ACOUSTIC CHARACTERIZATION OF ICE KRILL DISTRIBUTION IN AMUNDSEN SEA POLYNYA, WEST ANTARCTICA AUSTRAL SUMMER 2011/2012

Abstract

A basin-scale acoustic survey was undertaken in the Amundsen Sea polynya during austral summer (January 2011/Feburary 2012) to find distribution of ice krill (Euphausia crystallorophias). Acoustic data (120 kHz, EK60) and environmental data were collected to explore its broad relationship with the bio-physical environment. Simultaneously, target trawls using bongo net were conducted to obtain length-frequency distributions of E. crystallorophias. All acoustic data attributed to E. crystallorophias were compressed to convert MVBS (Mean Volume Backscattering Strength) using virtual echogram technique. The concentrations of E. crystallorophias were compared with environmental variables (sea ice concentration, bathymetry, temperature, salinity, density, flurosecnece and dissolved oxygen). Higher E. crystallorophias concentrations were observed both at the boundary zone between pack ice and coastal polynya and near ice shelf (Getz), while only low concentration was shown near ice shelf (Dotson). The distribution patterns of E. crystallorophias to be significantly correlated with temperature variations among the several environmental factors. E. crystallorophias density was tended to be greater with increasing mean sea temperature in both seasons.