Optimum size of sampling unit for estimating the density of marine populations
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Data from several trawling experiments and from some scallop dredge surveys indicate that, within limits, a srnaller sampling unit can be more effective than a larger unit for marine abundance surveys. Taking into account survey costs and sampling variability, the unit size is found which produces the most precise density estimate given a fixed amount of survey resources or, if a certain level of precision is required, the size of sampling unit which minimizes the total cost of the survey. As an illustration, the optimum sampling unit sizes are derived for surveys of some fish populations and for a scallop stock on Georges Bank.