Figure 1. — Upper valve of sea scallop showing strong shock rings and weak annual rings. 



the circuli are more closely spaced and give the 

 appearance of a band or ring (fig. 2). These 

 bands are laid down annually as the result of a 

 decrease in the rate of growth much as has been 

 demonstrated for tree rings and fish scales. Al- 

 though the cause has not yet been demonstrated, 

 we believe that it is low winter temperatures. 

 Specimens from shallow water (fig. 3), where 

 winters are more severe, have more prominent 

 rings than those from deeper water where tem- 



peratures vary less. Georges Bank, with an 

 average annual temperature range of 8°-12° C, 

 has a particularly equable climate for sea scallops. 

 Posgay (1953) has shown that sea scallops grow 

 fastest at about 10° C. In his experiments, 

 the rate dropped to about 95 percent of the 

 maximum at 8° C. and to about 80 percent at 

 12° C. 



In addition to the annual rings, most sea scallop 

 shells exhibit other annuli which mark nonannunl 



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U.S. FISH AND WILDLIFE SERVICE 



