Fish Detection

Fish Detection

Fish detection refers to the actual position of a fish school. It is a matter of communication between fish and man, or fish and some device/ equipment in a water body. The position of fish is first detected and then net or other fishing gear is used to catch those fish from different water depth.

Methods of detecting the fish school

After assumption about the location of fish school, one can detect them following ways:

1. Sampling
2. Aerial scouting
3. The use of instrument

                    a)    Sampling:

Detection of fish or fishing ground can be performed by using gill nets, trawl nets, long lines etc.

           b)  Aerial scouting

• Use of a powerful  camera from aeroplane
• Fish school sighted –in evening and morning
• For Iceland, optimum flying height 800 ft
• Can  detect from a distance of up to 10 miles
• Pilot or skipper give direction and guidance to the fishing vessels
• Deep sea large water bodies can be surveyed within short time

  

              c) Use of instrument

Most instruments used are:

1. Echo ranger
2. Echo sounder
3. SONAR

1) Detection by echo-ranger

With the help of eco-ranger fish can be detected horizontally which extends up to two miles from the ship. Here the sound beam travels horizontally. It is specially used for detecting pelagic or mid-water fish.

2) Fish finder/ echo-sounder

An echo-sounder or fish finder is used to measure

                                                I.     The depth of water

                                              II.     Bottom topography

                                            III.     Fish shoals/ schools at different  depth of water

This instrument is designed to radiate sound wave of known frequency vertically through a transducer (set at the bottom of fishing vessel) in water down to get the reflections echo from the bottom or fish shoals or some other objects in front of the transmitted wave. This wave again is received by the transducer which is send back to a recorder and the return time is processed electronically and recorded on paper or displayed on CRT (cathode Ray Tube).

3) SONAR (Sound Navigation and Ranging)

SONAR includes all underwater acoustic systems used for the detection of the underwater objects, though recently the term Sonar has been used for an echo-sounder for horizontal detection in a narrow sense. The Sonar records or displays the reflected wave from an object under the water on recoding paper or a cathode Ray Tube (CRT) by scanning the transducer horizontally. Recently most Sonar have been designed for either horizontal or vertical or both (by using large beam wave) use.