predation. Three principal methods of getting seed are: 1) collect 

 juveniles from natural set; 2) artificial propagation; or 3) collect spat 

 or juveniles by some device. Young hard clams are seldom found in heavy 

 concentrations. Usual bottom samples in R.I. contain 1-20 clams/ft 2 . The 

 only exception was the summer of 1951 in Greenwich Bay when samples as high 

 as 600 Venus /ft 2 were taken, but this was unusual. The best natural source 

 of juveniles seen was in Casco Bay, Me. Hard clams in Me. set in years of 

 high temp; a cold cycle might prevent reproduction. The tidal spat trap is 

 a box which fills and empties with the tide, and a system of check valves 

 to force outgoing water through a sand filter. Larvae are brought into the 

 box by the tide and held by the sand. A diagram is given. Traps were 

 tested at Boothbay Harbor, Me., Wickford, R.I., and other locations. 

 Results depended on location, time, and presence of mature larvae. Over 

 1,000 hard clam larvae/ft 2 of filter have been taken in 4 days. Methods 

 now are needed to hold seed until it is predator-resistant. - J.L.M. 



666 



Glude, John B. 19 55. 



Why blame the clam digger? In Dividends from research. Prog. Fish Cult., 

 April 1955: 94-95. 



Decline of the soft clam, Mya avenaria, fishery in New England is attributed 

 to predation, not overharvesting of the resource, as had commonly been be- 

 lieved. Meraenaria (Venus) mercenaria is not mentioned. - J.L.M. 



667 



Glude, John B. 1955. (Discussion leader). 



Summary of knowledge of Venus. 5th Ann. Conf. on Clam Research, Boothbay 

 Harbor, Me. U.S. Dept. Interior, Fish Wildl. Serv. , p. 75-75. 



We know times of spawning and setting, and seasonal patterns of larval 

 abundance. It has widely fluctuating and highly localized year class strength. 

 Year class strength can be predicted one or two years in advance. We can 

 determine age and growth. Growth rates vary in time and space. It can be 

 transplanted. Seed can be produced by artificial propagation. Seed from 

 natural reproduction is available in large quantities in certain places and 

 times. It can be farmed in certain areas. Mortality in limited areas and 

 under specified conditions is known. Relation between present fishing 

 intensity and probable yield is known for Greenwich Bay. Predation is most 

 important on Venus under one inch long. Green crabs and horseshoe crabs can 

 be excluded from intertidal areas by fencing. No mass mortalities 

 attributable to parasites or diseases have been observed. We think clams do 

 not remain in place after setting, but are redistributed by hydrographic 

 conditions or by movement. At present levels of abundance there is no 

 relation between number of adults and number of progeny that reach commercial 

 size from variations in mortality. Length of larval stage is related to 

 temperature. Currents are important in determining distribution. Further 

 exploration would disclose additional sources of natural seed. Mortality of 

 Venus above 20 mm is low in Rhode Island. We do not know the food, extent of 

 movement of young and adults, or what determines distribution, behavior, 

 and survival of larvae. We do not know enough about the effects of 

 environment on survival from the time they set until they reach the stage 

 at which year class strength can be predicted, or enough about causes of 

 variations in growth. We do not know if experimental procedures for 

 artificial propagation can be applied to commercial scale seed production. 

 We do not know the effect of the fishery on clams not harvested, the 

 mechanics of productivity, or how to estimate and control predation on 

 subtidal Venus populations, or what is the minimum population level at which 

 commercial fishing is no longer profitable. - J.L.M. 



668 



Glude, John B. 



Clam and Chesapeake oyster investigations 1948-57. U.S. Fish Wildl. Serv. 

 Could not locate. Search terminated. - J.L.M. 



186 



