NOTE Beal et al : Shell marker for juvenile, hatchery-reared Mya arenaria 



383 



0KV X18 10e0U 088 06082 UM 







Figure 1 (continued) 



dividuals was 19.6 ±0.24 mm SE (Fig. 3B), which 

 equates to an average gi-owth rate of 0.093 mm/day. 



Discussion 



Our data provide evidence of a distinctive mark or 

 Une being formed on the outer surface of the valves 

 of juvenile hatchery-reared softshell clams. We have 

 observed from other field tests and stock enhance- 



ment trials in Maine that the mark may be present 

 for up to 1.5 years after planting, after which, the 

 line disappears as the umbo region of the shell be- 

 comes increasingly worn, presumably on account of 

 sediment abrasion from burrowing or seasonal repo- 

 sitioning (Zwarts and Wanink, 1989). 



The formation of the line on the shell surface be- 

 tween the umbo and the ventral margin allows one 

 to distinguish easily between wild and cultured ju- 

 venile clams and can be a valuable tool for resource 



