Development of a quantitative scanning sonar system and sea trial for a fish school of herring

Abstract

A quantitative sonar system enabling data recording, calibration, and numerical analysis of fish schools was developed based on the commercial scanning sonar. This system is equipped with a newly developed algorithm for estimation of the abundance of a fish school using three-dimensional echo integration. Estimation was made on the condition that the target strength of all fish is identical and known and the weight of a single fish is known. The field recording was performed to evaluate the algorithm. The school of spring spawning herring were scanned three-dimensionally and recorded using two different scanning methods. Two methods were applied in different distances between the school and vessel. The volume and three-dimensional echo integration for these two recorded dates were calculated and compared to each other. It was found that the variance of three-dimensional echo integration is smaller compared with the variance of volume. A compensation of abundance estimation using average target strength was tried and its effectivity was examined.