Empirical results on precision - effort relationships for acoustic surveys
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Repeated echo integrator surveys using a rather dense survey grid were performed in areas where the effect of fish migration was assumed to be insignificant. Relative estimates of fish abundance representing different survey grid densities were calculated by using observations along all transects, each second transect, each third transect and so on. The "degree of coverage" of an area was defined as the ratio between "sailed" distance and the square root of the total area covered. Coefficients of variation of the relative estimates were calculated for each degree of coverage. Observations and results for different areas are compared and discussed, and curve fit between the coefficient of variation and the degree of coverage for the observations are presented. Coefficients of variation estimated from the inter-transect variation are compared with the observed ones.