The effects of swimbladder size, condition and gonads on the acoustic target strength of mature capelin

Pre- and post-spawning capelin from the Barents Sea stock were observed in a net pen with a calibrated 38 kHz scientific split-beam echosounder. The transducer was positioned vertically or tilted. The acoustic target strength (TS) of capelin depended on swimbladder length. In female capelin within 15.5–18.0 cm length the logarithm of weight was significantly negatively related to TS. The negative effect of weight on TS could be due to a higher...