It is also used in
fishing methods in which the fisherman searches for tuna at a distance, grasps
the movements of the tuna, and then goes around in front of the fish to catch
them by flushing bait before their noses, such as fishing of tuna in Oma,
Aomori Prefecture, which is often broadcast on TV.
On the sonar
screen, the center of the screen is the position of own ship. Also, ultrasonic
waves are transmitted into the sea at the time the screen is updated. The range
is a radius way centered on the ship, and the range is 2,000 meters for
long-range sonar, or even longer. Compared to echosounders, sonar has a wider
detection range in the ocean and can transmit sound almost horizontally, making
it possible to detect fish schools swimming relatively close to the surface. It
is also possible to determine whether fish flee when a ship approaches (escape
behavior of fish schools).
However, this is difficult to quantify, and
resource surveys using sonar is less developed, so the realization of it is
needed immediately. If we can do it, the detection range will be expanded, and
we will be able to grasp the state of resources in a wider area of the ocean in
a shorter period of time. Our laboratory is also making efforts in this area.
【Card description】
While echosounders search almost directly under the ship, sonar can search in front of the ship and to the side. Therefore, it can search for fish schools far away from the ship. Sonar is often used in the purse seining, where a net is cast around the fish school while predicting the movement of the fish school. It is also used on the tuna fishing boats in Oma, Aomori Prefecture, which are often shown on TV. The boats search for tuna in the distance, know the movements of the fish, and go around in front of the fish to catch them by flushing bait down the fish's nose. Incidentally, SONAR is an acronym for SOund NAvigation and Ranging.
