to analyze the structure of a sound and identify its source, direction, and distance. In doing so, the fish can determine if the sound is coming from a predator or from prey, a piece of information that can be very important in the ocean, where a fish’s vision is limited. Wounded or hooked fish often make a distinctive vibration that quickly attracts predators to the scene. Something about these vibrations, perhaps their frequency or intensity, signals the fish’s distress to others—how else could a predator select just the wounded or injured fish from among the many in a school? Baitfish often detect sounds coming from predators, and by making their own specific sound or alarm they may alert schoolmates of the threat. Fish can also be attracted to the sounds made by other fish chewing and eating. In this way, sound can work for you if you can imitate a baitfish swimming, eating, or in distress, and thus arouse a larger fish’s curiosity.
A few marine animals have the ability to produce and use sound, like sonar, to detect objects in the water, including food. This ability, called echolocation, is very well-developed in porpoises (which are mammals, not fish) and is demonstrated by the high-frequency sound clicks they make. Their ability to locate objects as small as an inch is legendary, and is often a highlight of marine shows. Some fish have similar sound-making ability, but none to my knowledge use it to hunt; rather, the sound is used in various methods of communication, including looking for mates and indicating danger.
In next Wednesday’s Fish Facts Ross explains more about fish SENSES and how to apply them to improve your fish-catch stats.