88 



Fishery Bulletin 98(1) 



managers J and is a prototype experiment for adaptive 

 management of shellfisheries in southeastern North 

 America. 



Methods 



Study sites 



The intertidal oyster reefs used in this study were located 

 in two large tidal creeks, Pages and Whiskey Creeks, sit- 

 uated on the Intercoastal Waterway near Masonborough 

 Inlet, Wilmington, North Carolina. The two creeks con- 

 sisted of well-flushed sandy to muddy bottom tidal chan- 

 nels 0-2 m in water depth. Channels in each creek were 

 separated by small to large patches of marsh iSpartina 

 alterniflora ) habitat surrounded by oyster reefs created 

 by Crassostrea virgimca. The two creeks were chosen 

 because they have been permanently closed to fishing for 

 about the last ten years owing to high coUform bacteria 

 counts caused by the seepage of septic tanks from sur- 

 rounding homes. Both creeks are highly productive, sup- 

 porting large populations of fishes, birds, crabs, clams, 

 and oysters. Tides in each creek are predominantly M-2 

 lunar tides, and the tidal range is 1-2 m in both creeks. 

 Four large oyster reefs (9-13 m wide x 45-55 m long), 

 each containing relatively high densities of oysters and 

 hard clams, were chosen in each creek. The reefs were 

 situated 150-200 m from the mouth of each creek. The 

 salinity near the experimental reefs was 22-34 psu 

 throughout the course of the experiment and water tem- 

 perature was 3-30°C. 



Three to five permanent 6-m long x 1-m wide tran- 

 sects were established haphazardly on each oyster reef 

 by using PVC poles with rebar anchors between 1-14 

 June 1996. A total of sixteen transects were estab- 

 lished in each creek at approximately 0.5 m above 

 the mean low tide level. The sixteen transects pro- 

 vided a total of four replicates of each of the following 

 four harvest treatments: clam harvesting only, oyster 

 harvesting only, clam harvesting and oyster harvest- 

 ing combined, and no harvesting. Reefs and transects 

 were located in areas where disturbances caused by 

 shellfishing, boat traffic, or other human activities did 

 not normally occur. We found no evidence suggesting 

 that experimental reefs were physically or chemically 

 disturbed throughout the course of the experiment. 



Sampling of clams and oysters 



The density of live and dead oysters on each experi- 

 mental oyster reef was measured between 5 and 10 



^ Carpenter, R., and M. Marshall. 1996. North Carolina Division 

 of Marine Fisheries, 3431 Arendell St., Morehead City, NC 28557. 



July 1996 before harvest treatments were applied. 

 Oyster density was measured by counting (but not 

 removing) oysters in three 0.25-m^ permanent plots 

 established in each of the sixteen transects in each 

 creek. Plots were established by stretching a measur- 

 ing tape between the two PVC poles marking each 

 transect and by placing a PVC quadrat at 0.5-, 2.5-, 

 and 3.5-m distance. All live and dead oysters were 

 counted in each quadrat. The density of naturally col- 

 onized clams was not determined prior to the appli- 

 cation of harvest treatments to avoid disturbing the 

 reefs and potentially influencing the condition of the 

 remaining clams and oysters. Instead, between 5 and 

 10 July, 16 hatchery-raised clams provided by ARC, 

 Inc. of Atlantic, North Carolina, were placed in each 

 of three 1-m- quadrats established within each 6-m 

 transect. This introduction of transplanted clams was 

 done to assure that enough clams were present for 

 the experiment. The 1-m- quadrats were also placed 

 at 0.5, 2.5, and 3.5 m distance along the transects. 

 Before being transplanted, hatchery clams were dyed 

 in Alizarin red dye in order to distinguish them from 

 natural clam populations (Peterson et al., 1995). Of 

 the 16 clams in each plot, eight were 20-25 mm in 

 length, and eight were 27-32 mm in length. 



Between October 1996 and March 1997, oysters were 

 harvested with hand tongs during low tides within the 

 1 ) oyster harvesting and 2 ) clam and oyster harvest- 

 ing treatments. Oysters were harvested for the same 

 total period of time (3.75-4.0 h/transect) along the 

 entire length of each transect. From August 1996 to 

 May 1997, clams were harvested during low tides with 

 clam rakes and clam tongs from the 1 ) clam harvest- 

 ing and 2) clam and oyster harvesting treatments, 

 and for approximately the same total period of time 

 (i.e. 3.75-4.0 h/transect). The total number of natu- 

 rally occurring and transplanted clams and oysters 

 removed during the harvest was recorded. All harvest- 

 ing was conducted by R. A. Cummings, a professional 

 shellfisherman. 



The density of live and dead clams and oysters 

 remaining on experimental reefs was sampled 10-23 

 July 1997, after termination of the harvesting treat- 

 ments. Clams and oysters were sampled several months 

 after the last clam harvesting in May so that any poten- 

 tial long-term effects of harvesting were realized. For 

 example, unharvested clams and oysters remaining on 

 reefs may have been injured during harvesting and 

 died after several weeks. Oysters were sampled by plac- 

 ing a measuring tape along the transects and counting 

 all oysters within the three 0.25-m2 quadrats at 0.5-, 

 2.5-, and 3.5-m distance along each transect. Clams 

 were sampled by digging up the top 25 cm of sediment 

 from each 1-m- sampling plot. The sediment was then 

 passed through a 1-mm sieve to remove all clams. 



