ANCHOVY DISTRIBUTIONAL PROPERTIES BY TIME AND LOCATION: USING ACOUSTIC DATA FROM A PRIMARY TRAWL SURVEY IN THE SOUTH SEA OF SOUTH KOREA

Abstract

In South Korea, acoustic data from primary trawl surveys are not exploited. Thus, the objective of this study was to present the availability of acoustic data from a primary trawl survey by examining the distributional properties of anchovy schools by time (morning and afternoon) and location (inshore and offshore). Echosounder data were collected while conducting a trawl survey in the South Sea of South Korea on April 14-18, 2014. In six of eight trawl shots, the major species was anchovy Engraulis japonicus (> 95% of total catch weight). Consequently, the length, thickness, area, and volume back scattering strength (Sv) of morning and afternoon anchovy schools were similar; however, some afternoon schools were very long or thick. Morning schools were distributed in a wider depth range than were afternoon schools. All distributional properties, other than the length and area, differed significantly by time (Mann-Whitney U test, p < 0.05). A comparison between anchovies in inshore waters and mixed species schools in offshore waters, the average length of the inshore anchovy schools was longer than that of the offshore schools, whereas the average thickness, area, and Sy of both schools were similar. Long or large schools were observed only in inshore waters. Inshore schools were distributed at a deeper depth than offshore schools. Every property, except Sy, differed significantly between inshore and offshore waters. Finally, a conceptual diagram is presented to illustrate the distributional properties of anchovy schools according to time and location.