FISHERY BULLETIN: VOL. 85, NO. 2 



ronmental consequences of the utilization of new, 

 alternative technologies. 



Fisheries for the hard clam, Mercenaria mercen- 

 aria (L.), and other sedentary benthic invertebrates 

 require the use of either hand implements (rakes, 

 hoes, etc.) or boat-drawn gear (dredges, trawls, etc.). 

 Managers of benthic invertebrate fisheries may turn 

 to the subdiscipline of benthic ecology to seek predic- 

 tions of the relative environmental and ecological 

 consequences of utilizing various alternative fishing 

 gears or of permitting technologically new substitu- 

 tions for traditional fishing methodologies. Unfor- 

 tunately, benthic ecologists are frequently unable 

 to provide confident answers to many questions, 

 often either because the fisheries applications in- 

 volve a far larger scale than can be or has been prac- 

 tically accommodated in basic experimental research 

 designs or because the questions fall into an area 

 of current debate and ongoing study in the basic 

 science of the field. 



One might take, as an example of the poor predic- 

 tive capacity of benthic ecology, the question of 

 whether widespread adoption of mechanical har- 

 vesters by commercial M. mercenaria fishermen will 

 affect the future recruitment success of M. mercen- 

 aria in the local area of harvest. Most fisheries 

 biologists agree that the mechanical harvesters are 

 more efficient in gathering hard clams from a given 

 area and cause more physical disruption of the bot- 

 tom than the alternative hand methods of raking and 

 tonging. Even given these assumed differences, ben- 

 thic ecology provides mixed and conflicting predic- 

 tions of the impact of switching to mechanical 

 harvesters. Basic studies of adult-larval interactions, 

 including some among suspension-feeding bivalves 

 (Woodin 1976; Williams 1980; Peterson 1982b), 

 might suggest that removal of large, adult suspen- 

 sion feeders would enhance the survivorship of 

 settling larvae and thereby increase the recruitment 

 success of M. mercenaria in the efficiently harvested 

 areas. Yet, the experimental results on which such 

 a prediction is based were achieved on a much 

 smaller spatial scale and probably depend upon ab- 

 solute density (or feeding rate) of all suspension 

 feeders in an unspecified way. It is conceivable that 

 the virtual removal of M. mercenaria over a substan- 

 tial area might remove an important settlement cue 

 (produced by adults) needed for larval habitat selec- 

 tion (e.g.. Meadows and Campbell 1972; Gray 1974). 

 If this were true, recruitment success of M. mercen- 

 aria would decline with the intensity of harvest. 

 Similarly, benthic ecology provides conflicting pre- 

 dictions about the effects of the increased physical 

 disburbance of mechanical harvesting on recruit- 



ment success of M. mercenaria. On the one hand, 

 M. mercenaria recruits might be expected to suffer 

 increased mortality from burial during massive sedi- 

 ment disturbance (Rhoads 1974; Myers 1977; Thistle 

 1981; Wilson 1981). Yet, larvae of many species 

 settle more densely into disturbed bottoms (Gray 

 1974; McCall 1977; Hulberg and Oliver 1980). Again, 

 these signals are conflicting but, even more impor- 

 tantly, experimental benthic ecology is unable to 

 predict adequately whether the scale and intensity 

 of disturbance during commercial clam harvesting 

 are appropriate to invoke either of these processes. 

 Because of the restricted scale of past field ex- 

 periments and the consequent limitations of benthic 

 ecology in the applied arena, we designed controlled 

 field experiments to test the impact of mechanical 

 clam harvesting on a large scale, sufficient to pro- 

 vide environmental data to resource managers and 

 to extend simultaneously the scope of basic experi- 

 mental, benthic ecology. Specifically, we tested on 

 a 1,225 m^ scale whether the harvest of M. mercen- 

 aria, with its attendant physical disruption of the 

 bottom, affected the 1) recruitment success of M. 

 mercenaria, 2) biomass of seagrasses, 3) density of 

 bay scallops, and 4) density of all other benthic 

 macroinvertebrates. We tested these harvest effects 

 in each of two common estuarine habitats, a sand 

 flat and a seagrass bed, and followed not only the 

 immediate response to harvesting but also the 

 changes in most variables over a subsequent 3.5-yr 

 period. Thus, the need for ecological data to use in 

 fisheries management provided an opportunity to 

 expand the temporal and spatial scale of experi- 

 ments in marine benthic ecology and thereby eval- 

 uate our ability to extrapolate from previous theory 

 based on smaller scales. 



METHODS 



To test whether the type and/or intensity of hard 

 clam, Mercenaria mercenaria (L.), harvest has any 

 detectable effect on 1) its own recruitment, 2) sea- 

 grass biomass, 3) bay scallop, Argopecten irradians, 

 density, or 4) density of small benthic macroinverte- 

 brates, we performed a large-scale field experiment 

 at sites along the southern (barrier island) margin 

 of Back Sound near Beaufort, NC (Fig. 1). This ex- 

 periment was conducted in a seagrass meadow and 

 in an unvegetated sand flat approximately 500 m 

 to the west to permit a test of whether effects of 

 harvest vary with habitat. This general area and its 

 physical characteristics are described in several 

 previous publications (Sutherland and Karlson 1977; 

 Nelson 1979; Peterson et al. 1983b, 1984). Back 



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