ICES Journal of Marine Science · 1996 · 120 citations · 4 references
EngineeringFisheriesZoologyAcousticsFish BiologyUnderwater AcousticsAcoustic EcologyAcoustic Sensing SystemsSonar SystemsAcoustic Monitoring Of FishAcoustic SurveysEcho Sounder ApplicationsExperimental AcousticsSonar Sensors
Biases in measuring fish school spatial distribution and biomass during conventional acoustic surveys arise mainly from vertical and lateral avoidance of the vessel. This study quantifies school avoidance during an acoustic survey in the Catalan Sea from 13–29 May 1994. Using a 60‑beam multi‑beam sonar (1.5° × 15°) that scanned a vertical plane perpendicular to the vessel, the authors measured geometric characteristics of 1,268 schools and simulated the echo‑sounder’s ensonified area for comparison. The analysis revealed how avoidance patterns depend on school size, structure, and depth, and quantified the vessel’s impact on echo‑sounder biomass estimates.
Biases in the measurements of spatial distribution of fish schools and their consequences for school biomass estimates during conventional acoustic surveys are mainly due to vertical and lateral avoidance of the vessel. In this paper, we quantify school avoidance during an acoustic survey carried out from 13 to 29 May 1994 in the Catalan Sea. From a lateral multi-beam sonar the geometric characteristics (depth, length, width, height, surface, and volume) of 1268 schools were obtained. The 60 beams (1.5°×15°) of the sonar scanned a vertical plane from 0° to 90°, perpendicular to the vessel path within a range of 100 m. Within this plane, the projected area ensonified by the echo-sounder used aboard for acoustic evaluation was evaluated to simulate a comparison between the sonar and the echo-sounder. The results have enabled us to improve our knowledge on the vertical and lateral avoidance patterns of schools in relation to their size, external structure, and their position in the water column, and to quantify the vessel influence on biomass estimated by echo-sounder.
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