Deep-scattering layer, gas-bladder density, and size estimates using a two-frequency acoustic and optical probe

摘要: Estimating the biomass of gas-bladdered organisms in mesopelagic ocean is a simple first step to understanding ecosystem structure. An existing two-frequency (38 and 120 kHz) acoustic optical probe was lowered 950 m estimate number size gas-bladders. In situ target strengths from 38 120 kHz their difference were compared with those gas-bladder resonance-scattering model. Predicted mean equivalent spherical radius varied depth, ranging 2.1 mm (shallow) 0.6 (deep). Density night-time throughout water column highest (0.019 m -3 ) 200–300 depth range. Predictions kHz volume-backscattering strength ( Sv density could explain 88% vessel's at this location (S 40.9, E 166.7). Catch retained by trawls highlighted presence fish similar range but different densities while measurements distribution gas-inclusion siphonophores. Organism behaviour gear selectivity limits validation estimates. Simultaneous verification multifrequency or broadband targets are required verify species, biomass.