Acoustic approach for estimation of Skipjack (Katsuwonus pelamis) abundance in Bone Bay

Abstract

Skipjack is one of the most important economical fish. As a result, skipjack stocks are vulnerable to over-exploitation. Therefore, to anticipate and to set sound management plan, it is necessary to monitor from time to time the abundance of these fish to ensure the sustainability of its resources. The purpose of this study was to determine the abundance distribution of skipjack fish based on acoustic method in Bone Bay waters. The abundance estimate of the skipjack was conducted using Split Beam Echosounder Simrad EY 60 with frequency 120 kHz. The results of this study indicated that the range of skipjack target strength (TS) was -67.0 dB to -55.3 dB, or equivalent to fish length of 8 cm to 31 cm, detected from surface to a depth of 40 m. Temporally, skipjack density during the day was more towards the surface with an average of 43 ind/1000m3 and at night in deeper waters with an average density of 36 ind/1000m3. Vertically, the highest density was detected at a depth of 5 m - 15 m with a density of 82 ind/1000m3. While horizontally, the highest skipjack density of 188 ind/1000m3 was found around Kolaka waters.