92 THE SCALLOP FISHERY 



Waters of high temperature usually show more rapid growth, prob- 

 ably due to (1) the earlier start in the spring and longer season, (2) 

 more rapid growth throughout the summer months from an increased 

 food supply. Diatoms multiply more rapidly in warm waters and the 

 food supply is consequently greater. The effect of temperature can be 

 seen by comparing the scallops of Cape Cod and Buzzard's Bay. The 

 former do not attain the size of the latter, which are the largest scallops 

 produced in the Commonwealth. The same comparison holds true 

 between Rhode Island and Massachusetts, as in the warmer waters of 

 Narragansett Bay the scallops develop more rapidly. While in both 

 cases other natural conditions play an important part, it is only fair 

 to assume that temperature is a most important factor. 



(e) Growth and Salinity. The oyster is extremely sensitive to 

 changes in the salinity of the water, both in regard to spawning and 

 growth. The growth of the scallop, on the other hand, is not materially 

 affected by these changes. A sudden decrease in salinity, as after a 

 severe rain, often kills young scallop larvse, and transferring scallops 

 from water of one density to another during the breeding season has 

 been found to check the spawning. 



Scallops are found in waters ranging in density from 1.010 to 1.027, 

 i.e., an equal mixture of salt and fresh, as in mouths of rivers, to 

 extreme salinity. Rough experiments have demonstrated that scallops 

 live and grow equally well between these limits, and that any differences 

 in growth are due to other conditions. 



(/) Depth of Water. The question of the most favorable depth for 

 growth is of importance to the scallop planter. In nature scallops are 

 found at any depth, from flats exposed at low tide to 60 feet, although 

 the usual limits are less than 25 feet. In too shallow water severe 

 winters destroy the sets, so the scallop should be deep enough to escape 

 the ice. As shown by the channel v. eel-grass (shallow water) scallop, 

 the greater growth occurs in the deep waters; but, as has been stated, 

 this is essentially due to the better circulation in the channel. 



Scallops were suspended in wire baskets from the raft in the Powder 

 Hole at different depths during the summer of 1906. The water was 

 20 feet deep. Four baskets, each containing 100 "seed" scallops 

 about 20 millimeters in size, were suspended for seventy-six days at 

 6, 7, 8 and 9Vfe feet from surface. When measured a regular decrease 

 of about one millimeter per foot was found, the 6-foot basket evidencing 

 the greatest gain, and the rest less in definite order, ending with 9V2- 

 foot basket. These figures indicate that the best depth for this particular 

 locality was about 5 feet from the surface. Similar experiments with 

 older scallops gave negative results. 



Artificial Growth. The greater part of the growth experiments on 

 the scallop were conducted under the artificial conditions that would be 

 employed in scallop culture. In order to record the rate of growth 



