Target strength measurements of pointhead flounder, Cleisthenes pinetorum, a flatfish without a bladder

Abstract

There are only a few acoustic surveys of the bladderless fish. As is known by all, Atlantic mackerel was surveyed these years by echo-sounder and showed the high target strength at high frequency. In northern Japan, an interesting fish attracted the attention these years which called pointhead flounder, Cleisthenes pinetorum, without a bladder. It is a flatfish but captures prey in the middle water column. And the body shape is not the normal spindle-shaped, but a flat shape, which may cause different acoustic characteristics with Atlantic mackerel. We did the surveys in Funka Bay, northern Japan and keep the samples to the tank to measure the acoustic characteristics of live flounder. The acoustic characteristics of pointhead flounder measured both using the tether method (38, 120 kHz) and free swimming method (120 kHz). During the measurements of free swimming method, we also observed the swimming actions of pointhead flounder and calculated the swimming angle at the same time. We also discussed the characteristics of TS of the swimming angle.There are only a few acoustic surveys of the bladderless fish. As is known by all, Atlantic mackerel was surveyed these years by echo-sounder and showed the high target strength at high frequency. In northern Japan, an interesting fish attracted the attention these years which called pointhead flounder, Cleisthenes pinetorum, without a bladder. It is a flatfish but captures prey in the middle water column. And the body shape is not the normal spindle-shaped, but a flat shape, which may cause different acoustic characteristics with Atlantic mackerel. We did the surveys in Funka Bay, northern Japan and keep the samples to the tank to measure the acoustic characteristics of live flounder. The acoustic characteristics of pointhead flounder measured both using the tether method (38, 120 kHz) and free swimming method (120 kHz). During the measurements of free swimming method, we also observed the swimming actions of pointhead flounder and calculated the swimming angle at the same time. We also discussed the cha...