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

Abstract

利用BioSonics DT-X科学回声探测仪(208 kHz)在太湖2011年开捕前的8月对东部和北部湖区的鱼类进行了走航式水声学调查,并结合地理信息系统(GIS)模型对调查湖区的鱼类大小组成、空间分布和资源量进行了评估.结果表明,调查湖区的鱼类平均目标强度(目标鱼类对声波的反射能力)为-51.85±0.02 dB,平均体长在6 cm左右,体长范围为2.35~89.33 cm,不同区域间的鱼类目标强度差异性显著,表明不同区域间鱼类大小存在差异,其中鱼类的最小平均目标强度(-53.94±0.10 dB)出现在洞庭东西山之间,最大平均目标强度(-50.27±0.14 dB)出现在光福湾.调查湖区的鱼类密度在0.43~3.90 ind./m³之间,采用地理信息系统(GIS)对调查湖区进行建模得到鱼类密度均值为2.27±0.57 ind./m³,不同区域间鱼类密度差异性显著,鱼类密度在敞水区较高.基于建模的栅格化数据评估调查湖区鱼类资源量约为5.3×10⁹ind.,其中目标强度在-45 dB(体长约13 cm)以下的鱼类占98.49%.本文对水声学方法在大型浅水湖泊中的应用进行了初步探索,水声学方法可在一定程度上突破传统鱼类资源调查方法在较大空间尺度上的局限性,但在调查时易受风浪、水生植物、船速的影响.;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 6 cm,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 13 cm) 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.