298 



Abstract -A major cause of the steep 

 declines of American oyster ( Crassos- 

 trea virginica) fisheries is the loss 

 of oyster habitat through the use of 

 dredges that have mined the reef 

 substrata during a century of intense 

 harvest. Experiments comparing the 

 efficiency and habitat impacts of three 

 alternative gears for harvesting oys- 

 ters revealed differences among gear 

 types that might be used to help im- 

 prove the sustainability of commercial 

 oyster fisheries. Hand harvesting by 

 divers produced 25-32^ more oysters 

 per unit of time of fishing than tradi- 

 tional dredging and tonging. although 

 the dive operation required two fish- 

 ermen, rather than one. Per capita 

 returns for dive operations may none- 

 theless be competitive with returns for 

 other gears even in the short term if 

 one person culling on deck can serve 

 two or three divers. Dredging reduced 

 the height of reef habitat by 34 r r . sig- 

 nificantly more than the 23 f r reduction 

 caused by tonging, both of which were 

 greater than the 6 Q < reduction induced 

 by diver hand-harvesting. Thus, con- 

 servation of the essential habitat and 

 sustainability of the subtidal oyster 

 fishery can be enhanced by switch- 

 ing to diver hand-harvesting. Man- 

 agement schemes must intervene to 

 drive the change in harvest methods 

 because fishermen will face relatively 

 high costs in making the switch and 

 will not necessarily realize the long- 

 term ecological benefits. 



Conserving oyster reef habitat by switching 

 from dredging and tonging to diver-harvesting 



Hunter S. Lenihan 



Bren School ol Environmental Science and Management 

 University of California, Santa Barbara 

 Santa Barbara, California 93106-5131 

 E-mail address: tenihamfflbren ucsb edu 



Charles H. Peterson 



Institute of Marine Sciences 



University of North Carolina at Chapel Hill 



Morehead City, North Carolina 28557 



Manuscript approved for publication 

 25 November 2003 by Scientific Editor. 



Manuscript received 20 January 2004 

 at NMFS Scientific Publications office. 



Fish. Bull. 102:298-305(2004). 



Commercial fishing for demersal fish- 

 es and benthic invertebrates, such as 

 mollusks and crabs, is commonly under- 

 taken with bottom-disturbing gear that 

 can inflict damage to seafloor habitats 

 (Dayton et al., 1995; Engel and Kvitek, 

 1995; Jennings and Kaiser, 1998; Wat- 

 ling and Norse, 1998). Habitat damage 

 from dredges and analogous gear, 

 designed to excavate invertebrates 

 that are partially or completely buried 

 beneath the surface of the seafloor, is 

 generally much more severe than the 

 damage caused by bottom trawls ( Collie 

 et al., 2000). Furthermore, impacts on 

 and recovery from bottom-disturbing 

 fishing gear vary with habitat type; 

 generally smaller effects and more 

 rapid rates of recovery are found for 

 infauna in sedimentary habitats and 

 the most severe and long-lasting 

 damage in biogenic habitats that 

 emerge from the seafloor (Peterson et 

 al., 1987; Collie et al., 2000). Such bio- 

 genic habitats include seagrass beds, 

 fields of sponges and bryozoans. and 

 invertebrate reefs. Biogenic reefs that 

 provide important ecosystem services 

 such as habitat for other organisms 

 include not only tropical coral reefs 

 but also temperate reefs constructed 

 by oysters (Bahr and Lanier, 1981; 

 Lenihan et al., 2001), polychaetes like 

 Petaloproctus (Wilson, 1979; Reise, 

 1982), and vermetid gastropods (Saf- 

 riel, 1975). The recovery of such emer- 

 gent invertebrate reefs is a slow process 

 because of the relative longevity of the 



organisms that provide structure for 

 the reef after they die and because of 

 the nature of reefs as accumulations of 

 multiple generations of reef builders. 



One widespread temperate reef 

 builder, the American oyster iCrassos- 

 trea virginica, also known as the "east- 

 ern oyster," Am. Fish. Soc), has been 

 especially affected by bottom-disturb- 

 ing fishing gear as the target of fisher- 

 ies. More than one hundred years of 

 dredging and tonging oysters in the 

 Chesapeake Bay and Pamlico Sound 

 have caused severe degradation of the 

 oyster reef matrix (deAlteris, 1988; 

 Hargis and Haven, 1988), such that 

 reef area and elevation have been dra- 

 matically reduced (Rothschild et al., 

 1994; Lenihan and Peterson, 1998). 

 Reduction in reef height has a serious 

 consequence for the oyster population 

 because one function of naturally tall 

 subtidal oyster reefs is to elevate the 

 oysters up into the mixed surface layer 

 of the estuary; this layer of mixed sur- 

 face water allows them to avoid mass 

 mortality from persistent exposure to 

 seasonally anoxic and hypoxic bottom 

 water (Lenihan and Peterson. 1998). 

 Reef height and structure also control 

 reef hydrodynamics (e.g., flow speed, 

 turbulent mixing, and particle delivery 

 and deposition), which influence oyster 

 population dynamics and production 

 (Lenihan, 1999). Consequently, har- 

 vest-related reef destruction and degra- 

 dation are considered major factors that 

 have led to declines of American oys- 



