Quantitative Estimates of Euphausiid Biomass Determined by High-frequency Acoustics

AbstractEcho sounders operated at high acoustic frequencies (∽50–200 kHz) have been successful in recording layers and patches of euphausiids in the more productive areas of the world's oceans. Qualitative records of scattering from the euphausiids provide a mechanism for locating the organisms and directing net-sampling operations. Quantitative scattering measurements can provide biomass estimates. Such quantitative measurements can be made at sea and, therefore, provide a real-time method for studying the vertical distribution and patchiness of the euphausiids. Problems with the acoustical assessment of euphausiids include variations in euphausiid target-strength measurements, the presence of larger scatterers (e.g., fishes) obscuring the euphausiid scattering, and poor resolution when euphausiid densities are low. Continued net sampling of the scatterers is still considered necessary to confirm the identity and size of the recorded targets.