Abstract
An enclosure was designed for experiments estimating the target strength (TS) of the common jellyfish (Aurelia aurita) in the Black Sea. A BioSonics echosounder (Model 102) equipped with 120 and 200 kHz dual-beam transducers was used for the measurements. The average acoustic cross-section for each size class was used in functional regression equations to relate the mean TS (dB) of jellyfish to its disc diameter d (cm) and wet weight W (g). These were found to be as follows: TS=14.72 log d−74.63 and TS=5.71 log W−69.41 at 120 kHz; TS=39.65 log d−104.38 and TS=14.53 log W−88.07 at 200 kHz. The TS values were found to fluctuate periodically with time. The results showed a variation of −54 to −67 dB at 120 kHz for 15.5 cm diameter individuals, with a period of 7.5 to 10 sec; and a variation of −58 to −68 dB for 11.5 cm individuals at 200 kHz, with a period of 6 to 12.5 sec.
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