164 MARINE FISHERIES OF NORTH CAROLINA 



He reports clams growing in waters of densities ranging from 1.009 to 

 1.026 with no apparent differences in rates of growth. Loosanoff (1943) 

 reports that natural clam beds occur in brackish water with salinity ranges 

 from 10 to 28 parts per thousand and that clams can tolerate wide fluctua- 

 tions over short periods. 



Following the hurricane of 1933, which caused great damage to the 

 outer banks of North Carolina and ruined the oyster beds in the Harbor 

 Island region, a great abundance of clams appeared in the vicinity. Prior 

 to 1933, clams did not exist in commercial quantities in the northern part 

 of Core Sound from Atlantic to Wainwright Island. The appearance of 

 clams in this area seems to be correlated with the increase in salinity due 

 to the new inlets cut through the banks, particularly Drum Inlet. Galtsoff 

 and Seiwell (1928) report the average salinity for this locality as 23 parts 

 per thousand. In August and September 1948 the salinity in this area was 

 32 parts per thousand. The increased production of clams in 1936 is 

 attributed to the abundance of clams in this region. In recent years these 

 clam beds have been productive and of importance because of their acces- 

 sibility to the marketing centers. 



GROWTH, Hard clams grow more slowly in northern waters than the 

 other economic mollusks. In the New England area, the average size of a 

 clam at the end of the first growing period (i.e., from the fertihzation of 

 the egg to cold weather) is less than a quarter of an inch. About four and 

 one half years are required to produce a clam three inches in length. 

 Kellogg (1903) states that the growth of clams is greatest in the intertidal 

 zones where they are exposed for intervals each day. However, Belding 

 (1912) says that clams which are covered constantly by water grow more, 

 for they are able to feed for longer periods, Belding's experiments show 

 that 14-millimeter clams have the greatest growth rates; that above this 

 size the amount of new shell laid down diminishes with increase in age. 

 Crowded conditions may result in competition for food and space; but 

 often under such conditions clams are forced out of the bottom and 

 exposed to enemies, Belding (1912) found that "sharps" do not result 

 from the planting of "blunts" and concluded that shell growth once re- 

 tarded, as in "blunt" clams, does not readily recover. 



TEMPERATURE, In the coldcr waters, shell growth does not occur during 

 the winter months, Belding (1912) showed that shell growth commences 

 when the water temperature reaches 49° F. (9° C.) and ceases when 

 temperature declines to about 45° F. Loosanoff (1939-a) has confirmed 

 this, showing that hibernation begins soon after the temperature decreases 

 to S to 6° C. (41 to 43° F,). 



ENEMIES, The youngest stages are exposed to more enemies than the 

 adults. Fish, crabs, various snails, and starfish prey upon the young clams 



