MEPS 180:105-109 (1999)  -  doi:10.3354/meps180105

Acoustic measurements of zooplankton using a dual frequency echo sounder

K. Miyashita*, I. Aoki**

Ocean Research Institute, The University of Tokyo, Minamidai, Nakano, Tokyo 164, Japan
Present addresses:
*Laboratory of Training Ship, Faculty of Fisheries, Hokkaido University, Minato, Hakodate, Hokkaido 041-8611, Japan. E-mail:
**Department of Aquatic Bioscience, Graduate School of Agricultural and Life Science, The University of Tokyo, Bunkyo, Tokyo 113-8657, Japan

ABSTRACT: Two methods for acoustic estimation of zooplankton abundance using the difference in volume back-scattering strength (SV) at 2 frequencies between 38 and 200 kHz were examined in a situation where the biological composition was simple. Method 1 used the SV difference, and Method 2 used both SV difference and body length data from net samples. The high-pass sphere model and straight cylinder model were applied depending on dominant target species: when they were relatively small, such as copepods, the high-pass sphere model was used, and when adult krill were dominant the straight cylinder model was used to take the swimming angle of the adult krill into consideration. Acoustic estimates were compared with net samples. Using the high-pass sphere model, Method 1 provided plausible estimates of zooplankton size and biomass, and Method 2 provided better biomass estimates. Furthermore, it was shown that by using the straight cylinder model and swimming angle distribution, Method 1 can be applied to obtain estimations of the krill's size and biomass.

KEY WORDS: Dual frequency method · Zooplankton · Echo sounder

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