魚群探知機の記録から魚群の游泳速度を測定する一つの試み(予報)

概要

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The swimming speed of fish schools passing through the entrance of a set net has been calculated on the basis the recorded figures on a linear system fish finder. The methods used for the calculation are as follows. When the transmitting and receiving oscillators are fixed slantingly downwards to the entrance of a set net (Fig. 1), the recorded figure of fish schools passing through the entrace of the net may be estimated in a line as indicated figure 2. If we set the angle of inclination of recorded figure “ab” towards the axis of time “T” is represented by “α”, the approximate swimming speed “S” of fish schools will be formulated as S ?? (v/h)tanαsecγ where S: swimming speed of fish schools, v: conveying velocity of recording paper, h: reduced scale of recorded figures, α: the angle of inclination of recorded figure toward the axis “T”, γ: the angle of inclination formed by the projecting direction of ultrasonicwave and water surface. As the result of field test which was carried out at night applying the above method to a set net commercially operated for horse-mackerel. The swimming speed of the fish schools horizontally swimming in and out of the net has been estimated to range from 0.05 to 0.55m/sec (Table 1 and Fig. 5).
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