88 THE SCALLOP FISHERY 



(a) Growth in Eespect to Current. The most important factor in 

 shellfish growth is a good current of water. The use of the word cur- 

 rent does not mean necessarily a rapid stream or an exceedingly swift 

 flow, but a good circulation of water over the bed. 



The chief office of the current is as a food carrier. The scallop ob- 

 tains its nourishment from microscopic plants, called diatoms, which are 

 found throughout the water. The amount of this food is approximately 

 uniform, and the scallops situated in a current naturally receive more 

 food than those in still water. With mollusks the growth is directly 

 proportionate to the amount of food, and the scallop receiving the most 

 food increases in size most rapidly. A homely comparison can be made 

 by likening the scallop in the current to the man seated at a moving 

 lunch counter, who is able to continually obtain a new supply of food, 

 while his neighbor at the stationary table (the scallop in the still water) 

 is limited to the food within reach. For all practical purposes current 

 means food, and within limits the increase in current indicates the 

 increase in the amount of food, thus furnishing an index for the rate 

 of growth. Theoretically, other factors enter into the problem, such 

 as (1) variations in the amount of food in different localities; (2) the 

 feeding capacity of the scallop, since beyond a certain maximum value 

 an increase in current means no increase in the amount of assimilated 

 food; (3) the freedom of the water from contamination and silt, which 

 impedes the feeding powers of the animal. The shellfish culturist can 

 take the current as his guide for planting, and follow the rule that, 

 as long as the flow of water does not harm the planted shellfish in other 

 ways, the swifter current gives the faster growth. 



Current not only brings food to the scallop but also furnishes the 

 lime in solution which is utilized in building the shell, a process as 

 essential in the growth of the scallop as the nourishment of the soft 

 parts by the food in the water. The amount of lime in solution varies 

 in different waters, but this difference is largely obviated by the changes 

 in the current. As an example, a scallop will grow no faster in water 

 rich in lime which is comparatively stagnant than it will in water rela- 

 tively much poorer where there is a stronger current. 



The third office of the current is a purely sanitary one. It sweeps 

 away the decaying vegetable matter so destructive to scallops situated 

 in thick eel grass, and all other poisonous debris which would otherwise 

 kill the scallops by contamination, or at all events would check their 

 growth. 



The relationship of current to growth has been experimentally shown 

 in several ways, all of which demonstrate that in the case of the scallop 

 current is the main essential for rapid development. The following 

 observations and experiments are cited as confirmatory evidence : 



(1) Eel-grass v. Channel Scallops. In observing the catch from 

 the scallop beds, it was recorded that the larger scallops always came 



