Lenihan et al.: Conserving oyster reef habitat 



303 



A significant treatment effect in the after period 

 (Table 2) indicated that the change over time in 

 proportion of dead oysters varied among harvest 

 treatments. Tonging and dredging increased the 

 fraction of dead among in situ oysters on reefs 

 (SNK; P<0.05; Fig. 3B), but diver-harvesting 

 did not. Immediately after harvesting, divers 

 found that many oysters on tonged and dredged 

 reefs had been broken open, severely cracked, or 

 punctured. 



Discussion 



Our comparisons of gear revealed relatively 

 unambiguous differences in their harvesting 

 efficiency for oyster dredges, tongs, and hands 

 of divers. Dredging and tonging had similar and 

 statistically indistinguishable catch efficiencies, 

 which seems reasonable given that both tech- 

 niques are commonly employed in the same loca- 

 tions and times in the oyster fishery. Presumably, 

 fishermen choose between these two gears on the 

 basis of personal preference, history, and skill, as 

 well as on the basis of water depth, bottom type, 

 and other factors that did not vary in our study. 

 Diver-harvesting of oysters resulted in higher 

 rates of harvest per hour, but this enhancement 

 in catch efficiency required the presence of two 

 people, one diver beneath the surface and another 

 person on deck involved in hauling baskets of 

 oysters onto the deck and culling out market- 

 able oysters. Because the increase in efficiency 

 was only 25-32%, this enhancement falls short of 

 the 100% required to compensate each fisherman 

 to the same degree that dredging and tonging pro- 

 vide. Nevertheless, the immediate economics of 

 diver-harvesting could prove competitive or even 

 superior if the single deckhand could serve two or 

 more divers, which seems likely from our experi- 

 ence with the workload on deck, and if the oysters 

 taken are priced more favorably because of larger 

 size or less damage, which seems possible. A 

 complete short-term economic comparison would 

 need to include higher costs for fuel in dredging 

 and costs of filling air tanks for diving, as well as 

 depreciation of gear. 



This discussion of the basic efficiencies and eco- 

 nomics of the methods of commercial oyster fish- 

 ing is based upon short-term considerations only. 

 That short-term time perspective is the cause of 

 failures to achieve sustainability in fisheries quite 

 generally (Ludwig et al., 1993; Botsford et al., 1997). We 

 show that adoption of hand-harvesting by divers would 

 result in substantially less fishery-induced reduction in 

 reef height by a factor of four to six, implying greater 

 preservation of the habitat and thus a more sustainable 

 fishing practice. Our data on the changes in area covered 

 by reefs as a function of harvest treatment revealed only 

 small differences among treatments. The height of a reef 



40 



30 



20- 



10 



control diver- longed dredged 

 harveted 



Before 



control diver- tonged dredged 

 harveted 



After 



control diver-harvested tonged 



dredged 



Figure 3 



Mortality of oysters caused by various harvesting techniques. (A) 

 Mean ( + SE) % dead within oyster populations on experimental 

 reefs before and after being harvested by three different harvest- 

 ing techniques: dredging, tonging, and diver-harvesting. Control 

 reefs were not harvested. Letters represent results of SNK post hoc 

 tests: dredged, after>tonged, after>all other treatments at P<0.05. 

 There was no difference among treatments before harvesting. (B) 

 Mean ( + SE) absolute difference in the % dead oysters on experi- 

 mental reefs before and after harvesting. Difference calculated by: 

 \9o after-% before]. Letters represent results of SNK post hoe tests: 

 dredged and tonged>diver-harvested and control at P<0.05. 



is a critical variable in sustaining the reef as an engine of 

 oyster production because short reefs can be easily covered 

 by sediment (Lenihan, 1999), can be abraded by sediment 

 transport (Lenihan, 1999), and can fail to extend above 

 hypoxic bottom waters (Lenihan and Peterson, 1998). 

 Tall reefs (i.e., reefs not degraded by harvesting) produce 

 faster flow speeds and more turbulence for oyster popula- 

 tions, which in turn increase oyster growth rate, increase 



