essentially an ocean environment. Young clams are completely absent, and 

 the population consists entirely of large clams, blunted with age, uniform 

 in size. Complete absence of young makes it appear that this population 

 originated as a single year class. Productive populations of mixed year 

 classes with continuous recruitment normally occur in the lower estuary. 

 Factors that induce spawning are undoubtedly complex and numerous, but it 

 is believed that temp is of greatest importance. At optimum temp hard clam 

 larvae begin to set as early as 7 days after fertilization, but unfavorable 

 temp may delay setting to as much as 30 days. Better understanding of 

 larval behavior and physiology would have practical advantages for the 

 industry. Part of the difficulty in studying setting behavior is that 

 setting is seldom observed directly. Formation of assemblages or 

 populations of commercial mollusks needs further study. The relationship 

 between food and growth is important, but imperfectly understood. Hard 

 clam differs from oyster in that it can utilize Chlorella and green 

 flagellates even in concentrations that make the water soupy green. Water 

 circulation is important, but only in its capacity to deliver an abundant 

 food supply. Limits of the range of north-south distribution are de- 

 termined by water temp, but the exact effect of temp upon growth within 

 the species range has received little attention. Hard clam growth is slower 

 in higher latitudes. Effects of salinity on growth are poorly known. 

 Experiments by the author have shown that growth is favored by slight 

 dilution of seawater to about 24 to 28°/ 00 . Little is known about oxygen 

 requirements. Hard clams grow better in sand than in mud. Little has been 

 published on the relation between water depth and growth. Hard clams can 

 reestablish themselves in the substratum if disturbed. Young clams are more 

 active than adults. Clams are vulnerable to predators, especially in 

 juvenile and young stages, and their. best defense is a high reproductive 

 potential. Young of predatory species are much more abundant than adults, 

 and they usually are present when clams are young, hence can be highly 

 destructive. No direct evidence exists to show that exploitation has an 

 influence on propagation of a commercial mollusk species. The view that 

 exploitation affects propagation adversely is indirect and tenuous and 

 needs study. Hard clam farms in existence at the time of writing were 

 merely holding grounds, for marketing at times of higher prices. The 

 author did not visualize a bright future for shellfish farming. Much of 

 this review paper deals in general with mollusks without specific reference 

 to species. Examples are drawn mostly from literature on oysters, mussels, 

 and soft clam. This abstract has selected for the most part only specific 

 references to hard clam. Since the time of writing, many existing gaps in 

 knowledge of hard clam biology have been filled, at least partially, 

 although much remains to be done. - J.L.M. 



1840 



Turner, Harry J., Jr. 1955. 



Seventh report on investigations of the shellf isheries of Massachusetts. 

 Mass. Dept. Natural Resources, Div. Mar. Fish: 3-4, 17-20. 



Preliminary studies of feeding of Venus mevcenavia showed that quahaugs will 

 take almost any small particle into the digestive tract, but siliceous diatoms 

 and armored flagellates passed through undigested. Chlorella and related 

 forms, and naked flagellates, were digestible. Artificial propagation of seed 

 shellfishes would benefit the shellfish industry by providing a reliable source 

 of seed. Massachusetts has about 3,000 acres of intertidal and shallow waters, 

 about half of which was suitable for quahaugs. A suggested management plan 

 would be to rotate grounds every 3 yrs , which is the average time required to 

 produce littlenecks. The plan would require seeding of 500 acres/yr. Each 

 acre would support a million quahaugs, and with, low mortality would yield 1,000 

 to 1,500 bu of littlenecks in 3 yrs. Thus, a hatchery would have to produce at 

 least 500 million seed quahaugs/yr. According to available information, an 

 installation of reasonable size could rear this many seed clams to 

 metamorphosis. Techniques based on the work of Loosanoff (1954) abstracted 

 elsewhere in this bibliography, are described. Mortality of natural sets of 

 soft clam may be as great as 99% before legal length of 2 inches is reached. 



511 



