Application of the acoustic method in biomass estimation of multi-species fisheries
                                 in the South China Sea

  Rosidi bin Ali*1, Raja Bidin bin Raja Hassan*1, Albert Chuan Gambang*2, Samsudin 
        bin Basir*3, Hadil bin Rajali*2, Kunimune Shiomi*1 and Shunji Fujiwara*1


	*1 SEAFDEC/MFRDMD, Fisheries Garden, Chendering, 21080 Kuala
	   Terengganu, Terengganu, MALAYSIA
	*2 Fisheries Research Institute, Bintawa, 93744 Kuching, Sarawak, MALAYSIA
	*3 Fisheries Research Institute, 11960 Batu Maung, Penang, MALAYSIA


     This paper presents the  approaches and the findings of the acoustic surveys  in 
estimating  the fish  biomass  of multi-species  fisheries, in  waters  of the  Gulf  of 
Thailand waters  and the east  coast of Peninsular  Malaysia, based on  two acoustic 
surveys that were carried out  with M/V SEAFDEC in those areas. The first  survey 
was conducted  on the 5.9.1995  yp 28.5.1995(i.e. the pre-Northeast  monsoon season), 
and the second survey was done on the 24.4.1996 to 17.5.1996 (i.e. the post-Northeast 
monsoon  season). The  scientific echo-sounder  installed on  board M/V  SEAFDEC, 
FQ-70 (Furuno Electric Co.), was employed in the surveys.
     The  erroneous SV  values collected  by the  200 kHz  transducer were  careful 
examined and were deleted. For the pelagic fish, there  was a significant difference in 
the distribution  of SV  values of  the pre-monsoon  compared to  the values  of the 
post-monsoon.  The  high SVs were observed  in the pre-monsoon survey, from  the 
off-shore to the near  shore waters. However, the high SVs was  not detected in the 
post-monsoon  survey.  In  case  of  the  demersal  fish, there  was  no  significant 
difference  in the  distribution of  SV values  of  the pre-monsoon  compared to  the 
values of the  post-monsoon. The higher SVs were observed  in the northern part of 
the Gulf of Thailand and a long the east coast of Peninsular Malaysia.
     For  the biomass  estimation, the  representative  species of  demersal fish  and 
pelagic fish from the Gulf of Thailand and the representative species of demersal fish 
and  pelagic  fish  from  the  east  coast  of  Peninsula  Malaysia  were  determined 
separately. The  information on  length and  weight of  these species  were gathered 
from the  annual catch statistics and  from the in-situ  surveys at the landing  place. 
The  target strength  (TS) of  these species  were calculated  based on  the average 
standard length. 
     The estimated biomass of fish in the Gulf of Thailand for  the pre-monsoon and 
the post monsoon  seasons were 9.2 x 105  tones (i.e. 5.5 x 105  tones of pelagic fish 
and 3.7 x  105 of demersal fish)  and 4.7 x 105  tones (i.e. 2.0 x 105  tones of pelagic 
fish and 2.7 x 105 tones of demersal fish) respectively.
     The estimated biomass of  fish off the east coast of Peninsula  Malaysia for the 
pre-monsoon and post-monsoon seasons were 4.4 x  105 tones (i.e. 2.3 x 105 tones of 
pelagic fish and 2.1  x 105 tones of demersal fish) and 3.2  x 105 tones (i.e. 1.9 x 105 
tones of pelagic fish and 1.2 x 105 tones of demersal fish) respectively.