曳網速度の違いによるプランクトンネット採集効率の差

概要

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The catch efficiency of a 24.9cm BONGO net on anchovy larvae Engrauris japonicus was examined at three different towing speeds: low speed (about 0.8m/sec: L), middle speed (about 1.3m/sec: M), and high speed (about 1.8m/sec: H). The ratio of catch efficiency, which is equivalent to capture probability multiplied by mesh retention, was calculated at M speed to at H speed (EM/EH) and at L speed to at H speed (EL/EH) from the catch data of larvae. In the daytime, EL/EH decreases as the size of the larvae increases, and this value was 0.94-1.09 over an interval of 2.5-3.5mm in S.L., and 0.67-0.87 over an interval of 4.5-9.5mm in S.L. Although EM/EH in the daytime decreases as the size of larvae over 7.5mm in S.L. increases, it is bigger than 1, 1.04-1.49, over an interval of 2.5-6.5mm in S.L. At night, EL/EH changes a little, 0.93-1.12, over an interval of 2.5-8.5mm in S.L. and decreases as the size of the larvae over 9.5mm increases in S.L. These results suggest that capture probability does not always increase as the towing speed increases, and that small larvae can not avoid plankton nets at night.
日本水産學會の論文