The major restriction to expansion of scallop culture and scallop fishery enhancement in Europe is a reliable source of scallop spat. In Ireland, production of spat from the natural settlement in Mulroy Bay has exhibited considerable variation over the last 25 years. In this study data available on king scallop spawnings have been reviewed with the objective of understanding why in some years spat are abundant and in others scarce. Similar spawning periods of king scallops, Pecten maximus in two locations 10 km apart, supported the use of scallops from the Broad Water for gonad monitoring rather than from the North Water spat production site where scallop dredging is legally prohibited. Using weekly determination of gonad index, gonad weight and relative gonad height, five partial spawnings were recorded between April to August in 1 year, with scallops capable of spawning 1 week and re-maturing to a pre-spawning level the following week. Sampling frequency significantly influenced the number and size of spawnings recorded, date of the spawning and duration of the spawning event. These results have major implications for data collected using sampling intervals greater than 1 week and purporting to represent the reproductive cycle of this scallop. Based on weekly monitoring of scallop gonads during summer months between 1993 to 2004 there was no significant correlation between intensity of the scallop spatfall and size of the gonad prior to spawning, magnitude of spawning event, date of spawning period within June and July and duration of the spawning event.