Alaska Fisheries Sonar

Alaska Fisheries Sonar
Sonar Technology Tools

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ADF&G uses imaging sonar (DIDSON and ARIS) to record ultrasound-like fish video. Imaging sonar can also be used to size fish, and ADF&G biologists have also tested 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. 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.

Since the program began, ADF&G has used three types of sonar technology—Bendix sonar, split-beam sonar and imaging sonar (DIDSON and ARIS). Today we rely almost entirely on imaging sonar, as all Bendix sonars have been replaced with imaging sonar units. Out of 15 ADF&G sonar sites, 12 sites use imaging sonar exclusively, while two sites use a combination of split-beam and imaging sonar.

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

Bendix sonar was the first and longest running sonar technology to count fish in Alaska rivers. ADF&G has replaced all Bendix sonars with newer sonar technologies.

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

DIDSON was developed for military underwater mine and diver detection. DIDSON and ARIS (the latest generation of DIDSON technology) have advanced sonar fish detection considerably.

Detection method Counts echoes Produces fish traces Produces high-resolution fish video
Max distance of fish detection ~30 meters (approx. 100 feet) ~300 meters (approx. 985 feet) ~40 meters (approx. 130 feet)
Determines fish travel direction No Yes Yes
Can be used to calculate fish length No No Yes
Identifies Fish Species No No No

» More About Bendix

» More About Split-Beam

» More About Imaging Sonar

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.