A tracking transducer for following fish movement in shallow waterand at close range

Abstract

Shallow water studies of fish behavior have used various methods for tracking fish. A new technique is shown to be promising because it can combine acoustic sizing with fish behavior studies. The principle of radar tracking, aligning the antenna beam with a target, was applied with an acoustic splitbeam transducer and dual-axis rotators for tracking individual fish over long periods of time. Deviation of the target from the beam axis produces a correction to point the axis toward the target. Initial studies with active acoustics have also evolved an acoustic tag tracking method. The system has successfully tracked several different types of fish, from juvenile salmon to sharks. The high speed of the rotators allows observations to be made at very short ranges. Much of the development of the tracking transducer targeted fish movement through dams on the Columbia and Snake Rivers. In a recent experiment, adult salmon, returning to the Fraser River, Canada were tracked to measure avoidance to surveying vessels. The feasibility for tracking sharks was shown at the Tacoma WA Point Defiance Aquarium. A proposed method for tracking salmon, sharks or other species with echoes and/or using acoustic tags will allow the determination of behavior, acoustic size, abundance, and associated pelagic assemblages.