Active tracking sonar study of salmon migration behaviour at Mission, British Columbia, 1998 / G.M.W. Cronkite, Y. Xie, and A.P. Gray.: Fs97-4/2506E-PDF

"An experimental active tracking acoustic system was used at Mission, B.C. to study salmon migration at this site in an attempt to detect fish reaction to an approaching survey vessel used in the Pacific Salmon Commission's regular echosounding programme. The active tracking split-beam system is useful for tracking fish movements over a much larger three-dimensional space than is possible with a fixed-aim split-beam system. We gained information on fish behaviour and acoustic measurements and we documented some interesting fish behaviour at the site. The active tracking split-beam sonar system gives precise information on direction of travel and speed of fish targets. The active system centres its acoustic axis on a moving target and follows the target, thus minimising the position bias caused by lower signal-to-noise levels when the target is located near the edge of the sound-beam. We have documented the position bias effect of a fixed-aim split-beam sounder on both the speed and swimming angle measurements of fish targets by comparing similar measurements acquired with the active tracking split-beam system. It is useful to measure the magnitude of this bias effect in the riverine environment. We did not obtain the definitive answer on the presence or absence of boat avoidance behaviour. In the portion of the river cross section surveyed by the active system, the boat avoidance effect did not appear to be pronounced. We also showed the importance of aiming the acoustic axis perpendicular to the fish passage to maximise fish detection"--Abstract, page iv.

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