Annual increment 

 Year class Mercenaria/m^ in mean wt Production increment 



Gp 11:1972 



2.41 



0.019 



0.05 





1971 



0.88 



0.148 



0.13 





1970 



4.75 



0.466 



2.21 





1969 



0.88 



0.759 



0.67 





1968 



1.25 



0.637 



0.80 





1967 



0.13 



0.629 



0.08 





1965 



0.38 



0.123 



0.05 





lp 111:1972 



2.43 



0.018 



0.04 





1971 



3.67 



0.141 



0.52 





1970 



12.29 



0.448 



5.51 





1969 



1.00 



0.733 



0.73 





1968 



9.43 



0.617 



5.82 





1967 



0.43 



0.609 



0.26 





1966 



0.58 



1.094 



0.63 





1965 



4.15 



0.119 



0.49 





Gp IV:1972 



3.44 



0.019 



0.07 





1971 



2.59 



0.147 



0.38 





1970 



2.13 



0.467 



0.99 





1969 



0.71 



0.765 



0.54 





1968 



2.13 



0.642 



1.37 





1967 



0.71 



0.635 



0.45 





1966 



0.24 



1.141 



0.27 





1965 



2.36 



0.124 



0.29 





<1965 



1.41 



1.301 



1.83 













J.L.M. 



COR 



Hibbert, C. J. 1977. 



Growth and survivorship in a tidal-flat population of the bivalve Mereenaria 

 meveenavia from Southampton Water. Mar. Biol. 44(1): 71-76. 



Hard clam in Southampton Water, England probably was introduced in 1925, 

 when a "few dozen" clams were placed opposite Marchwood Power Station in the 

 River Test. Now it has spread throughout Southampton Water and the eastern 

 Solent, living mainly in the intertidal zone. To derive smooth growth 

 curves for clams sampled between July 1972 and Sept 1973 it was assumed that 

 no growth occurred from Oct to April in 1967 to 1972 year classes and no 

 growth until June in 1965 and 1966 year classes. Growing season was assumed 

 to be from about May or July until Sept. A year's growth (estimated from fig. 

 1) was from about 5 mm shell length in July to about 25 mm in Sept (14 months 

 later) for the 1972 year class, and from about 68 mm to 73 mm over the same 

 period for the 1965 year class. Seasonal cycles in flesh weight and calorific 

 content appeared to be related to gonad proliferation and subsequent spawning. 

 Recruitment is sporadic and probably depends on spawning of upstream 

 populations, where conditions are more favorable for larval development. 

 Successful sets every 3 or 4 yrs appear to be related to low summer water 

 flow in the River Test. Growth at Hamble was closely related to water temp. 

 Growth did not begin until water temp rose above 9°C, and ceased by Oct 

 although temps were still above 11°C in Nov. Absence of phytoplankton may 

 be the main growth-limiting factor at end of season. Mortality was caused 

 largely by predation. Predation on clams less than 2 yrs old probably is 

 mainly attributable to shore crab Carainus maenas . Small clams also are 

 eaten by certain demersal fishes and some birds. Herring gulls were 

 principal predators on larger clams. - J.L.M. 



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