Comparing acoustic model predictions to in situ backscatter measurements of fish with dual‐chambered swimbladders

Lavnun Mirogrex terraesanctae have a dual‐chambered swimbladder and are the dominant fish species in Lake Kinneret, Israel. Bi‐monthly acoustic assessments are used to monitor lavnun abundance but the relation between the amount of reflected sound and organism morphology is not well described. Predictions from Kirchho.‐ray mode (KRM) backscatter models show a sensitivity of echo amplitude to fish length and fish aspect. Predicted mean KRM target strengths matched maximum in situ target strength measurements of eight tethered fish within 2·5 dB at 120 kHz and within 7 dB at 420 kHz. Tilt and roll of lavnun during tethered measurements increased variance of backscatter measurements. Accurate abundance and length frequency distribution estimates cannot be obtained from in situ acoustic measurements without supplementary net samples.