Fisheries Stock Assessment
Learn the Basics
BioSonics DT-X mobile echosounders are widely used to determine fish population and sizing distribution in lakes, reservoirs, rivers, and coastal waters. Other applications include zooplankton biomass estimation, school size estimation, and behavioral studies. The portable DT-X is easily deployed from a small boat using a convenient swivel mount to attach and aim the transducer. The transducer is typically oriented vertically and used to scan the water column in a series of transects to collect information on fish size and distribution. All data is georeferenced using an integrated DGPS sensor.
Methods for mobile hydroacoustic assessment of fish population are well established and widely accepted by regulatory agencies based on decades of scientifically verifiable and consistently accurate results. Large areas can be covered quickly and with relatively low effort, making this an extremely cost effective technique.
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How It Works
Fisheries hydroacoustics involves the use of sound to detect and quantify aquatic organisms. Scientific split beam echosounders are now the standard instrument of fisheries hydroacoustics. These instruments operate on the same principles as a recreational or commercial fishfinder or echosounder, but are engineered for greater accuracy and precision, allowing for quantitative biomass estimates. In order to be used for quantitative work, scientific echosounders are calibrated. Calibration is checked before and after each survey by examining echoes from a metal calibration sphere with known acoustic properties.
The echosounder transceiver generates a short pulse of energy which is sent into the water by the transducer to produce a focused beam of sound. As sound encounters objects, such as fish, that are of different density than the surrounding medium, some sound energy is reflected back toward the source. These reflected echoes provide information on fish size, location, and abundance. By comparing the phase difference of the same echo, split-beam echosounders can accurately determine the location of each target in the acoustic beam in three dimensions. This allows for highly accurate measurement of each targets reflective strength. Target strength (TS) is a measurement of how well a fish, zooplankter, or other target scatters sound back towards the transducer. Target strength is of critical importance in fisheries acoustics, since it provides a link between acoustic backscatter and animal biomass. Accurate conversion of TS data to animal size or population abundance is how fisheries resource managers and researchers obtain useful information using hydroacoustics.
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