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Fishery Bulletin 98(1) 



trast, there were greater numbers of missing trans- 

 planted clams at Pages Creek than at Whiskey Creek. 

 Harvest type, specifically clam harvesting, influenced 

 the number of live transplanted clams but had no sig- 

 nificant effect on the number of dead or missing trans- 

 planted clams. Fewer live, transplanted clams were 

 found in clam-harvested plots than were found in con- 

 trol plots at both sites (Fig. 5). Because few of the 

 transplanted clams were removed from reefs by exper- 

 imental harvesting, the negative effects of clam har- 

 vesting on densities of live, transplanted clams may 

 be explained by increased clam mortality caused by 

 clam harvesting. Overall, the effects of shellfish har- 

 vesting appear to be more variable and unpredictable 

 for clams than for oysters. Our results indicate that 

 both types of shellfish harvesting can have negative 

 impacts on clam populations, but that this is a site- 

 specific phenomenon. 



PJesults of this study do not support the hypothesis 

 that harvesting reefs for both clams and oysters has a 

 negative synergistic impact on clam and oyster popu- 

 lations. Clam and oyster harvesting alone had similar 

 negative effects on densities of live oysters, and the joint 

 harvesting of both species on the same reefs did not 

 decrease the density of live oysters any fuither. Simi- 

 larly, the negative effects of clam harvesting on the den- 

 sity of live clams, and on survival of hatchery-raised 

 clams were not enhanced when oyster harvesting was 

 applied in combination wdth clam harvesting. Thus, the 

 combined harvesting of both clams and oysters on inter- 

 tidal reefs does not cause greater direct or indirect mor- 

 taUty of shellfish populations than that caused by clam 

 or oyster harvesting conducted separately. 



This experimental analysis has important implica- 

 tions for the management of intertidal oyster reefs and 

 their associated molluscan fishery resources. First, 

 maintaining high densities of oysters on some inter- 

 tidal reefs, by preventing both clam and oyster har- 

 vesting, may help to preserve future oyster harvests 

 and brood stock. Protecting some reefs from shellfish- 

 ing will also help preserve the many ecological ser- 

 vices that oysters and oyster reefs provide, such as 

 improving water quality through the filtration of sus- 

 pended particles (Officer et al., 1982; Dame et al., 

 1984; Newell, 1988) and creating essential recruit- 

 ment, refuge, and foraging habitat for economically 

 valuable fishes and crabs (Bahr and Lanier, 1981; 

 Zimmerman et al., 1989; Lenihan et al., 1998). Pre- 

 venting oyster and clam harvesting on some intertidal 

 reefs will also potentially conserve clam populations 

 from both the direct and indirect negative effects of 

 shellfish harvesting, thereby protecting future clam 

 harvests and brood stock. Overall, allowing the har- 

 vest of both clams and oysters on some natural and 

 restored oyster reefs is a rational option because the 



combined effect of both clam and oyster harvesting is 

 no greater than the effect of each harvesting activity 

 conducted alone. Thus, we recommend that both types 

 of harvesting be allowed on some reefs but that other 

 reefs be protected as refuges for shellfish populations 

 and other reef-associated fauna. 



In adaptive fishery and habitat management, the 

 results of relatively small-scale, prototype experi- 

 ments, like the one reported here, are used to design 

 larger-scale comparisons of potential management 

 options. Therefore, we recommend that the results of 

 our experiment be used to design alternative shell- 

 fishery management options that can be implemented 

 and monitored on relatively large spatial and tempo- 

 ral scales in North Carolina and other coastal states of 

 North America. Our recommendation that some natu- 

 ral and restored oyster reefs be closed from shellfish 

 harvesting and others opened or restored for the pur- 

 pose of both clam and oyster harvesting can be used to 

 identify potential management options. Further test- 

 ing of the generality of our findings on larger spatial 

 and temporal scales is necessary because our study 

 was conducted at only two sites and over a one-year 

 period. Therefore, our results may not apply to areas 

 with different environmental conditions (e.g. different 

 flow and sedimentary regimes, areas of low recruit- 

 ment) and hai-vesting intensities (e.g. very low and 

 high levels of hai-vesting). It is necessary to determine 

 with experiments and simulation models how much 

 oyster reef habitat should be preserved from harvesting 

 to maintain sustainable oyster and clam brood stock 

 populations and habaitat for the successful recruitment 

 and sunaval of other fishery organisms. 



The following steps should now be taken by fishery 

 and habitat managers to improve management of the 

 clam and oyster populations and intertidal oyster reef 

 habitat: 1 ) identify overall management goals and pos- 

 sible options; 2) derive specific predictions based, at 

 least in part, on the experiment results reported in this 

 study; and 3) design monitoring programs to quantify 

 the effect of each management option. Whenever pos- 

 sible, it is highly recommended that fishermen, fish- 

 ery managers, and ecologists be included in designing 

 and monitoring large-scale management experiments 

 because collectively they will provide the highest level 

 of rigor and reality. 



Acknowledgments 



We thank R. A. Cummings for helping to design and 

 conducted the experimental harvests. We thank M. 

 Marshall, D. Meyers, C. H. Peterson, H. C. Summer- 

 son, and G. W. Thayer for advice; R. Carpenter for 

 helping to select experimental sites; and D. Bockus, 



