Sources and magnitude of random errors in Acoustic Fish Abundance Estimates

The uncertainty of an acoustic fish abundance estimate originating from the integrator output is investigated. A series of 8 consecutive echo integrator surveys covering the same area in the Skagerrak are analysed, treating the integrator readings as a time series. The mean integrator output for one survey (160 observations) is estimated with a relative high precision as the standard deviation is found to be about 0.2% of the mean. The mean integrator output varied with survey indicating a real time trend.