NOTE Bishop et al.: Effects of harvest methods on sustainability of a bay scallop fishery 



713 



Implementation of gear restrictions that allow only 

 hand methods of harvesting scallops (i.e., hand, rake, 

 dip nets) may minimize impacts of harvesting on scallop 

 recruits by reducing damage to seagrass and the loss 

 of juvenile bay scallops that comprise the year class 

 that will be fished in the following year. Although such 

 restrictions were introduced to Bogue Sound in 1992 

 in response to the 1987 red tide that decimated scallop 

 populations in that water basin (Summerson and Peter- 

 son, 1990), this conservation-based measure was discon- 

 tinued in 1998 because of social pressure from fisher- 

 men. In the present study, we ascertain the impacts of 

 dredges and hand-harvesting methods on the biomass 

 of seagrass, as compared to undisturbed controls, 1) by 

 measuring the biomass of seagrass directly dislodged by 

 each method, and 2) by ascertaining, through measure- 

 ments of biomass one month later, whether this removal 

 affects the standing stock of seagrass over a longer 

 temporal scale. We also tested both direct and indirect 

 effects of seagrass removal on bay scallop recruits by 

 measuring their density before and one month after 

 harvesting and by ascertaining whether any document- 

 ed difference can be explained by the numbers directly 

 removed by uprooting of seagrass during harvesting. 

 Such an assessment of ecological impacts of dredging 

 on bay scallop recruits is urgently required given that 

 North Carolina landings of bay scallops have fallen to 

 an historic low since the relaxation of gear restrictions 

 (Burgess and Bianchi 3 ). 



Materials and methods 



Nine adjacent experimental plots, 25 mx8 m, were estab- 

 lished as a research sanctuary, closed to commercial 

 fishing activity, in western Bogue Sound, North Carolina 

 (34°41.6'N, 76°59.1'W), prior to the opening of the scallop 

 season in winter 2001-2002. Although this section of 

 Bogue Sound has been closed to scallop dredging since 

 at least 1998, its high-tide water depth of 1.5 m is well 

 within the depth range for harvesting with this method. 

 Plots contained continuous seagrass beds dominated 

 by Zostera marina on a muddy-sand bottom. Three of 

 the plots were randomly assigned to each of the experi- 

 mental treatments: hand-harvested, dredge-harvested, 

 and control (undisturbed). In order to ensure that our 

 treatments were representative of harvesting methods 

 and intensities used by the industry, they were per- 

 formed with participation of an experienced commercial 

 scallop fisherman (Ted Willis of Salter Path). Dredging 

 was achieved with a standard 72-cm wide steel scallop 

 dredge, at an intensity of five parallel tows, each run- 

 ning along the length of the plot within a 10-minute 

 period. This method, which mimicked commercial fishing 



1 Burgess, C. C, and A. J. Bianchi. 2004. An economic 

 profile analysis of the commercial fishing industry of North 

 Carolina including profiles for state-managed species, 243 p. 

 North Carolina Division of Marine Fisheries, 3441 Arendell 

 Street, Morehead City, NC 28557. 



practices, minimized overlap between the dredge paths. 

 Hand scalloping involved a single fisherman collecting 

 scallops from the bottom by hand, also during 10-minute 

 periods. Care was taken to ensure that the treatments 

 were applied evenly over the entire plot to avoid creating 

 large within-plot variance that might preclude detection 

 of differences among plots. 



Seagrass and scallops collected during harvesting 

 were retained for measurements. The number of adult 

 scallops (>40 mm shell height; Peterson et al., 1989) 

 obtained with each of the methods of harvest was enu- 

 merated. The size (to the nearest 0.1 mm) and number 

 of juvenile scallops collected as bycatch and the dry 

 weight of seagrass removed during harvesting were 

 quantified separately. Because not all seagrass and 

 juvenile scallops displaced by harvesting are retained 

 in the dredge or by a fisherman collecting scallops by 

 hand methods, an 8-m long net with 5-mm mesh that 

 extended from the bottom to the surface was set down- 

 stream from each plot and perpendicular to the flow 

 of the current during harvest. The nets were strung 

 between stakes marking the corners of the experimental 

 plot. Dislodged juvenile scallops and seagrass collected 

 by the nets were added to the amounts extracted from 

 the dredge to compute displacement totals. Nets were 

 also set downstream of controls to determine natural 

 rates of transport of seagrass and juvenile scallops that 

 could not be attributed to harvesting operations. 



Each plot was sampled on 14 January 2002, immedi- 

 ately prior to harvesting on that same day to determine: 

 1) the density of bay scallop recruits (size s40 mm; 

 Peterson et al., 1989); 2) the size distribution of the 

 recruits; and 3) biomass per unit of area of seagrass. 

 These variables were resampled on 25 February 2002, 

 over one month later, to ascertain any lasting impact 

 of harvest. Sampling of scallops was conducted with a 

 0.5-m' 2 cylindrical quadrat, haphazardly positioned at 

 nine locations within each plot. A 1.2-cm tall cylinder 

 of 6-mm nylon mesh, attached to the quadrat and sus- 

 pended by a buoyant plastic hoop that floated on the 

 surface of the water, isolated the volume of water above 

 each quadrat so that it could be sampled by suction 

 with a Venturi suction device (according to Peterson et 

 al., 1989). The suction device forced 600 mL of water 

 per minute through a 3-mm collecting bag. Suction 

 sampling was necessary because scallops, which typi- 

 cally recline on the bottom, can enter the water to swim 

 when threatened by predators or otherwise disturbed 

 (Peterson et al., 1982). The disturbance caused by suc- 

 tion sampling of only nine small areas was minimal 

 compared to the scale of harvesting disturbance. Upon 

 returning to the laboratory, seagrass was removed from 

 samples for measurement of dry weight biomass and 

 live scallops were counted, measured to the nearest 

 0.1 mm and categorized as adults (>40 mm) or recruits 

 (^40 mm) in the subsequent year class. 



Seagrass was sampled in five replicate 0.25-m 2 areas 

 within each plot by suction dredging inside a 0.56-m 

 diameter circular quadrat to a sediment depth of 12 cm. 

 Previous sampling has shown this method to be success- 



