© 2003 by ICES/CIEM International Council for the Exploration of the Sea/Conseil International pour l'Exploration de la Mer
The effects of swimbladder size, condition and gonads on the acoustic target strength of mature capelin
Norwegian College of Fishery Science, University of Tromsø N-9037 Tromsø, Norway
*R. Jørgensen; tel: +47 77 646084; fax: +47 77 646020. e-mail: roarj{at}nfh.uit.no.
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.
Keywords: cage experiment, swimbladder, capelin, tilt angle, condition, maturation
Received 28 December 2002; accepted 2 April 2003.
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