Target strength for fish identification using echo sounder

Abstract

Identification of target strength (TS) of fish species in the South China Sea has been conducted using Furuno FQ-80 (38/120 kHz echo sounder). This study introduces new experimental method which is combination of in situ and ex situ experiment by applying net cage at undersea. This cordyla (Torpedo scad) in separate net cage at the bottom of the vessel. TS, depth, and position (x-y-z) of fish have been monitored at every ping using echogram. TS of Selar boobs at low and high frequency are -44.49 dB for source level (SL) of 236dB and -43.96 dB for SL of 228 dB. For Megalaspis cordyla, TS are -45.34 dB (SL = 230 dB) and -43.06 dB (SL = 225 dB) for low and high frequency respectively. The results show that Megalaspis cordyla produce higher TS whereas the position is deeper and smaller size than Selar boops at low and high frequency.