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  • Writer's pictureEric Munday

Salmon and Sonar in Seattle

Updated: Aug 28, 2023

Pacific Northwest salmon show toughness, BioSonics keeps a count


This summer saw a spectacular run of Chinook and other salmon species return to the Salish Sea and it’s tributaries. Lucky visitors at the Ballard Locks in Seattle were treated to a dazzling visual display as hundreds of mature Chinook and sockeye traversed the fish ladder daily during the peak of the spawning run in August. Spectators lined the railings and packed the viewing windows to watch as stacks of 20-plus pound Chinook moved slowly but steadily upstream through and over the ladder. Upon exiting the ladder and now in fresh water, the fish swim over five miles through the bustling city of Seattle, through the Ship Canal and Lake Union and into Lake Washington. From there, the salmon may continue 40 or more miles to their home stream or river.

Northwest salmon are truly tenacious. After surviving several years in the open ocean, salmon navigate from as far away as Alaska while returning to their home estuary and origin river. In the rivers they are likely to encounter jagged rocks and fight strong currents until, completely exhausted with flesh beaten and skin mottled dark and scarred, they reach their spawning grounds and complete their life cycle. Throughout their life history and especially during spawning migration, salmon must avoid a range of predators including ravenous bears, raptors with razor sharp talons, cunning marine mammals, and the hooks and nets of eager fishermen. Evidence of the hazards encountered by these fish was ample during a recent visit to the Ballard Locks. The images below were captured during a few minutes of observation at the fish ladder.

Mature Chinook with bite mark, likely from a sea lion or seal.






This salmon was lucky, the line snapped after being hooked.


An unlucky salmon just became lunch for this seal who was hunting just outside the fish ladder entrance


Another tenacious Pacific Northwest entity is Seattle-based sonar manufacturer BioSonics. The company has been manufacturing specialized sonar for scientific fisheries applications since 1978, and they are quite “well positioned” to monitor salmon. Indeed, their waterfront headquarters are less than 900m upstream from the Ballard Locks and fish ladder. As salmon pass directly in front of their facility, company President Tim Acker studies the annual migration event by deploying a DT-X split beam echosounder from the pier at his research facility. A horizontally aimed transducer detects each fish passing through the sonar beam and the acoustic data provides a running count of total fish passage as well as the size, location, and speed/direction of travel of each fish. The DT-X system operates continuously during the migration period, providing valuable information on the timing and total abundance of the return.


Shown below is the DT-X echosounder in an environmental housing next to a transducer pole mount and WiFi antenna. Data is streamed wirelessly to a shore-based PC connected to a big screen monitor where BioSonics scientists can easily view the echogram and keep track of fish traffic throughout the day.


BioSonics proprietary AutoTrack software automatically processes the acoustic data and creates track lists in csv file format, thus greatly reducing the data processing effort and providing usable, scientific information in near real-time.AutoTrack can be configured to track and send alerts based on size, speed, and/or location and is used for monitoring fish, jellyfish, or drifting vegetation and debris. In the video below you can see dozens of salmon represented by the green pixels that form fish tracks in the sonar echogram.


BioSonics DT-X echosounder and AutoTrack software are powerful tools for underwater detection and early warning applications. The platform is easily configurable and suitable for long term studies.


Contact us for more information!

Inquiries from North America call 206 782 2211 or click here

International inquiries, call 800 SUBSEA1 or click here



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