. Coast watch. Marine resources; Oceanography; Coastal zone management; Coastal ecology. Illustration by Neil Caudle Scoping the catch as it swims With the flip of a switch, one piece of electronic wizardry—a depth recorder—listens to the sea beneath a fishing boat and shows the captain graphically what it hears: fish. He sees his catch before he ever lowers a net. The depth recorder works like this: a transducer, mounted on the boat's hull, transfers electrical impulses into mechanical sound vibrations that are broadcast at millisecond intervals down into the water in a conical beam. When the
. Coast watch. Marine resources; Oceanography; Coastal zone management; Coastal ecology. Illustration by Neil Caudle Scoping the catch as it swims With the flip of a switch, one piece of electronic wizardry—a depth recorder—listens to the sea beneath a fishing boat and shows the captain graphically what it hears: fish. He sees his catch before he ever lowers a net. The depth recorder works like this: a transducer, mounted on the boat's hull, transfers electrical impulses into mechanical sound vibrations that are broadcast at millisecond intervals down into the water in a conical beam. When the vibrations strike objects in the water, such as fish, the pulses are reflected back toward the surface. The transducer receives the pulses and con- verts them back into electrical signals which are fed into the depth recorder. By calculating the time it takes for sound pulses to reflect back from ob- jects or the ocean floor, the recorder can produce a display on paper or on a color video screen that shows the fisherman a sketchy image of what is beneath him. Depth recorders can determine water depths, record a graphic profile of the ocean floor, indicate the com- position of the bottom and locate fish beneath the boat. Today's commercial and recreational fishermen consider this piece of electronics almost as valuable as their first mate. "You're wasting your time if you fish without a depth recorder," says Ken Kramer, a Morehead City com- mercial fisherman. "If you don't have one, you're putting yourself at a disad- vantage by not being ; Kramer has had his boat equipped with a recorder for ten years. Kramer bottom fishes. He uses his recorder to locate schools of fish and determine the composition of the ocean floor. He looks for areas with a hard bottom made of shell, rock or coral—one that attracts the baitfish on which larger, more valuable fishes feed. Depth recorders are also called echosounders or fish finders. But Kramer says the
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Keywords: ., bookcentury1900, bookcollectionunclibra, booksubjectoceanography
