In Situ Measurements of the Acoustic Properties of Antarctic Krill

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

0125629 Chu Antarctic krill is a key species of the Antarctic marine ecosystem and it is a species that is subject to international assessment and management. A variety of techniques have been used to estimate their abundance and/or biomass including biological and acoustical estimations. However, the total abundance/biomass estimated from the two approaches do not agree and both are subject to considerable errors. The purpose of this proposal is to provide a new approach that can be used to reduce the estimated errors resulting from the acoustic measurements. It is well known that the acoustic technique is far more efficient than the conventional survey techniques involving nets, pumps and trawls in studying the temporal and spatial distributions of zooplankton. However, the accurate interpretations of acoustic scattering data require reliable knowledge of the material acoustic properties (sound speed and density contrasts) of live animals. These material properties depend on the spatial and temporal distributions of the oceanographic parameters: temperature and pressure, as well as the animals body structure. For fluid-like weakly scattering marine animals, such as krill, small variations in the sound speed can result in substantial variations in the measured volume scattering strength. The lack of the ability in predicting and/or measuring the variations of the acoustic properties in situ greatly affects and limits our ability to accurately interpret the acoustic data and to obtain reliable abundance and/or biomass estimates. This proposal is intended to address this issue by in situ measurement of the material properties of Antarctic krill and their spatial and temporal variability. These measurements are crucial to the abundance and/or biomass estimates in the Antarctic region. To provide in situ measurements of material acoustic properties, we propose to use the Acoustic Properties Of zooPlankton (APOP), developed at the Woods Hole Oceanographic Institution, in a cruise conducted in the Antarctic region. The APOP system is able to measure the sound speed and density contrasts of marine organisms in situ. From this proposed research, we expect to obtain a temporal and spatial variation of in situ material properties of Antarctic krill. By incorporating in situ material properties of Antarctic krill with acoustic and biological survey data, the confidence in estimates of the abundance and/or biomass of Antarctic krill is expected to be strengthened greatly.