Growth-rings on the shell of the scallop (Pecten maximus) are laid down annually, in spring, and so can be used to determine the age.
Scallops grow from spring to December, and cease growing in winter. The resumption of growth in the spring is marked by the appearance of the annual growth-ring at the edge of the shell.
The first year's growth is of one of two types. A few scallops have shells which show a large first year's growth, 28 mm or more wide, while the great majority have shells which show a small first year's growth, less than 28 mm wide. These two types probably depend on the two principal spawning periods of the scallop, most of the former arising from the spring spawning and most of the latter from the autumn one.
The growth curve of P. maximus is of a type characteristic of lamellibranch shells. The annual growth is greatest in the first two or three years of life, after which it decreases steadily.
Scallops grow more quickly in shallow water than in deeper water.
Possible causes of the annual cessation of growth are discussed.
A paucity of young scallops was noted in the dredge samples, as previous workers have reported. No reason can be given.