Assessment of fish spatial distribution and biomass in Lake Taihu using hydroacoustic method

Before the fishing of Lake Taihu,a mobile hydroacoustic survey was performed in eastern and northern of Lake Taihu in August of 2011,with using BioSonics DT-X scientific echo-sounder(208 kHz).Combining Geographic Information System(GIS) model,then fish size component,spatial distribution and biomass are assessed.The results show that the mean target strength(acoustic reflectivity of target fish) in the surveying lake areas is-51.85±0.02 dB and the mean length is about 6cm,ranging from 2.35 to 89.33 cm.The fish target strength in different areas is significantly different,which means there is significant difference of fish size,with the minimum mean target strength(-53.94±0.10 dB) in the middle of Dongshan Island and Xishan Island and the maximum mean target strength(-50.27±0.14 dB) in Guangfu Bay.The mean fish density is 2.27±0.57 ind./m3,ranging from 0.43 to 3.90 ind./m3 in all survey areas,where a high fish density occurred in open water zone.Based on the raster data gained from fish distribution GIS model,the total amount of fish mantissa biomass are estimated to be 5.3×109 ind.,in which the fish with target strength lower than-45 dB(length about 13cm) is 98.49%.The present study provided a preliminary application of the hydroacoustic method and performed in big shallow lake for fish resources investigation.This can break through the limitations of the traditional investigation methods for fish resource assessment on large spatial scales,to a certain extent.The application is still influenced by stormy waves,aquatic plants and speed.