The acoustic properties of Salpa thompsoni

• Published in: ICES Journal of Marine Science
• Main Authors: Wiebe, Peter H., Chu, Dezhang, Kaartvedt, Stein, Hundt, Anna, Melle, Webjørn, Ona, Egil, Batta-Lona, Paola G.
• Other Authors: Biological and Environmental Sciences and Engineering (BESE) Division, Marine Science Program, Biology Department, Woods Hole Oceanographic Institution, Mail Stop 33, Woods Hole, MA 02543, United States, NOAA, NMFS/NWFSC, FRAM, 2725 Montlake Boulevar East, Seattle, WA 98112, United States, Department of Biology, University of Oslo, PO Box 1066, Blindern, N-0316 Oslo, Norway, Department of Biology, University of Bergen, PO Box 7800, 5020 Bergen, Norway, Institute of Marine Research, PO Box 1870, Nordnes, 5817 Bergen, Norway, University of Connecticut-Avery Point, 1080 Shennecossett Road, Groton, CT 06340, United States
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Oxford University Press (OUP) 2009
• Subjects: Acoustic detection; DWBA salp backscattering model; Salp in situ images; Salp material properties; Salp target strength; Salpa thompsoni; Zooplankton; Antarc*; Antarctic; Antarctic Krill
• Online Access: http://hdl.handle.net/10754/561545; https://doi.org/10.1093/icesjms/fsp263

Aggregations of the salp Salpa thompsoni were encountered during the Antarctic krill and ecosystem-studies cruise on the RV "G.O. Sars" from 19 February to 27 March 2008. The salp's in situ target strength (TS), size, number of individuals in aggregate chains, and chain angle of orientation were determined. Shipboard measurements were made of Salpa thompsoni's material properties. Individual aggregates were mostly 45.5-60.6 mm in mean length; relatively rare solitaries were ∼100 mm. Chains ranged from 3 to at least 121 individuals, and in surface waters (<20 m), they showed no preferred angle of orientation. Sound-speed contrast (h) ranged from 1.0060 to 1.0201 and density contrast (g) estimates between 1.0000 and 1.0039. The in situ TS distributions peaked between-75 and - 76 dB at 38 kHz, with a secondary peak at approximately - 65 dB. TS ranged between-85 and - 65 dB at 120 and 200 kHz and peaked around-74 dB. The measured in situ TS of salps reasonably matched the theoretical scattering-model predictions based on multi-individual chains. The backscattering from aggregate salps gives rise to TS values that can be similar to krill and other zooplankton with higher density and sound-speed contrasts. © 2009 International Council for the Exploration of the Sea.