FISHERY BULLETIN: VOL. 82, NO. 2 





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5mm 



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,500 um, 



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FIGURE 3. — iai Right valve of a 6-yr-old ocean quahog, Arctica islandica, 33.1 mm shell length, lb) Sectioned anterior portion of the 

 left valve showing injury, ic) Three serial photomicrographs of the acetate peel image. Arrows point to annuli formed before and after 

 the injury. (d> Photomicrograph of the acetate peel image of the hinge tooth showing six annuli. 



Size measurements at age of the clams are 

 shown in Figure 6. The mean shell length, one 

 standard deviation from the mean, and range are 

 given for clams 3-8 yr old. The bands on the shells 

 and lines in the peels indicated rapid growth 

 through age 8. From age 3 and a mean size of 23.4 

 mm, the clams increased about 5 mm in shell 

 length each year to age 8 and a mean size of 46.1 

 mm. Thereafter, growth seemed to decrease in 

 rate. The bands were well separated to age 13. The 



bands at the ventral margin of 14-yr-old and older 

 clams were too indistinct for accurate mea- 

 surements, but the growth lines in peels were 

 clearly separated and easily counted. The oldest 

 14- to 18-yr-old specimens may have been the 

 smallest and slowest growing individuals in their 

 year classes, but mean lengths were not progres- 

 sively smaller than means for clams 9-13 yr old. 

 Thus, a significant bias was not clearly indicated 

 in the selection of older specimens. 



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