174 , THE MOLLUSK FISHERIES 



the flat should be chosen in regard to (1) soil; (2) current; (3) tide. 

 A good flat should have a soil which is tenacious and compact, affording' 

 at the same time easy digging. Probably the best soil is a mixture of 

 fine sand and mud in a ratio of one-third mud to two-thirds sand, as this 

 amount of mud gives the right degree of tenacity. 



The growth of a clam depends upon the circulation of water over the 

 flat, as the current carries the food, and, therefore, the more current 

 the more food for the clams. Current also keeps the bed clean, and 

 prevents contamination and disease from spreading among the clams. 

 Then, again, the growth of a clam depends upon the amount of water 

 over the bed ; i.e., length of time covered. The clam can only feed when 

 the tide is over the bed, and thus the feeding time is limited for the 

 higher flats. While experiments have shown that clams grow faster 

 when continually under water than when exposed part of the time, the 

 question of tide is not so great a factor as that of current in regard to 

 clam growth, and can be almost disregarded. 



The best flat for clam planting is a fairly high flat with a good cur- 

 rent over it, as it gives nearly as rapid growth and a much longer period 

 to dig than a flat which is exposed only a short period. This flat must 

 have the right kind of soil, which must not be shifting sand or too soft 

 mud, but a compact, tenacious mixture. 



The Seed Clams. — Nature has provided the means of stocking these 

 farms. The set of clams is usually restricted to certain localities, 

 which, however, vary from time to time, and heavy sets are found in 

 limited areas. These sets run as thick as 2,000 per square foot of 

 surface, occasionally covering an area of 3 acres. From these natural 

 set areas the natural clam flats are partially restocked by the washing- 

 out of the small clams. More often these whole sets are wasted, 

 as the clams, instead of washing on the good flats, are carried to un- 

 productive places and consequently perish. Thus there are areas of 

 heavy set which are of no use to any one, as practically all the clams 

 perish before they become adults. These areas of heavy set occur in 

 nearly every harbor of the coast to a greater or less extent, and are 

 available for nearly every town. 



The problem now is to make use of these large sets, and not allow 

 them to go to waste. It has been shown that these clams when trans- 

 planted will grow much faster, and will not perish; therefore, clam 

 farming offers both the possibility of saving these natural sets and 

 utilizing barren ground. 



Methods of spat collecting have been constantly referred to in con- 

 nection with clam farming, especially by the Rhode Island Fish Com- 

 mission, and the impression has been given that clam farming can 

 never become a success until some practical method of spat collecting 

 has been found. With the soft clam there is no need of any method 

 of spat collecting, as the natural set is more than sufficient for restock- 

 ing the barren flats. All that is necessary is to utilize the enormous 



