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Alaska Department of Fish and Game


Alaska Fisheries Sonar

Anvik River
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Anvik sonar images
A counting tower installed alongside the right bank sonar transducer is used to determine how many of the sonar-detected fish should be counted as chum salmon (upper right). Technicians take scale samples from a chum salmon captured with a beach seine net (right).

Site technicians cannot use sonar to distinguish fish by species. To help biologists determine how many of the sonar-detected fish should be counted as summer chum salmon they observe fish from a counting tower installed near the transducer. Technicians count fish from the tower four times a day. Biologists then examine the number of chum salmon counted relative to other species to determine how many of the sonar-detected fish should be counted as chum salmon. Tower counts are also used to help verify the sonar counts.

In addition to using sonar and a tower to count and separate fish by species, site technicians also use beach seine nets to capture fish for data collection and scale sampling. Technicians beach seine just downstream of the sonar site three times per week, tallying and recording captured fish by species before releasing them. Before the chum salmon are released, technicians record length, gender and take a scale sample. The scale samples can be analyzed to determine age, and biologists use the gender, length and age information to identify long-term trends in Anvik summer chum runs. If any king salmon are caught, they are sampled using the same methods as for chum salmon.