Study of Pelagic Fish Target Strength Distribution in Mentawai and Southeast of Enggano Seawaters Using Split-beam Acoustic System

Abstract

An acoustic survey on pelagic fish was conducted in Mentawai and southeast Enggano seawaters in March 1999 and December 1999. The SIMRAD EK 500 split-beam acoustic system with frequency of 38 kHz was used for collecting acoustic data and CTD for oceanographic data The stations of 13 and 10 were fixed along triangular cruising transects at Mentawai and Enggano seawaters respectively. The obtained data were analysed and the results show that dominant single fish was detected in Mentawai water at sirata-3 of 100-150 m depth with total single target of 4164 fish. Target strength values were ranged from -50 to -32 dB, with dominant TS value of-50 dB from the fish near the surface In southeast Enggano water, the detected single target was dominant at strata-2 of 44-84 m depth with total single target of 245 fish. The target strength values range were -50 to -41 dB. The dominant target strength values at all stations is around -50 dB. The relationship between ooeanographic parameters (temperature and salinity) with single fish distribution was found at 15.0-16.0UC and 35.0-36.0 %, at station near the coast; 14.5-16.5°C and 33.8-34.0 at station far from the coast in Mentawai water. In southeast Enggano water they were 27.5-29.0 and 33.6-33.9 %0 at station of South latitude 6.00°; 27.5-28.0°C and 33.7¬33 8 %0 at station of South latitude 6.20°