BIOLOGY AND NATURAL HISTORY 179 



Maine a close second. The total production from these states amounted to 

 over sixteen and one-half million pounds of edible portions, valued at over 

 one million dollars in 1940 (Table 8). 



TABLE 8 

 Production of Soft Clans, Atdantic Coast States 



* Net edible meats, exclusive of shells. 

 t Includes catch from private areas. 



NATURAL HISTORY 



In the early development the soft-shell clam does not differ markedly 

 from the other economic mollusks. Spawning is believed to be directly 

 correlated with temperature. Belding (1930) reports spawning as occurring 

 at 70° to 74° F., but Nelson (1928) places the spawning temperature at 10° 

 to 12° C. (50° to 54° F.). Loosanoff (1943) finds that spawning begins 

 when water temperatures reach 55° to 60° F. and continues from three to 

 six months. The sexes are separate and fertilization of the egg occurs free 

 of the parent. Following the embryonic development, the free swimming 

 stages extend ten to fourteen days, after which attachment of the larval 

 clam occurs. Kellogg (1900-b) describes the attachment of young clams by 

 means of a byssus to various seaweeds. {Enter omorpha, Ulva), eelgrass 

 (Zostera), stones, and other objects. The byssal thread may be broken at 

 will to allow the small clams to move a short distance to another location. 

 This attachment of the small clams serves as protection against washing 

 ashore during storms; the sand grains and pebbles to which the young are 

 attached function as anchors. 



As the young clams increase in size, they develop the ability to bury 

 themselves. Small clams under two millimeters in length are not able to 

 burrow, while clams between two and eight millimeters can work their way 

 downward sufficiently to cover themselves. Young clams of two or three 



