Northwest Fisheries Science Center

Display All Information

Document Type: Journal Article
Center: NWFSC
Document ID: 947
Title: The acoustic Properties of Salpa thompsoni
Author: P. H. Wiebe, D. Chu, S. Kaartvedt, W. Melle, E. Ona, P. Batta-Lona
Publication Year: 2010
Journal: ICES Journal of Marine Science
Volume: 67
Issue: 4
Pages: 583-593
Keywords: zooplankton, Salpa thompsoni, acoustic detection, salp target strength, salp material properties, salp in situ images, DWBA salp backscattering model
Abstract: 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 salps 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 thompsonis material properties. Individual aggregates were mostly 45.560.6 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 275 and 276 dB at 38 kHz, with a secondary peak at approximately 265 dB. TS ranged between 285 and 265 dB at 120 and 200 kHz and peaked around 274 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.