MURAWSKI ET AL.: GROWTH OF OCEAN QUAHOG, ARCTICA ISLANDICA 



Table 3.— Back-calculated growth (shell length, in millimeters) of small ocean quahogs. Samples taken from lat. 40°25' 



N, long. 72°24' W, 26-29 July 1978, in the Middle Atlantic Bight. 



'External mark eroded but mark present in shell cross section 



"Number of annuli exceeds the number of lengths at annulus because marks could be distinguished in shell cross sections that were too 

 closely spaced to discern on shell surfaces. 



lengths at capture were also determined (Table 

 3). 



Specimens recaptured in 1979 ranged in shell 

 length from 59 to 104 mm, most had a deep 

 brown or black periostracum. Several specimens 

 did, however, exhibit the characteristic external 

 banding pattern (Fig. 1), and were useful in vali- 

 dating the presumed annual periodicity of 

 marks. 



Marginal shell growth beyond the last exter- 

 nal mark was strikingly different among small 



ocean quahogs from August 1979 and February 

 1980 samples. Mean lengths at capture for indi- 

 vidual age classes from summer 1978 (particu- 

 larly ages 1-9) were substantially greater than 

 lengths at the last annulus, and were nearly 

 equivalent to mean lengths at the last annulus for 

 the next age class (Table 3). Ocean quahogs from 

 winter 1980 invariably had formed or were 

 forming an annulus at the shell margin (Fig. 1). 

 A similar pattern was noted in shell cross 

 sections. 



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