Sound scattering by the gelatinous zooplankters Aequorea victoria and Pleurobrachia bachei

Target strengths were determined for individual Aequorea victoria and Pleurobrachia bachei using separate 200, 420 and 1,000 kHz transducers in an enclosure deployed off the dock of the Friday Harbor Laboratories in northern Puget Sound, Washington, USA. The target strength for Aequorea, when averaged over all animal sizes and all three trnasducer frequencies, was −72.6 dB. The target strength for Pleurobrachia was −75.9 dB when similarly averaged. Average reduced target strengths for Aequorea and Pleurobrachia were −43.3 and −33.1 dB, respectively. Differences in the sound scattering contrasts for Pleurobrachia and Aequorea are proposed to explain the larger reduced target strength of Pleurobrachia, relative to that of Aequorea. sound scattering model was developed to predict the backscattering cross-section of Aequorea. The model takes into account expected variations in target strength due to changes in shape of the jellyfish as it propels itself through the water. The scattering model was tuned specifically for Aequorea in the present study, but has a general formulation that is widely applicable to any medusa-shaped gelatinous zooplankter.