regenerated large numbers of ovocytes rapidly, which slowly increased in 

 size in winter and' spring. Roosevelt Inlet clams developed slowly in size 

 and number of ova for a long period. Normal spawning temps in Del. were 

 25-27°C. Henlopen clams developed similarly to Long Island Sd. clams, but 

 the timetable was about a month earlier (June-Sept vs July-Aug) . Roosevelt 

 In. clams showed a pattern different from L.I.S. and N.C. In general, 

 gonadal developmental patterns in Delaware were intermediate between L.I.S. 

 and N.C. Environmental factors were credited with producing subtle 

 differences in reproductive physiology between the 2 localities in Delaware 

 Bay. Hard clams retain a relatively high proportion of glycogen or condition 

 index even after spawning. This allows immediate gonadal redevelopment in 

 fall. - J.L.M. 



963 



Keck, Richard, Don Maurer, and Robert Malouf. 1974. 



Factors influencing the setting behavior of larval hard clams, Mercenaria 

 mercenaria. Proc. Natl. Shellf. Assn. 64: 59-67. 



The setting preference of hard clam larvae was studied in the laboratory in 

 reference to substratum's particle size, chemical composition, and treatment 

 with pheromones. Larvae preferred setting in sand over setting in mud, and 

 in sediment treated with clam liquor rather than untreated sediment. There 

 was no statistically significant association between setting and sediment 

 size other than the preference for sand over mud. - D.L. 



964 



Keck, Richard, Les Watling, and Don Maurer. 1972. 



Survey of Delaware's hard clam resources - Delaware Bay. 1971-1972 Ann. 

 Rept. to Natl. Mar, Fish. Serv., 103 p. 



Covers Delaware waters of Delaware Bay. Hard clam ranges from mouth of Bay 

 to Woodland Beach, Del., about 38 miles up, optimum development is up to 

 about 20 miles from Bay mouth. Only 2 areas in 336 dredge samples yielded 

 more than 6 bu/hr, a marginal commercial density. Clam sizes appeared to be 

 less at lower salinities. In 375 Petersen grab samples only 10 juvenile hard 

 clams were taken. Modal size of all clams was 11.0 to 11.9 cm. No 

 significant correlation was observed between predator abundance and density 

 of clams, but importance of predation on juveniles was noted. Spawning was 

 from June through Sept. Gametogenic activity was low in winter and 

 accelerated in March. Many clams were ripe in April and May. Glycogen 

 content was higher in fall, winter and spring than in summer. In the 

 intertidal area glycogen levels varied much more than in subtidal zone. 

 Laboratory studies showed that higher sets were obtained in sand than in mud 

 and survival was better in sand. Setting was enhanced by treating sediment 

 with clam liquor. It was concluded that hard clam resources in Delaware 

 were not at commercial levels in most places. Small populations were 

 explained by loss of larvae from tidal flushing, unstable bottoms, low 

 nutrient values for phytoplankton, extensive predation, overharvesting, and 

 unknown effects of trace metals. - from authors' summary - J.L.M. 



965 



Keck, Richard, Don Maurer, William Daisey, and Lee Sterling. 1973. 



Hard clam. In Marine Invertebrate Resources. Ann. Rept. 1972-1973. 

 Submitted to Dept. Nat. Resources and Envir. Control Field Sta. , College 

 of Marine Stud., Univ. Delaware, Lewes, Del.: 17-32. 



Most commercial production of hard clam in Delaware comes from Indian 

 River and Rehoboth Bays. Density of clams in these bays was moderate 

 and had decreased since the 1967 study. Seed clams were reared in the 

 laboratory and held until they reached about 1 mm. They were then 

 transplanted to two locations in Rehoboth Bay. Half were protected 

 from predators with aggregate made by crushing surf clam shells, half 

 were unprotected. Approximately a year later about 7 percent had 

 survived in the protected area, less than 7 percent in the unprotected. 

 Details of a special suction sampler are given. Experiments with hard 

 clam larvae showed that there was no apparent preference for setting on 



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