The bay scallop, Argopecten irradians, spawns for the first time when fully mature, at about one year of age. Because the average life span of the bay scallop is a short 20 to 26 months, individuals rarely spawn more than once in their lifetime. Spawning occurs late in July, when water temperature have warmed above 20 C and food is abundant. The release of eggs and sperm into the water by several mature scallops stimulates "mass spawning" by most mature scallops in the area.
After a free-swimming larval period, generally lasting one to two-and-a-half weeks, the juveniles, called "spat", begin to search for an appropriate settling substrate on which to attach. The most suitable site is eelgrass, but in many New England estuaries, poor water quality has led to the demise of eelgrass beds, leaving a limited amount of appropriate substrate for settling.
Once a spat reaches a length of 20 to 30 millimeters, it detaches from the substrate and drops to the bottom, The adult bat scallop normally rests on its right valve - the right side of its shell - on the bottom, with its valves slightly agape. It is a filter feeder, and feeds primarily on benthic diatoms and bacteria, but may choose other microorganisms as well.
Unlike other shellfish, scallops are active swimmers. They swim by pulsing water in and out of their mantle cavity, commonly referred to as "clapping". In this way, they are quite able to effectively travel short distances to escape predation or unfavorable environmental conditions.
In the winter, growth slows drastically, and the bay scallop hibernates on the bottom of the estuary. Once water temperatures, begin to warm in the spring, the scallop begins to actively feed. And those scallops that hatched the previous summer will have reached maturity and will spawn.