Assessment of biomass in artificial reef area of Yangmeikeng in Daya Bay using acoustic method

The Yangmeikeng artificial reef area is located in the eastern part of Daya Bay in Shenzhen.The artificial reefs were cast from March 20,2007,and the whole construction was finished on December 25 with the volume of 95.1 thousand m³ space and the area of 966 m?2 851 m.In order to know the biological distribution and the variation of the biomass density,six acoustic surveys were conducted with a split-beam echosounder(EY60 model,120kHz,Simrad)inside and outside the artificial reef area of Yangmeikeng in Daya Bay in different months from April 2007 to May 2009.The effective acoustic range is 122.54 n mile.Trawl samplings were used to help the acoustic assessment.In this paper,the volume backscattering strength(SV)data were integrated with 0.5n mile interval to analyze the distribution of biomass by using a fisheries acoustic software of Echoview(Myriax)combined with the historical data of ecology,resource characteristics and trawl data.The acoustic assessment results showed that the average biomass density inside and outside the artificial reef area were 41?10³ kg/n mile² and 28?10³ kg/n mile² respectively in survey 1,while 16?10³ kg/n mile² and 10?10³ kg/n mile² in survey 3,65?10³ kg/n mile² and 3?10³ kg/n mile² in survey 4,165?10³ kg/n mile² and 45?10³ kg/n mile² in survey 5.Obviously,the average density of biomass was higher inside the artificial reef area than the outside.And the inside biomass assumed the growth movement basically as time goes on.According to the trawl sampling data,the species estimated inside the artificial reef area were also increased evidently,such as Siganus canaliculatus and Nemipterus japonicus. It proved that the construction of artificial reefs in the Daya Bay could improve community structure of fishery resources.