魚群探知機記録の解析-7 : 魚の遊泳速度

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タイトル別名
  • ギョグン タンチキ キロク ノ カイセキ 7 サカナ ノ ユウエイ ソクド
  • Analysis of Fish-Finder Records―VII Swimming speed of fish

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An echogram from an ultrasonic fish-finder appears to be an acoustic section of the sea, showing the distribution of fish in great detail from the surface to the deep 6). Therefore, the analysis of information obtained by a fish-finder for the purpose of studying the ecology of fish, i. e. size, abundance, swimming depth and speed of fish, is very important matter for fishermen. This paper deals with the method of estimation of swimming speed of fish from echo trace of vertical fish-finder. Equations for estimating the swimming speed of fish are as follows. 1) General solution VF=-h1.cosα-Vs.t.sinα+√h2.cos2α+(Vs.t)2sin2α-2h.Vs.t.sinα.cosα-h2+h21-(Vs.t)2/t 2) When swimming direction is only horizontal, α=π/2, VF=√h21-h2/t-Vs 3) When swimming direction is only vertical, α=0, VF=√h21-(Vs.t)2-h1/t where, VF and Vs are the speed of fish and fishing boat per unit time respectively, α is the subtended angle of swimming direction to perpendicular, h1 and h, respectively are the depths at the beginning of recorded echo trace of individual fish and the shallowest depth recorded on it. and t is the time requiered between h1 and h. The author analyzed the data of acoustic observations made in the Northwestern Pacific Ocean from 1961 to 1966 through use of a fish-finder installed on Nagasaki-Maru of Nagasaki University and estimated the speed of tuna crossing the sound beam of the 14kc fish-finder. The speed of tuna like fish ranged from 0.05 knot to 15 knots but mostly from 0.05 to 4 knots.

長崎大学水産学部研究報告, v.25, pp.59-65; 1968

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