SummaryErrors in estimates of year class strength and mortality among 0‐group plaice can result from migrations. In order to reliably determine the number present, tidal flats and channels in a large and clearly delimited Wadden Sea area (715 km2) were sampled simultaneously using different fishing methods (by‐catch, beam trawls, pushnets, and fyke nets). The numbers of 0‐group plaice calculated for each depth stratum reflected changes in the distribution patterns during the complete diurnal cycle and during the course of the season and proved to be most reliable for estimating the total number in the whole area. In contrast to this, the traditional way of calculating population size by multiplying the arithmetic mean of simultaneous catches resulted in very different numbers which would entail an overestimation of mort