that the subspecies may be of hybrid origin. Subspecies M. m. notata is not 

 valid. M. mercenaria has a smoothish, glossy area on the center outer surface 

 of the valves. Interiors of valves are white, commonly with purple stains. 

 The lunule is 3/4 as wide as long. The species will remain tightly closed 

 out of water up to 2 weeks, especially if kept cool. M. campeehiensis lacks 

 the smooth area on the outer surface of the valves, has persistent raised 

 growth ridges, and more obese shells. Valve interiors have no purple stains, 

 and the lunule is about as wide as long. This species, even under 

 refrigeration, will gape, lose its shell liquor, and spoil in a few days. 

 Reciprocal Fi hybrids between the two species are fertile and the 4 types of 

 F2 hybrid have been reared in the laboratory. Studies of chromosomes of 

 species and hybrids at meiosis and mitosis show that chromosomal behavior of 

 hybrids is normal. - J.L.M. 



1281 



Menzel, R. W. 1970. 



The species and distribution of quahog clams Mercenaria. Proc . Natl. Shellf. 

 Assn. 60: 8 (abstract). 



Northern quahog (Mercenaria mercenaria) and southern quahog CM. campeehiensis) 

 with several subspecies occur along the Atlantic coast of North America. 

 Northern ranges from Canada to Florida and the northern Gulf of Mexico, the 

 southern from New Jersey to Florida, the Gulf of Mexico, and is reported 

 from the West Indies. Northern is confined to inshore waters of bays, in- 

 lets and estuaries, except specimens taken offshore on the northwest coast 

 of Florida. Southern occurs only offshore in the northern part of its range, 

 although one was seen from the mouth of Chesapeake Bay, but occurs inshore 

 south of Cape Canaveral, Florida and in both habitats in the Gulf of Mexico. 

 M. mercenaria notata has no validity based on breeding studies and occurrence 

 of the subspecific trait in northern or southern forms. Museum specimens 

 labelled M. mercenaria alba seem to be bleached M. mercenaria. The northern 

 species is mostly represented by M. mercenaria texana below Cape Canaveral 

 and in the Gulf of Mexico. Northern and southern species hybridize readily 

 in the laboratory and F2 hybrids have been reared. Shell morphology of about 

 3/4 of the F2S is very similar to the subspecies M. mercenaria texana and 

 it suggests this subspecies is a naturally occurring hybrid between the two 

 forms. - J.L.M. 



1282 



Menzel, R. W. 1971. 



Possibilities of molluscan cultivation in the Caribbean. In Symp. on 

 Investig. and Resources of the Caribbean Sea and Adjacent Regions. FAO 

 Fish. Rept. 71.2(4.27): 183-200. 



The commercial quahog fishery in the U.S. is based largely on M. mercenaria 

 and on small clams 50-75 mm long. Large clams are used in chowders, but 

 must compete with more efficiently harvested and abundant Spisula solidissima 

 and Arctica islandica. The relatively small fishery for M. campeehiensis is 

 related to gaping and spoilage soon after it is removed from the water, but 

 also because some areas where it occurs in abundance are polluted, lack of 

 fishery knowledge by local fishermen, lack of markets, and competition from 

 well established and more profitable fisheries for shrimps, crabs, spiny 

 lobster, and mullets. Northern quahogs 10-25 mm long were planted at various 

 concentrations in fenced plots of 125 to 250 m 2 . Mortality usually was less 

 than 10%. Unprotected control plantings had 100% mortality, usually within 

 2 weeks, from crab and gastropod (Busycon) predation. On protected grounds, 

 over 250 clams per m2 would reach market size for half -shell trade in 

 slightly over a year. Observations on laboratory-spawned northern and 

 southern quahog and their Fi and F2 hybrids showed that all showed greatest 

 shell growth in spring and fall. Northern species grew better in winter 

 than southern. In summer, shell growth in northern quahog slowed, but 



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