in some way they are then subject to predation by the crab Caroinus maenas . 

 Experiments showed that unless protected until at least 2 cm, survival of clams 

 was poor. Estimates of growth and survival were obtained by holding groups of 

 2 00 clams in a wooden frame 61 cm square by 9 cm deep, sunk flush with the 

 beach surface. The top was closed with plastic mesh against predators. 

 Samples of various sizes of clam were planted at 16 sites. Clams were 

 measured at beginning and end of successive growing seasons. Average shell 

 lengths each year, of clams 10 mm when planted, were: 1 yr, 23.2 mm; 2 yrs, 

 35.6 mm; 3 yrs, 47.2 mm; 4 yrs, 58 mm. Mortality was about 12%/yr among 

 clams 9-13 mm at planting, falling to 3% when 17-21 mm at planting. Growth 

 is limited by water temperature. At Conwy, May to September is the growing 

 period. Quahaugs thrive in soft muddy areas unsuitable for other shellfish 

 culture. If the New England grading system were used, clams would reach 

 "littleneck" size about 4 years after planting. A yield of a million clams 

 55-60 mm long from 0.4 ha can be expected (littleneck size is 50-60 mm). 

 This yield would weigh 30 tons. (Abstracter's note: 30 tons is roughly 750 

 bushels = about 750 bu/acre.) - J.L.M. 



1933 



Walne, P. R. 1976. 



Factors affecting the relation between feeding and growth in bivalves. In 

 Harvesting Polluted Waters. 0. Devik (ed.) . Plenum Press, New York: 169-183. 



Experiments on Meraenaria meraenaria in June-September showed that in absence 

 of additional food, some growth took place in natural seawater, but 

 proportion of dry meat expressed as condition index (dry meat/dry shell) 

 declined. When extra food was added, growth was enhanced, and condition 

 index also improved. In 21 days in natural seawater, hard clams grew from 

 shell weight of 36.8 mg to 53.4 mg with no added food, to 92.1 mg with 20 

 cells/ul Tetraselmis , and to 97.1 mg with 100 cells/yl Isochrysis . Percent 

 meat went from 4.7 initially to 3.5, 5 . 8, and 5 . 2, respectively. In filtered 

 seawater shell weight was 41.9 mg with no food, 81.6 mg with Tetraselmis and 

 94.6 mg with Isochrysis ; meanwhile percent meats were 3.2, 4 . 8, and 5.2, 

 respectively. Different species of algae show wide differences in food value. 

 Species used in the laboratory may not be representative of those in natural 

 environment. No good non-living diet has yet been developed. The small 

 particles required are attacked readily by bacteria, which foul the water. 

 Given an adequate diet, too much food leads to waste through production of 

 pseudofeces, low conversion efficiency, and poor growth. Suitable water 

 currents are necessary to stimulate feeding and carry away feces. Increased 

 temp may hasten growth but divert energy from somatic to gonadal growth. 

 Increased temp also appears to hasten shell growth more than meat growth. 

 This may explain the observation that shellfishes at low latitudes tend to be 

 in poorer condition than those at high latitudes. - J.L.M. 



1934 



Walne, P. R., and G. J. Dean. 1967. 



Studies on the introduction of the American clam (Venus (Meraenaria) 

 mercenaria) (L.) into British waters. Internatl. Counc. Explor. Mer, Fish. 

 Improvement Comm. 1967/E.6, 12 p. (mimeo) . 



Breeding stock from Southampton Water was the origin of most animals. Clams 

 have been raised in late winter or early spring to obtain maximum advantage 

 of the summer growing season. Length of conditioning season for 3 successive 

 winters was 2 9 to 52 days. Larvae were reared in polyethylene bins of 75 1 

 capacity at 5,000 to 10,000 per liter. Average results for 3 yrs were: av no 

 of larvae 436,000, 42% metamorphosed, 21 days. Satisfactory results have 

 been obtained by rearing larvae in 12 liter glass tubes at a density of 

 4 0,000 to 60,000 larvae per liter but at this density food must be added 

 continuously. When about 75% of the larvae have metamorphosed spat are 

 transferred to trays with nylon base immersed in seawater. Isochrysis 

 galbana or Tetraselmis suecioa (or a mixture of the two) are added. A closed 

 circulation system is used which holds 4 50 liters. Good growth and survival 

 can be obtained with up to 750,000 to 1,000,000 clams provided algal culture 

 is added continuously to maintain 50 to 100 cells of Isochrysis or 5 to 10 

 cells of Tetraselmis per ul. Growth of competing species of invertebrates 

 can be controlled by a thorough wash with fresh water. Size and numbers per 



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