Scallops spawn in spring at 7-12 °C. The density of settlement depends on the concentration of larvae in the water column; this is closely monitored to predict both the timing and intensity of settlement. Spat collectors are suspended in the water column when monitoring programmes determine that >50 percent of larvae exceed 200 µm in length. Two types of spat collector are used:
Plastic monofilament packed 'onion' bags attached 10 to a rope of 5 m length.
Conical plates of perforated plastic that are strung together in batches, usually of 25, by rope to form a string of 2.5 m length, which is then covered by fine mesh.