섹션 개요

  • Since a sound wave spreads as it goes farther, it can search for a wider range as the distance increases. In contrast, the search range is narrow when the distance is short. Therefore, in the observations with a fish finder, the search range is narrow at a shallow depth (surface layer), and a school of fish cannot be observed at a depth shallower than the bottom of the ship. Sardines, mackerels, and saury, which can be found in supermarkets, are mainly distributed in the surface layer, for which fish finders are suitable. Therefore, sonar is used to find such fish efficiently.

    Sonar is a device that detects fish echoes like a fish finder, but it can transmit sound waves in a horizontal direction (Figure 4). Moreover, because the sound waves can be transmitted all around the ship, it can search a wider range than a fish finder. If a school of fish is captured by a sonar continuously, its movement can be visualized three-dimensionally. The figure shows an example of a certain angle of depression (angle looking down), which be changed to correspond to various schools of fish.

     Please check this. Should it be “unsuitable” as a fish finder only has a narrow range at shallow depths?




    Sonar is also installed on the Oma tuna fishing boat, which may be seen on TV. To catch tuna, fishermen drop bait in front of the school of tuna ahead of time by knowing its movement using sonar.

    Because saury catches have been poor in recent years, the survey of its abundance is important. Since sonars are more suitable for searching for saury than fish finders, the estimation of amount of saury resources using sonars has attracted attention.