41 



continental climates. Meraenaria meraenaria is one of the most important 

 bivalves of the area. It has evolved into 2 species in the northern and ^ 

 southern parts of its range. Among other east coast species M. meraenaria 

 has been introduced on the west coast. Successful introduction was possible 

 because this clam tolerated cold waters. Hard clam requires salinities no 

 less than about half that of seawater (about 18°/°°), hence is confined 

 to the lower part of Chesapeake Bay. Hard clams less than 1 inch long are 

 scarce because the lower Bay is an area of high predation, mostly by blue 

 crabs. Shelly oyster beds provide best habitats for survival, and most 

 hard clams are harvested in such places. Commercial catch in Chesapeake Bay 

 is mostly clams over 10 yrs old. In the Long Island, N.Y. area, recruitment 

 is regular and young clams grow well. In Chesapeake Bay regularity and 

 intensity of hard clam spatfall is not well understood. One- inch clams 

 planted in sandy bottoms suffered heavy mortality from predation. In mesh- 

 lined trays survival was excellent. Planting hard clams on shelled beds 

 has been advocated to increase survival. Oysters and soft clams tolerate 

 lower salinities, hence are less vulnerable to predation. The Maryland hy- 

 draulic escalator clam harvester could be used to bring buried shell to the 

 surface. Most nursery operations appear to get good survival of young clams, 

 but growth is less than in nature. Hard clams are considered prime at sizes 

 small enough for harvesting before growth has become excessively slow. 

 Estuaries and lagoons of the Atlantic coast have extremely wide variations 

 of environmental factors seasonally, thus it seems unlikely that large 

 natural areas can be protected from such variations for efficient maricul- 

 ture. Modification of environments for rearing early stages seems well 

 within reach. Because natural environments are seldom "right" for long, 

 full advantage should be taken of opportunities to manipulate shellfishes 

 into the best habitats according to season and objective. - J.L.M. 



Andrews, Jay D. 1970. 



The mollusc fisheries of Chesapeake Bay (USA). In Proc . Symposium on 

 Mollusca, Pt. Ill (India) : 847-856. 



Hard clam, Meraenaria meraenavia, supports 1 of 3 major mollusk fisheries 

 in the Bay. Most hard clams are taken on the seaside of the eastern shore 

 of Md. and Va . , e.g., the ocean side of the peninsula that forms the 

 eastern boundary of Chesapeake Bay. Within the Bay the species is limited 

 to lower Bay areas in salinities above 15 / oo . In the Bay most of the catch 

 is made with power-operated patent tongs in water 20 feet deep or more. In 

 the Maryland sector of Chincoteague Bay on the seaside of the Eastern Shore 

 hydraulic soft clam dredges are used, and in Virginia more primitive 

 methods still persist: hand tongs, bull rakes, and treading. The prime 

 market is for steamers (for clam bakes) and raw clams to be served on the 

 half shell. Larger clams are used in chowders and soups. Clams are 

 harvested all year, but seasonal variations in demand have led to a 

 complicated system of storage by intensive protected plantings to hold for 

 favorable prices. Only a small part of the east coast clam harvest comes 

 from the Chesapeake area (16% in 1966). Reproduction, predation, and 

 disease are the major biological problems of the Chesapeake shellfish 

 industry. All three species are prolific, but losses are large in the 

 early stages. Summer-breeding oyster and hard clam are less successful in 

 reproduction than the fall-breeding soft clam. Hard clam has a longer 

 spawning season, at minimum temperature of about 20°C. Size of breeding 

 population has not been clearly related to spawning success. Two 

 experimental hard clam hatcheries are operating on the seaside of the 

 eastern shore of Va. Nursery areas or protection are needed to allow clams 

 to grow to predator-resistant size. Bivalve spat are subject to heavy 

 predation, especially in the first week after setting. In lower Chesapeake 

 Bay 2 snails (Urosalpinx ainerea and Eupleura caudata) , blue crab 

 (Callinectes sapidus) , 4 xanthid crabs, and the flatworm Stylochus ellipticus 

 are considered serious predators. Sea stars (Asterias) , conchs (Busy con), and 

 moon snails (Polyniees ) are less abundant and less important as predators. 

 Skates and rays undoubtedly take some bivalves. In the York River small 

 M. meraenavia are always difficult to find. On bottoms worked commercially 

 clams smaller than one inch are scarce. Blue crabs quickly dig and crack 



