Over five million spat of the king scallop, Pecten maximus (L.) were collected accidentally in the North Water of Mulroy Bay in County Donegal, Ireland in the summer of 1979. This large natural settlement, by far the greatest number obtained at the time in any European trial, led to research investigations in 1980 and 1981 to support the development of this site as a scallop spat collection center. A combination of gonad monitoring, plankton sampling, spat settlement and spat collection trials were used to develop a technique for predicting the date of the scallop spatfall to maximize the yield of scallop spat. A technique for forecasting the date of peak spatfall involving installation of spat collectors when the mean shell length of scallop larvae was 180 μm and 50% of the larval cohort exceeded this size was developed. Unlike other sites studied, peak spat collection occurred at 4 m beneath the water surface. Since its development, this technique for prediction of the date of the peak collection has been used commercially, and for illustrative purposes data from 2002 have been provided. The development and application of this forecasting technique has assisted in the collection of millions of scallop spat for ongrowing trials by the scallop culture industry.