Abstract:

Acoustic surveys are commonly used to estimate the biomass of Antarctic krill (Euphausia superba). Accurate biomass estimates depend upon knowing the acoustic backscattering properties of the animals. A generic scattering model for individual E. superba was developed and tested against laboratory measurements. The model was based on morphometric measurements of live krill and employed a simplified form of the distorted wave Born approximation (DWBA) method. The model included the effects of animal length and orientation. Backscattering measurements of live individual Antarctic krill were made at 120 kHz as part of the August, 1995 Bioacoustical Oceanography Workshop in Santa Cruz, CA, jointly sponsored by the National Science Foundation and the Office of Naval Research. Animals were suspended one by one in an acoustic beam, with substantial freedom to move and thus with more or less random orientation. One-thousand echoes were collected per animal, and target strength was calculated for each echo. Behavior was recorded on video. The video data were used to estimate three-dimensional orientation for five of the animals, thus giving their target strengths as functions of orientation. The measurements supported the major features of the scattering model.