Food Poisoning Due to Ingestion of the Puffer Lagocephalus lunaris

Abstract

The relationship between backscattering strength and fish density isa scaling factor of quick acoustic assessment method.It will affect theaccuracy of estimating results.In fact,engraulid larva(anchovy)is so weakand small,it is impossible to form simulating school by using live fish.Thedead fish used to simulate fish school by sinking through a 0.83 cm×0.83 cmmesh size sifter in anechoic tank is described in this paper.Fish density rangingfrom 170 inds./m^(3)to 14,226 inds./m^(3)were insonified by a pressure pulse at acarrier frequency of 200 KHz.The received echo signals were recorded onmagnetic tape,digitized and processed in a microcomputer to obtain theaverage backscattering strength of each model school.In a joint effort withunderwater optical method to determine the instantaneous actual fish densityof model school.The results are summarized as follows:(1)The average backscattering strength is in proportion to the densityof the model school under 1000 g/m^(3).Below this critical density,it is possibleto estimate the standing crop of engraulid larvae by quick acoustic assessmentmethod.(2)The individual target strength of engraulid larva is weak rangingmore or less between-101.8dB and-94.1dB.Therefore,the fish densityrecorded on the echogram by echo sounder is very light.(3)The regression line between the average target strength(Ts)andand the logarithm of mean body length(BL),Ts=26.42 Log(BL)-110.65,isobtained from this study,with a correlation coefficient of 0.98.