FISHERY BULLETIN: VOL. 82, NO. 1 



Thompson et al. (1980a) reported that the predicted 

 radiometric age of an ocean quahog having 22 bands 

 corresponded exactly to 22 yr when aged using 228 Ra. 

 Turekian et al. (1982) concluded that age deter- 

 minations of ocean quahogs from radiometric 

 analyses are compatible with counts of bands formed 

 annually. Thus, radiometric studies support the con- 

 tention of an annual periodicity of growth lines in 

 ocean quahogs. 



Various environmental disturbances have been 

 implicated in the formation of shell abnormalities 

 and atypical growth lines in other bivalve species 

 (Weymouth et al. 1925; Shuster 1957; Merrill et al. 

 1966; Clark 1968; Palmer 1980). It is therefore, con- 

 ceivable that the stress imposed by dredging, mark- 

 ing, and returning the ocean quahogs to the ocean 

 floor and their burrowing activities hastened the for- 

 mation of a growth line in 1978. Thereafter, natural 

 events affecting the metabolism of shell deposition 

 are more likely stimuli. Such events apparently did 

 not occur during the period after the formation of the 

 growth line in 1978 and recovery of clams in late 

 August 1979. Instead a growth line that in all prob- 

 ability had formed in 1979 was found in the shells of 

 clams recovered on 9 September 1980. Its formation 

 may have occurred in late August 1979, but the third 

 line found in half of the clams recovered on 9 Septem- 

 ber 1980 suggests the possibility of its formation in 

 early September 1980. By inference, then, growth 

 line formation in 1979 and 1980 occurred in 

 September. 



The reported life span (150 yr, Thompson et al. 

 1980a) of ocean quahogs surpasses similar estimates 

 for other bivalves. Age and growth of the far east 

 mussel, Crenomytilus grayanus, have been deter- 

 mined from examinations of shell structure, an 

 oxygen-isotope method, and notching experiments 

 (Zolotarev 1974; Zolotarev and Ignat'ev 1977; 

 Zolotarev and Selin 1979). These investigations 

 indicated that longevity of the mussel may exceed 

 100 yr. Turekian et al. (1975) proposed a longevity of 

 about 100 yr for a deep-sea nucoloid, Tindaria callis- 

 tiformis, after determining ages by radiometric 

 means and counting regularly spaced bands in the 

 shell of one of the largest (8.4 mm in shell length). It 

 seems likely that longevity of ocean quahogs may 

 exceed 150 yr. Murawski and Serchuk (1979) report- 

 ed a maximum shell length of 131 mm for ocean 

 quahogs in extensive collections taken from the Mid- 

 dle Atlantic Bight. A specimen of this size is half 

 again as large as the 88 mm example of a 149-yr-old 

 ocean quahog reported by Thompson et al. 

 (1980a). 



In conclusion, the foregoing description of annual 



growth line formation in marked ocean quahogs and 

 analyses of growth in the same specimens by 

 Murawski et al. (1982) present significant supporting 

 evidence for the hypothesis of slow growth and a long 

 life span in the species. Ocean quahogs apparently 

 live longer than any other bivalve known to man. 



ACKNOWLEDGMENTS 



We thank Brenda Figuerido and John Lamont for 

 their assistance in preparing the art work and 

 photographs, and Ida Thompson, University of Edin- 

 burgh, Department of Geology, King's Building, 

 Edinburgh EH 9 3JW, Scotland, for encouragement 

 in undertaking the study and helpful comments on 

 the manuscript. 



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