76 THE SCALLOP FISHERY 



circulation of water or current are the two external factors in the devel- 

 opment of the scallop. 



Growth of Scallop compared with Other Economic Bivalve Mollusks. 

 The limited life and active habits of the scallop require a quick 

 maturity and light shell, which make its growth the most rapid of the 

 economic bivalves. Arranging these mollusks in order of rapidity of 

 growth, scallop, clam, sea clam, oyster and quahaug, we find that they 

 are likewise placed in respect to the weight of their shells, the lightest 

 shell corresponding to the fastest growth. From this we can formulate 

 the general rule that the growth of any shellfish is directly propor- 

 tional to the weight of the shell, which not only seems to hold true for 

 the different species, but is applicable to varieties of the same species; 

 i.e., a thick-shelled clam grows more slowly than a thin " paper " shell 

 variety. 



Variations in Growth. Many variations are found in the growth of 

 scallops. In no two localities is the size identically the same, as can 

 be seen by comparing Buzzard's Bay, Cape Cod and Island scallops. 

 This variation may be called sectional, and can be attributed to the 

 difference in environment, which also applies to local conditions. There 

 is also variation in the sets, the average of one year differing from the 

 succeeding or preceding years. The size of a scallop is due to two main 

 factors: (1) its time of birth, either at the beginning or end of 

 the two months' spawning season; (2) the conditions under which it 

 lives, whether favorable or unfavorable for rapid growth. Primarily 

 the environment and secondarily the time of the set determine in a 

 great measure the life of this mollusk. There is another type, indi- 

 vidual variation, which is important to consider in presenting the results 

 of the growth experiments, as it proves that correct results can only be 

 satisfactorily obtained by records of large numbers of scallops. Risser 

 (2) remarks on the remarkable uniformity of the individuals of the 

 set in Narragansett Bay. No such uniformity has been found under 

 the more diverse conditions in Massachusetts waters, and in individuals 

 of the same set, especially in the young scallop, variations as great as 

 from 1/2 inch to 2^2 inches have been found at the same time and place. 

 Between these extremes all grades can be found converging toward the 

 average. Even when scallops of the same size are confined in pens 

 their growth varies, a fact that can only be attributed to the individual 

 traits of the animal. 



Growing Months. Man passes through four arbitrary periods in 

 life, childhood, youth, manhood and old age, attaining his actual stature 

 during the first two, and only adding more flesh as the years pass. 

 The scallop, on the other hand, continues to increase in size during the 

 adult period, and in fact up to the time of its death has not lost the 

 power of growth, although the shell formation in the old scallops is 

 somewhat slower than in the younger specimens. But the scallop only 



