PETERSON ET AL: MARK-RECAPTIRE TEST OF HARD CLAMS 



35' 



34°45 - - 



40-- 



40 



12 3 4 



kilometers 



76° 40 



35' 



30' 



25' 



FIGURE 1. — Geographic relationships among study and collection sites in the Cape Lookout vicinity of North Carolina: MM I — the site of the 

 mark-recapture experiment in a seagrass, Znstera manna, meadow at Middle Marsh and of the fixed 1 m 2 enclosures sieved seasonally for new- 

 recruits; MM II — the other site of fixed 1 m : enclosures sieved seasonally for new recruits on a muddy-sand flat near the west end of Middle 

 Marsh; JC — the Johnson Creek collection site in Core Sound; BSS andBSG — the sand flat and the seagrass sites (respectively) in Back Sound 

 from which 0-year class Mercenaria mercenaria were collected in February- April 1980 for estimation of the proportion without an annual 

 band. 



mercenaria by systematically plowing with fingers to 

 a 10 cm depth followed by in situ sieving with 6 mm 

 mesh to that same depth. This process permitted 

 establishment of constant M. mercenaria density 

 across all treatments and all replicates. The same 

 procedure was also used to recover all marked clams 

 from each plot on 20 September 1978 and on 21 April 

 1979. On those dates, each marked clam was 

 remeasured and returned within 1 h to its assigned 

 plot. On both those dates and on all four dates when 

 clams were sacrificed for shell analyses, tops and par- 

 tial tops were removed and replaced with new mesh 

 to prevent extensive fouling. On the first two dates 

 (17 October 1979 and 22 May 1980) when clams 

 were sacrificed and returned to the laboratory for 

 shell analyses, all clams were again excavated by this 

 same sampling procedure and remeasured. Those 



not sacrificed were returned to their assigned plots 

 within 1 h. On the two subsequent sampling 

 occasions, no remeasuring occurred and a preset 

 number of clams was removed from each field plot 

 without excavating the others. 



In the laboratory, we used calipers and a fine, felt- 

 tipped pen to locate and mark on the outer shell sur- 

 face of each clam its size at each measurement date 

 (including size at introduction). A low-speed Buehler 

 Isomet saw with a diamond blade was used to cut the 

 marked valves from umbo to the ventral margin along 

 the axis of greatest growth (Pannella and MacClin- 

 tock 1968; Rhoads and Pannella 1970). This cut 

 revealed the cross-sectional growth surface, which 

 was then sanded with increasingly fine-grained grit 

 and polished with alumina powder on a polishing 

 wheel. We examined macroscopically the polished 



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