Measurement of Dorsal Aspect Target Strength of Live Swimming Crab Portunus trituberculatus Caught in the East China Sea.

The dorsal aspect target strength (TS) of four live swimming crab Portunus trituberculatus were measured at 25kHz and 100kHz in Cheju port (Korea). Probability density functions (PDF), i.e., Rayleigh PDF and Rice PDF, were fitted to the distribution of backscattering amplitude from the live swimming crab. The following results were obtained: (1) TS was more dispersed at 100kHz than at 25kHz. (2) The PDFs of the backscattering amplitude agree approximately with Rice PDF at 25kHz and with Rayleigh PDF at 100kHz. (3) The Rice parameter γ tends to decrease with increasing carapace length, carapace width and acoustic frequency. (4) The averaged TS , estimated from PDFs, is about 2dB higher at 25kHz than at 100kHz. (5) Mean values of averaged target strength B, which is normalized with respect to body weight, are -52.5dB at 25kHz, -54.9dB at 100kHz. These values agree approximately with those of bladder fish.