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Alaska Fisheries Sonar

Alaska Fisheries Sonar
Sonar Technology Tools

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ADF&G uses DIDSON to record ultrasound-like fish video. DIDSON can also be used to size fish and ADF&G biologists have been testing methods of using it to identify salmon by tail beat patterns.

Alaska Department of Fish and Game sonar tools

Alaska has been a pioneer in the use of sonar to detect fish in rivers. And in the more than 40 years that ADF&G has used sonar in rivers, its tools and methods have progressed to provide increasingly more detailed information about sonar-detected fish.

Today ADF&G uses three types of sonar technology—Bendix sonar, split-beam sonar and, our latest generation of sonar technology, DIDSON. Today we rely almost entirely on DIDSON. Out of 15 ADF&G sonar sites, 11 sites use DIDSON exclusively, one site uses Bendix sonar exclusively, while three sites use a combination of split-beam and DIDSON.

Bendix Sonar Split-Beam DIDSON
Key: Yes No No No

Bendix sonar is the first and longest running sonar technology to count fish in Alaska rivers. ADF&F has retired Bendix at all but its Crescent River sonar site, where it counts sockeye.

ADF&G uses split-beam at two Yukon River sonar sites and a Kenai River king salmon site. These sites require long-distance fish detection, a task split-beam sonar excels at.

DIDSON was developed for military underwater mine and diver detection. Since ADF&G first tested DIDSON for detecting fish in 2002, it has advanced sonar fish detection considerably.

Detection method Counts echos Produces fish traces Produces high-resolution fish video
Max distance of fish detection ~30 meters ~300 meters ~40 meters
Determines fish travel direction No Yes Yes
Can be used to calculate fish size No No Yes
Identifies Fish Species No No No

» More About Bendix

» More About Split-Beam

» More About DIDSON

How sonar technology works

The basics of how sonar finds fish in a river are simple. First a sonar transducer submerged in the river emits a beam of sound waves into the water. When the sound waves encounter an object with a density different than water, such as a fish’s swim bladder, some of the sound waves bounce back to the transducer as echoes. The transducer detects these echoes and fisheries biologists then analyze transducer data to provide information about fish in the river.