Acoustical Survey for Estimating Fish Biomass at Chilam Bay, Korea

Abstract

Acoustics is effective method in fisheries research studies involving direct biomass estimation. Fish biomass change in space and time and fish populations dynamics are attributed to under water construction with artificial reefs in marine ecosystem. This study estimated fish distributions, determined catch composition, and biomass changes in small scale marine ranching area during daytime and nighttime using the scientific echo sounder and the gill net. Fish were densely distributed in pelagic zones during nighttime than daytime where few fish schools were scattered near sea bottom. In each season’s gill nets 15 different groups of fish species were caught and their estimated average target strengths were -44.0 dB and -44.4 dB for autumn and winter surveys, respectively. The autumn biomass were 7.7 and 26.0 tons during daytime and nighttime, respectively. Winter had 2.27 and 30.97 tons during daytime and nighttime, respectively. Different species are more active at night, and exhibit movements and behaviours thus occupy varying water zones. This explains the varying estimated biomass with seasons and time of surveys around artificial reefs. Comprehensive studies about fish biometrics and demersal species to accurately estimate entire biomass of all fish species in Chilam Bay will be carried out in future.