Measurement of the target strength of Japanese flying squid, Todarodes pacificus steenstrup
1999
Kawabata, A. (Tohoku National Fisheries Research Inst., Shiogama, Miyagi (Japan))
The Japanese flying squid, Todarodes pacificus Steenstrup, is one of the most important commercial species for coastal fisheries in the northeastern Pacific off Japan. There is difficulty in determining the catchability coefficient of catch survey gear for estimating squid biomass. Estimation of squid biomass in fishing grounds by acoustic survey would allow more reliable estimations. However, the target strength of squid is necessary for estimating squid biomass acoustically. Measurement of target strength of Japanese flying squid was made using both preserved and live squids in fishing grounds by an in situ method with a split-beam echo sounder at 38 kHz. Preserved squids gave values of low availability for estimating biomass, because the body orientation and physical characteristics were different from live squids. Values of in situ target strength for live squids were estimated during 4 surveys. The relationship between the target strength (TS) and the squid mantle length (Ml) was determined as follows: TS (dB) = 40.9*log ML(cm) -94.2 (r=0.98, ML; 18-24cm) The values obtained were higher than those reported in some previous studies for live squid. The possibility of an overestimation cannot be ruled out, because the values were estimated in waters where squids were distributed at high densities
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