712 



Effects of harvesting methods on sustainability 

 of a bay scallop fishery: dredging uproots seagrass 

 and displaces recruits 



Melanie J. Bishop 



Charles H. Peterson 



Henry C Summerson 



David Gaskill 



University of North Carolina at Chapel Hill 



Institute of Marine Sciences 



3431 Arendell St 



Morehead City, North Carolina 28557 



E-mail address (for M J Bishop, contact author) melaniebishop-1fgiutsedu.au 



Present address (for M. J. Bishop): Department of Environmental science 



University of Technology, Sydney 

 Corner of Westbourne St. and Pacific Highway 

 Gore Hill, New South Wales, Australia 2065 



Fishing is widely recognized to have 

 profound effects on estuarine and 

 marine ecosystems (Hammer and 

 Jansson, 1993; Dayton et al., 1995). 

 Intense commercial and recreational 

 harvest of valuable species can result 

 in population collapses of target and 

 nontarget species (Botsford et al., 

 1997; Pauly et al., 1998; Collie et al. 

 2000; Jackson et al., 2001). Fishing 

 gear, such as trawls and dredges, that 

 are dragged over the seafloor inflict 

 damage to the benthic habitat ( Dayton 

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

 Jennings and Kaiser, 1998; Watling 

 and Norse, 1998). As the growing 

 human population, over-capitalization, 

 and increasing government subsidies 

 of fishing place increasing pressures 

 on marine resources (Myers, 1997), 

 a clear understanding of the mecha- 

 nisms by which fishing affects coastal 

 systems is required to craft sustain- 

 able fisheries management. 



Dredging, possibly the most de- 

 structive of common fishing meth- 

 ods (Collie et al., 2000), has been 

 the subject of many recent ecological 

 studies (Dayton et al., 1995; Jen- 

 nings and Kaiser, 1998; Thrush et 

 al., 1998). These studies indicate that 

 dredge extraction and disturbance 

 can have large direct effects on the 

 abundance, biomass, and diversity of 

 resident macrobenthic species (e.g., 

 Caddy, 1973; Eleftheriou and Robert- 



son, 1992). In addition, dredging can 

 indirectly affect macrobenthic species 

 through disturbance of benthic habi- 

 tat (Ramsay et al., 1998; Lenihan 

 and Peterson, 1998). Indirect impacts 

 of dredging may be particularly seri- 

 ous where highly structured biogenic 

 habitats, such as oyster reefs or sea- 

 grass beds, are affected (Peterson 

 et al., 1987; Lenihan and Peterson. 

 1998; Collie et al., 2000; Lenihan 

 and Peterson, 2004). These habitats 

 may be considered essential habitat 

 for many species of fish of commer- 

 cial or recreational value (Thayer 

 et al., 1975), providing refuges from 

 predators (Orth et al., 1984; Castel 

 et al., 1989) and abundant epibiotic 

 food (Virnstein et al., 1984; Sanchez- 

 Jerez et al., 1999). 



Among fishery species dependent 

 on biogenic habitat is the commer- 

 cially and recreationally important 

 bay scallop (Argopecten irradians). In 

 the two reproductive seasons, spring 

 and fall, bay scallop recruits settle 

 onto hard substrates (Belding, 1910; 

 Castagna, 1975) where they remain 

 attached for the first few months of 

 their lives. They then complete their 

 12-24 month life cycle on the estuary 

 floor. In North Carolina, eelgrass is 

 the only hard substrate of any abun- 

 dance to which bay scallop recruits 

 can attach themselves (Kirby-Smith, 

 1970). 



Commercial harvest of bay scallops 

 in North Carolina is achieved pri- 

 marily by toothless epibenthic dredge 

 (22.7 kg legal limit; NCFMC 1 ). Dredg- 

 es have the advantage that, unlike 

 rakes, they can be used from boats in 

 deep as well as shallow waters. Their 

 disadvantage is that they decrease 

 the biomass and shoot density of sea- 

 grass in scallop beds (Fonseca et al., 

 1984). Early in the North Carolina 

 scallop season, which extends from 

 December through May (NCMFC 1 ), 

 most of the juveniles from the previ- 

 ous fall spawning are still attached 

 to seagrass blades (Spitsbergen-). If 

 these juveniles are displaced by habi- 

 tat destruction, reduced numbers of 

 scallops may be available for harvest 

 in the subsequent year (hypothesized 

 by Thayer and Stuart. 1974). Al- 

 though seagrasses can recover from 

 small-scale disturbances to shoots by 

 vegetative growth, large-scale dis- 

 turbances to their subsurface root 

 and rhizome system may permanent- 

 ly reduce the density of submerged 

 aquatic vegetation (SAV) (Peterson 

 et al., 1987) such that it may limit 

 settlement of the following year's 

 recruits or induce greater rates of 

 predation on them (or bring about 

 both). Although, in North Carolina, 

 the bay scallop fishery management 

 plan requires that the scallop sea- 

 son be opened after fall spawning is 

 completed (Peterson, 1990); it fails 

 to consider how methods of harvest 

 may indirectly effect spawning stock 

 biomass in years to come. 



1 NCMFC (North Carolina Marine Fisher- 

 ies Commission). 2005. North Caro- 

 lina fisheries rules for coastal waters, 

 210 p. North Carolina Department of 

 Environment and Natural Resources, 

 1601 Mail Service Center, Raleigh, NC 

 27699. 



2 Spitsbergen, D. 1979. A study of the 

 bay scallop (Argopeeten irradians) in 

 North Carolina waters. Report for Proj- 

 ect 2-256-R, 44 p. North Carolina Divi- 

 sion of Marine Fisheries. 3441 Arendell 

 Street, Morehead City, NC 28557 



Manuscript submitted 30 October 2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 1 April 2005 by the Scientific Editor. 



Fish. Bull. 103:712-71912005). 



