PETKRSON ETAL.: MARK- RECAPTURE TEST OF HARD CLAMS 



tion was consistently lower than when the band was 

 not being deposited. The magnitude of the ratio of 

 these two different growth rates varied considerably 

 from 1.01 to 3.27. The major reason for this 

 variability was probably the logarithmic nature of 

 growth in M. mercenaria. All clams chosen for this 

 analysis of daily lines were young (1-3 yr old at 

 introduction in June 1978) and within a size range (3- 

 6 cm long) where the rate of decline in absolute 

 growth rate with increasing size is substantial. Con- 

 sequently, in those clams where the annual band fell 

 at the end of the time period that was analyzed, the 

 inherent logarithmic growth pattern enhanced the 

 apparent difference in growth rate in- and outside of 

 the period of annual band deposition. Conversely, 

 when the annual band fell at the beginning of the time 

 period analyzed, the relative difference in growth 

 rate was masked by the inherent general pattern of 

 slowing of growth with increased size. Despite this 

 dependence on the band's position within the growth 



interval analyzed, it is clear that the period of annual 

 band deposition represents a time of relatively 

 slow growth. 



0-Year Class 



In the 432 0.25 m 2 samples taken in February-April 

 1980 from Back Sound, we collected 546 M. mer- 

 cenaria. Only 9 individuals (all<1.25 cm long) lacked 

 evidence of a growth band, whereas 126 contained a 

 single annual band. (The other 411 clams contained 

 more than one band.) Assuming that virtually all 

 clams in the 0-year class had grown sufficiently by 

 winter (February-April) to be efficiently captured in 

 our sampling process (this assumption is tested 

 below), then the fraction 9/135 (6.7%) estimates the 

 frequency of error made in assuming that all clams in 

 the 0-year class are branded with their first identifi- 

 able growth band in their first fall season. This result 

 implies that we underestimate the age of a relatively 



APRIL + MAY 



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SEPTEMBER + OCTOBER 



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SIZE AT FIRST BAND 



0.5 



2.5 3.0 



LENGTH (cm) 



3.5 



4.0 



4.5 



FlGl'RE 5.— The size (length)-frequency distributions of all unmarked Mercenaria mercenaria 

 recruits collected and removed at two seasons (fall and spring) from fixed 1 nr enclosures in Mid- 

 dle Marsh, as compared with the distribution of size ( length) at first band for all clams collected in 

 January-February 1980 from Johnson Creek. Core Sound, N.C. See text for details on 

 methods. 



773 



