Fish-Finding

Fish-Finding

 

a method of locating (for commercial purposes) and studying the behavior of fish, marine mammals, and other aquatic organisms by means of active and passive underwater sonar detection. Fish-finding systems generally are of an active type that can determine the species, size, and number of fish, as well as the position of the schools.

The basic difference between fish-finding and underwater sonar detection (hydrolocation) lies in the sound reflection and scattering characteristics of aquatic organisms. Since the acoustic properties of fish tissues and seawater are similar, the scattering and absorption characteristics are determined mainly by the swim bladder. There is a very substantial difference between the acoustic impedances of water and of the gas within the bladder. According to calculations, the swim bladder should reflect approximately 50 times more sound energy than the body. However, measurements show that this energy is two to five times less. The apparatus used in fish-finding includes both underwater sonar detectors and echometers.

The effectiveness of fish-finding can be reduced by the presence of scattering layers that are created, for example, by plank-tonic organisms. The layers may also be created by reverberation (surface, bottom, and volume), which is often difficult to distinguish from the reflections of schools; by temperature non-uniformities (horizontal and vertical), which register like scattering layers; by wake echoes that are frequently encountered when a large number of vessels are operating in an area, and by interference from beams emitted by sonar detectors and echometers on various vessels.

REFERENCES

See references under BIOHYDROACOUSTICS.

V. M. LIFSHITS

References in periodicals archive ?
Last Thursday, the Vice President went to Ilin Island in San Jose, Occidental Mindoro to give 12 units of global positioning system and fish-finding equipment from Angat Buhay partner Marnav Marine Electronics to the crew of sunken fishing boat Gem-ver.
Raymarine and Navionics have partnered to make several new features available on Raymarine's LightHouse II based multifunction displays (MFDs) that will make navigation, fish-finding and exploration safer and easier for boaters.
Both boats are licensed and insured and carry full fish-finding and safety equipment.
Fish-finding mobile app BassForecast is now available in the App Store, the company said.
We intend, on calm days, with the aid of the on-board 'fish-finding' technology to catch our supper.
The first three sessions taught about equipment, fishing strategies, ice safety, reading of fish-finding equipment, use of tie-up devices and equipping all-terrain vehicles for fishing.
As an experienced deckhand you could work as a 'mate', with extra responsibilities, such as reading charts and navigating, operating the radio, using electronic fish-finding equipment and deputising for the vessel's skipper.
OAWRS allows the team to take images of an area some 100 kilometers (approximately 62 miles) in diameter every 75 seconds, which is a vast improvement over conventional techniques such as fish-finding echo-sounders.
They systematically overview all major aspects of applying acoustic equipment in commercial fish reconnaissance, and analyze the possibilities of fish-finding techniques.
The Magnuson Act also provided low-interest government loans and fuel subsidies to the fishing industry to expand the fleet, encouraging the industry to take out loans to expand its catching capacity through new technologies like satellite-search systems and deep-scan fish-finding sonar.
They received a global positioning system device, fish-finding equipment, and cash assistance from an Angat Buhay partner and other donors upon Robredo's visit.
Both boats fully licensed and insured and carry all safety and fish-finding equipment.