A General Guide for Deriving Abundance Estimates from Hydroacoustic Data








Survey Calculations

The goal of the acoustic surveys described in this web site is primarily to estimate fish abundance.  Fish abundance within the insonified volume can be obtained if we know the backscattering cross-section or target strength of the observed targets.  These abundance estimates can be expanded to whole lakes and populations.  Several steps are necessary, including removing noise and unwanted echoes from invertebrates, identifying the observed targets using sampling, prior knowledge of distributions, and target strength distributions, accounting for volumes not sampled (surface and bottom), and expanding the estimates to a defined survey area.  Each of these steps also includes uncertainties and the combined uncertainty represents the precision in an acoustic estimate of fish abundance.  In this section we will go through these steps and provide a calculator for estimating the total uncertainty in a survey.


Total backscatter

Backscattering cross-section

  • In situ target strength
  •     Single target detection
  •     Density effects
  • Ex situ target strength
  • Theoretical model TS
  • Density

  • Density per unit volume
  • Areal or total density
  • Abundance

  • Simple random sampling analysis
  • Stratified sampling analysis
  • Cluster sampling
  • Geostatistics
  • Species-specific abundance and biomass

    Uncertainty in acoustic surveys