landings were in 1932. Subsequent landings decreased, and the canneries 

 closed in 1947. Meat shortages during and immediately after the 2nd world 

 war created increased demand for clams. Greatest landings of Mercenaria were 

 in 1947. Effects of domestic and industrial pollution are largely to deny 

 major segments of the resource to the industry rather than to affect the 

 resource itself. Larger populations of clams in closed areas are a temptation 

 to poachers and a threat to public health. Storm runoff is a particularly 

 difficult aspect of pollution. Biotoxins such as that caused by dinoflag- 

 ellates are not a major problem to the hard clam industry except indirectly 

 through erosion of consumer confidence in shellfish generally. Fluctuations 

 in hard clam landings have economic causes, related to seasonal demand and 

 competition, as well as to fluctuations in bioliogical production. Areas 

 harvested regularly tend to have poor recruitment, although occasional large 

 sets, which support harvesting for several years, occur infrequently. 

 Hatchery techniques for rearing young or "seed" clams are well developed. 

 Juveniles must be protected from predation if hatchery seed is to contribute 

 to the commercial supply. Smallest clams are most susceptible to predation. 

 Management is difficult because points of landing are numerous, and 

 jurisdiction over the resource and the harvest often is divided among levels 

 of government, as in New York, where towns, counties, State, and several 

 federal agencies share responsibility. Maximum sustainable yields are not 

 known for any hard clam resource. Recreational harvesting is increasing, 

 and the catch is not known. Mechanical harvesting is allowed in some places 

 and under certain conditions, but much of the catch is taken by hand, with 

 tongs, rakes and by treading. The smallest legal sizes, littlenecks, bring 

 the highest price. Regulations primarily relate to minimum size limits, 

 licensing, legal harvesting methods, closure of polluted areas, and sanitary 

 requirements. Buyers must have shippers permits and shipments must be 

 packaged and identified as to source. In dry storage at reduced temp hard 

 clams will live 1 to 3 weeks. Most hard clams are sold in the shell, so 

 storage and waste disposal problems are minimal. Marketing of smaller sizes 

 is not considered a problem. Marketing of largest sizes, "chowder clams", has 

 always been a problem. Prices of all sizes vary seasonally. Markets are 

 influenced by events such as the kepone incident in Virginia. Harvesting 

 pressure has increased in most areas and the resource shows signs of 

 declining. Most states lack adequate information for management, and public 

 attitudes are not sympathetic. Principal needs are: 1) pollution abatement; 

 2) reduction of illegal harvesting; 3) stock assessments; 4) increased 

 aquacultural effort and full use of proven techniques; 5) evaluation and 

 improvement of management regulations; 6) public policy that encourages 

 leasing of marginal or barren grounds for aquaculture; 7) depuration and 

 transplantation of polluted clams; and 8) study of clam population dynamics 

 to develop strategy for stock utilization. - J.L.M. 



1553 



Roberts, B. S., G. E. Henderson, and R. A. Medlyn. 1979. 



The effect of Gymnodinium breve toxin (s) on selected mollusks and crusta- 

 ceans. In Toxic Dinof lagellate Blooms. Dennis L. Taylor and Howard H. 

 Seliger (eds.). Elsevier/North-Holland, New York: 419-424. 



Two groups of clams, Mercenaria campechiensis , were collected locally and 

 exposed to live G. breve cultures or to NH-15. The clam meat was stored 

 frozen in small packages and thav/ed as needed during feeding experiments 

 with adult Callinectes sapidus and Menippe mercenaria. The first group 

 collectively filtered an estimated 2.4 x 10^ cells in 10 days after which 

 toxicity was assayed as 41 mouse units. The second group filtered about 

 3.3 x 1()9 cells in 15 days and toxicity was assayed as 60 mouse units. 

 No tests were made on Mercenaria campechiensis . - J.L.M. 



433 



