1Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido 041-8611, 2Faculty of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido 041-8611, 3National Research Institute of Fisheries Engineering, Fisheries Research Agency, Kamisu, Ibaraki 314-0408, Japan
Side-aspect target strengths (TS) of Euphausia pacifica (10.9∼19.6 mm in total length [TL], n=44) were measured as a function of the incident angle of the ensonified wave at 120 kHz and 200 kHz. These measurements were compared with the theoretical predictions by the Distorted-Wave Born Approximation-based deformed-cylinder model (DWBA model). The measurements agreed with the predictions. Dorsal-aspect TSs as a function of the incident angle of the ensonified wave were also predicted by taking the curvature of the body in their swimming condition into account. The relationship between the reduced maximum TS (TScm, max) in dorsal aspect by the DWBA model and the total length to wavelength ratio (TL/λ) was expressed by TScm, max=36.5 log TL/λ−91.4.