densities. Tong operators take from 1000 to 3000 clams per day on areas of 

 moderate densities, and up to 7500- clams per day in areas of high abundance. 

 Tong operators state that they cannot make a living in areas of low 

 densities. Because the clam resource is geographically concentrated, it is 

 vulnerable to overfishing. Fishery scientists and managers must monitor the 

 resource closely to detect signs that there is danger of overfishing, 

 including: increased natural mortality, reduction in recruitment, or decrease 

 in catch per unit effort. The clam resource is vulnerable because recruitment 

 is poor over most of the bay. Good recruitment, indicated by high abundance, 

 low average length, and high percentages of littlenecks and cherrystones are 

 limited to the aforementioned six areas. Clams were planted experimentally 

 in the lower James and York Rivers where most of the fishery operates. 

 Growth rates in these areas were slow relative to growth in higher salinity 

 waters. Littleneck size is attained in about 2 1/2 years, and cherrystone 

 size in 4 1/2 years by clams in the Hampton Flats; however, it takes 4 and 

 8 years respectively for clams in similar areas in lower York River. Chowder 

 clams range from 8 to 20 years old. When high rainfall depresses salinity 

 below normal, growth is slowed and mortality increases. The Virginia hard 

 clam fishery probably has operated near MSY in recent years. Catch per unit 

 effort, measured as weight per license, decreased when effort increased. 

 (Abstracter's note: This is inevitable, but not necessarily a sign of over- 

 harvesting.) It was recommended that effective effort be stabilized until 

 the resource can be analyzed in detail and goals of management are specified. 

 The following options for hard clam management would allow increased landings 

 without being detrimental to stocks presently fished: 1) permit commercial 

 dredging for clams in Chesapeake Bay in waters greater than 18 feet (MLW) 

 because it is not economically feasible to clam these low density areas with 

 tongs; 2) encourage lessees of MSX-affected oyster beds with good hard clam 

 resources to enter the fishery; 3) determine if private hard clam mariculture 

 is a feasible commercial operation. Extension of the open season in lower 

 James River would increase landings , but would affect the presently 

 available stock. Harvesting costs could be reduced by allowing use of more 

 efficient gear, but this would displace men and gear now in the fishery or 

 reduce the stock. An adequate statistical program should be implemented as 

 soon as possible. Management program should be re-evaluated at least 

 annually on the basis of vital statistics obtained and socio-economic 

 conditions in the fishery. Clam farming was investigated in the York River. 

 Plastic netting (1/4 inch mesh) did not protect seed clams from predators. 

 Survival of seed was higher on gravel bottoms at 5 feet (MLW) than on 

 natural bottoms, but gravel bottoms less than 1 foot (MLW) were not effective 

 protection. Hatchery reared clams grew at the same rate as wild clams. 

 Seldom do more than 10% of small clams (1-3 mm) survive for one year and 

 often none survive. In one test plot (5 feet, MLW) survival of larger seed 

 (4-8 mm) ranged from 33-38%. In one test plot no large seed survived. The 

 risk of clam farming is high, so 1/4-1/2 acre plantings in 10-15 feet (MLW) 

 should be tested. Seed should be at least 5 mm. Further clam farming 

 research should be conducted emphasizing clams 5-10 mm or larger planted at 

 depths of 10-15 feet or greater. - D.L. 



802 



Haven, Dexter S.,and Reinaldo Morales-Alamo. 1966. 



Aspects of biodeposition by oysters and other invertebrate filter feeders. 

 Limnol. Oceanogr. 11(4): 487-498. 



803 



Haven, D. S., W. J. Hargis, Jr., J. G. Loesch.and J. P. Whitcomb. 1977. 



The effect of tropical storm Agnes on oysters, hard clams, soft clams, and 



oyster drills in Virginia. In Symposium held May 6-7, 1974 at College 



Park, Maryland. Chesapeake Research Consortium, Inc. CRC Pub. 54. Johns 

 Hopkins Univ. Press, Baltimore: 488-508. 



High mortality of hard clams (Meraenaria meroenaria) held in leased areas 

 in the York and Poquoson Rivers probably resulted from stress of moving and 

 marginal salinities. Light mortality of undetermined magnitude occurred 

 in the York River in very shallow water along shore from the mouth to about 

 19.3 km up-river. Elsewhere, mortalities were about normal. - J.L.M. 



223 



