Application of a Dual Beam Echo Sounder to Measuring Fish Length

Abstract

This paper discusses the application of a dual beam echo sounder to the estimation of fish length. The dual beam method is typically used for measurement of the in situ target strength of fish. The in situ target strength is an important parameter, not only for obtaining the echo integrator scaling factor but also for estimating the fish length that is related to target strength. A prototype dual beam echo sounder system with computer technology was developed and used in the acoustic survey conducted at Lake Kuttara. Kokanee Oncarhynchus nerka is abundant in this lake. Many individual echoes were recorded using the dual beam echo sounder and target strength data were collected. Converting target strength, TS, into body length, 1 was done using the following relational formula: TS (dB)=20 log l (cm)-66.0 Results of the analysis indicated that both the distributions of target strength and body length which were estimated by the dual beam method agreed to the catch data obtained from net sampling. © 1991, The Japanese Society of Fisheries Science. All rights reserved.