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

• Published in: ICES Journal of Marine Science
• Main Author: Jørgensen, Roar
• Format: Article in Journal/Newspaper
• Language: English
• Published: Oxford University Press (OUP) 2003
• Subjects: Ecology; Aquatic Science; Ecology, Evolution, Behavior and Systematics; Oceanography; Barents Sea
• Online Access: http://dx.doi.org/10.1016/s1054-3139(03)00115-2; http://academic.oup.com/icesjms/article-pdf/60/5/1056/29119899/60-5-1056.pdf

Abstract 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 condition factor (assumed higher fat content), which gave the fish additional buoyancy and less need for swimbladder volume. The effect of gonad weight on TS was not significant. Comparisons of measurements made with vertical and tilted transducers demonstrated a small but significant effect of tilt angle on TS.