. Commercial fisheries review. Fisheries; Fish trade. 47. Fig. 1 - Schematic illustration of sonar beam pattern initiating fish school echoes during scans: (1) center of sonar beam ap- proaching fish school, (2) center of sonar beam passing beyond fish school, (f J center line of sonar beam as indicated by trans- ducer bearing indicator, (a i) leading edge of sonar beam with su:Sicient acoustic power to generate a detectable fish-school echo trace, (b2) trailing edge of sonar beam with sufficient acoustic power to generate a detectable fish-school echo trace. fe\ 4 ^: ^''^OX: N^ ~^^ ^ 4 ^^ Fig
. Commercial fisheries review. Fisheries; Fish trade. 47. Fig. 1 - Schematic illustration of sonar beam pattern initiating fish school echoes during scans: (1) center of sonar beam ap- proaching fish school, (2) center of sonar beam passing beyond fish school, (f J center line of sonar beam as indicated by trans- ducer bearing indicator, (a i) leading edge of sonar beam with su:Sicient acoustic power to generate a detectable fish-school echo trace, (b2) trailing edge of sonar beam with sufficient acoustic power to generate a detectable fish-school echo trace. fe\ 4 ^: ^''^OX: N^ ~^^ ^ 4 ^^ Fig, 2 - Schematic of measurements of fish school taken from aerial photograph; school angle (â ©), school width (W), and school length (L), superimposed over measurement of the same fish school determined from sonar data; scan angle (9), sonar trace length (Y), calculated school length (X), and school range from the vessel (R), dimensions from the photographs were used because these dimensions more closely ap- proached the type of data obtained from the sonar. Figure 2 shows the method used to obtain fish school dimensions from photo- graphs and to reconstruct school dimensions from sonar data. The sonar tape provided an estimate of school range and school width along the sonar beam axis. The degrees of arc occupied by the fish school (scan degrees) were read di- rectly from the sonar transducer bearing in- dicator and were recorded during each scan of a fish school. Using this sonar data we could estimate greatest horizontal length, perpendicular to the sonar beam for the school by the formula L = R tan 0 where: L = school length (feet) i) - scan angle (degrees) R = range or distance (feet) from the sonar transducer to the near side of the fish school RESULTS The range and estimated horizontal school widths from the sonar traces appeared to be within the limits of measurement error when compared with the school dimensions from â ;he aerial photographs. Apparently the k
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