Volume backscattering strength of ice krill (Euphausia crystallorophias) in the Amundsen Sea coastal polynya

Abstract

Volume backscattering strength (S_v in dB re 1 m^-1) of ice krill (<em>Euphausia crystallorophias</em>) was observed at two frequencies (38 and 120 kHz) with a calibrated split-beam echosounder system in the Amundsen Sea coastal polynya. The horizontal and vertical scattering layers in the upper 200 m of the water column were known with the existence of predominant ice krill (>95%) in this region. Acoustic identification using a two-frequency dB window between S_v at 38 and S_v at 120 kHz separated echoes originating from dominant ice krill from other zooplankton species. The frequency dependence of ice krill at 38 and 120 kHz was examined and the result presented that ice krill might have different acoustic characteristics from other Southern Ocean zooplankton species including Euphausia superba. This result could be applied to improve the ability of acoustic identification and precise density estimation of ice krill in the high-latitude coastal waters of Antarctica.