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Nonnative Oysters in the Chesapeake Bay 6 History and Current Status of Restoring Native Oysters Reefs in the Chesapeake Bay INTRODUCTION The potential for restoring the Eastern oyster, Crassostrea virginica, on oyster reefs to self-sustaining populations appears to be one of the critical issues in restoring the overall integrity and functionality of the Chesapeake Bay ecosystem. Since oyster reefs are an essential component in the estuarine ecology of the bay, restoring reefs to functioning levels is a multifaceted priority for many resource managers. Both Virginia and Maryland have a long history of oyster restoration, and recent restoration strategies are based on information gained over many decades of restoration management (see Box 6.1). Oyster resource management programs have historically been directed toward maintaining a sustainable oyster fishery and producing fishery-dependent revenues. Only recently has there been a shift in management objectives toward rehabilitation of impaired resources and habitat to restore ecological function. Oysters have long been recognized as a keystone species in the bay, and there is growing awareness of the role productive oyster reefs play in providing vital ecological and economic benefits other than fisheries alone. Currently, more emphasis is being placed on the ecological benefits of functioning oyster reefs in estuarine ecosystems, including values related to filtering capacity, structural fishery habitat, species diversity, and trophic dynamics. However, it is also important to understand that restoring productive oyster reef habitat is only one part of a complex problem, and resource managers and researchers must guard against the sentiment that oyster restoration can singularly resolve all of the ecological and environmental problems facing the bay. Successful oyster
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Nonnative Oysters in the Chesapeake Bay BOX 6.1 Chronology of Oyster Restoration Management in the Chesapeake Bay 1914 First experiments with transplanting oyster seed in Maryland 1921 First experimental shell-planting project in Maryland 1922 Maryland initiates shell-planting program 1927 Watermen’s Advisory Committee formed in Maryland 1927 Maryland dedicates funding for shell-planting/oyster rehabilitation program 1928 Virginia initiates shell-planting program 1943 Maryland Board of Natural Resources is created 1943 Maryland BNR Oyster Management Plan developed (seed areas and seed planting) 1960 Maryland initiates oyster repletion program 1960 Maryland initiates shell-dredging program (fossil shell) 1961 Department of Tidewater Fisheries is given authority over natural oyster reefs 1963 Potomac River Fisheries Commission is established 1969 Maryland Department of Natural Resources is created by legislation 1988 Virginia convenes Blue Ribbon Oyster Panel 1989 Chesapeake Bay Oyster Management Plan 1990 Oyster Disease Research Program is established (NOAA/Sea Grant) 1991 Maryland establishes surcharge to fund repletion program 1992 Virginia’s Blue Ribbon Oyster Panel reports recommendations to VMRC 1993 Virginia uses selected hatchery-reared larvae (disease resistance) 1993 Maryland convenes Oyster Roundtable 1993 Maryland develops the Oyster Roundtable Action Plan 1993 Chesapeake Bay Policy for Introducing Nonindigenous Aquatic Species 1994 Maryland initiates hatchery production of larvae 1994 Chesapeake Bay Oyster Management Plan is revised 1994 Chesapeake Bay Aquatic Reef Habitat Plan is adopted 1994 Maryland Oyster Recovery Partnership (broad partnership) 1999 Virginia Oyster Heritage Program (broad program goals and participants, funding) 2000 Chesapeake 2000 Agreement is developed 2002 Draft Comprehensive Oyster Management Plan SOURCE: Modified from Tarnowski, 1999. reef restoration and the recovery of oyster resources does not directly equate with the overall recovery of Chesapeake Bay, but successful oyster reef restoration is a major component of returning the ecosystem to a more productive condition and should be linked with other ongoing efforts to improve conditions in the bay. Current programs to restore native oyster populations seek to identify successful management strategies and measure performance in terms of functionality. The oyster industry has long held that successful restoration could be measured by increased harvests, a perspective that has influenced fishery management policies for decades. Although increased economic benefit derived from increased landings is a legitimate measure
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Nonnative Oysters in the Chesapeake Bay of success, it is not the only criterion for measuring success. Recent research and management practices have also emphasized measuring success by evaluating ecological benefits. The importance of restoring oyster reefs to functional levels is also a central element in the argument about whether to continue restoration efforts with the native oyster or with a surrogate nonnative oyster. The underlying question is whether the native oyster or a surrogate oyster provides the greatest potential for restoring ecological functionality and stability to the bay. Research and management programs in Virginia and Maryland and neighboring states have provided substantial multidisciplinary information about the potential restoration of C. virginica. On the other hand, very little is known about the restoration potential of nonnative oysters, especially C. ariakensis. Researchers at the Virginia Institute of Marine Science (VIMS) in cooperation with the Virginia Seafood Council conducted investigations to determine the feasibility and potential of using a nonnative species for open-water aquaculture. The results of these investigations suggest that the Suminoe oyster, C. ariakensis, is a promising surrogate for the native oyster. Virginia’s oyster industry, via the Virginia Seafood Council, has expressed the opinion that past efforts to restore C. virginica have generally met with failure and that the future of the industry depends on introducing C. ariakensis as quickly as possible. A different opinion is held by some of the partners involved in the Chesapeake Bay Program, who recommend continuation of oyster restoration with the native oyster and have expressed concerns that directing funds and efforts away from current restoration programs will be counterproductive. Recent restoration efforts combine coordinated actions by state, federal, and private organizations under the mandates of Chesapeake Bay 2000 to restore and maintain the valuable ecological services provided by native oyster populations while continuing to support local oyster fishing interests. The following information represents a cursory review of the history of oyster restoration efforts in the Chesapeake Bay to identify the benefits and shortcomings of these programs and to evaluate the potential of future restoration programs. Need for Restoration Throughout the last century researchers and resource managers have provided a consensus regarding the depletion of oyster resources in the Chesapeake Bay. Foremost among the causes has been overfishing, a problem first recognized at the turn of the 20th century that has continued to the present (Hargis and Haven, 1999; Rothschild et al., 1994). Concomitantly, overfishing has led to the loss of oyster habitat.
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Nonnative Oysters in the Chesapeake Bay Rothschild et al. (1994) showed that oyster bar acreage in Maryland waters declined by more than 50% from 1907 to 1982, and the quality of existing oyster bars has been diminished to the point where population dynamics, productivity, and yields per habitable acre are substantially reduced. Various methods of harvesting, primarily mechanical harvesting devices, used over the long term have destroyed the structural integrity of oyster reefs and depleted available substrate that is suitable for larval settlement. Rothschild et al. concluded that the effects of fishing manifested through modification of oyster reefs had a much greater influence on the long-term decline of the oyster than degraded water quality and the effects of diseases. It is important to note that the conclusions of Rothschild et al. focused on habitat destruction prior to the period when extensive oyster mortalities were associated with diseases. Since the 1990s, diseases caused by two protist parasites, Haplosporidium nelsoni (MSX) and Perkinsus marinus (Dermo), have substantially increased mortality rates among older oysters, contributing to decreased harvests and reproductive potential. Additionally, environmental disturbances affect oyster reproduction and survival. Mining shell from extant and extinct reefs has substantially reduced reef structure and elevations to levels where recolonization has been unsuccessful. Diminished water quality, resulting from numerous human activities, has adversely affected overall estuarine habitat and environmental health. Eutrophication from excessive nutrient inputs and different types of contaminants and riverine sediment loads have combined to adversely affect growing waters where oysters can survive and reproduce. It is clear from the history of management in both Virginia and Maryland that poor management decisions, legislation, and failure to react to available scientific information have contributed to resource management problems. Historically, most management efforts were directed at sustaining the oyster industry as opposed to restoring oyster populations over the long term (Haven et al., 1981; Kennedy and Breisch, 1983; Rothschild et al., 1994; Tarnowski, 1999; Hargis and Haven, 1999). Numerous researchers and managers have pointed out that many resource management decisions were based on fishery-driven objectives and that the decision-making process was influenced by social and political interests instead of scientific data (Haven et al., 1981; Kennedy and Breisch, 1983; Rothschild et al., 1994; Tarnowski, 1999; Hargis and Haven, 1999). Rothschild et al. (1994) suggested that the effects of a diminished oyster population must have changed the ecology of the bay and that the effects should have become evident at the time of maximum stock declines (from 1884 to 1910). More recently, the complex ecological commu-
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Nonnative Oysters in the Chesapeake Bay nity associated with oyster reefs has gained more attention, and developing functional ecological relationships has become the focus for restoration efforts. Science plays a major role in the decision-making process, as resource managers take a holistic approach to oyster management. Resource managers have now agreed on a more comprehensive approach to oyster resource management and oyster restoration. The holistic approach includes coordinated multifaceted management strategies to restore oyster populations to self-sustaining levels, to provide ecologically valuable reef habitat, to improve ecological services such as water quality, and to provide an economic benefit for resource users. Rothschild et al. (1994) proposed a four-point strategy to effect recovery of Maryland’s oyster resources and to revitalize the oyster fishery involving fishery management, repletion, habitat replacement, and broodstock sanctuaries. Similarly, Hargis and Haven (1999) listed four purposes for restoration other than increasing harvests of seed and market oysters: restoration of broodstock levels, genetic enhancement by allowing for natural selection, restoring the biological and ecological functions of oyster reefs (filtration), and restoring the oyster reef-associated community structure. In combination these elements provide broad benefits from restoration, serve multiple purposes and user groups, and allow for sharing costs among multiple objectives. Mann (2000) posed several questions regarding oyster restoration in the Chesapeake Bay, including whether revitalization of the oyster fishery should be the prime motivation for restoration of oyster populations. He further asked if restoration of the resource should optimize harvest and economic return or should restoration optimize ecological complexity and stability. Both strategies provide important fishery restoration goals and positive societal benefits but are influenced by biology, economics, perception, and time. The question remains whether both the economic benefits related to the oyster fishery and the ecological benefits related to productive self-sustaining oyster populations can be generated concomitantly from future resource restoration programs (Chesapeake Research Consortium, 1999). In the near term, restoration efforts intended to support fishery harvests are incompatible with restoration efforts intended to renew ecological functionality. Similarly, restoration efforts focused on ecological objectives are unlikely to ensure economic viability of the fishery. In the long term, restoration of ecological functionality could provide harvestable surplus sufficient to meet fishery needs. Coen and Luckenbach (2000) have proposed that ecologically motivated restoration of oyster reef habitat will be a growing practice and that the challenge is to identify their ecological benefits. In the broadest sense the goals of restoring oyster reef habitat are maintenance of biodiversity, increased finfish and shellfish
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Nonnative Oysters in the Chesapeake Bay production, and improved ecosystem function (Coen and Luckenbach, 2000). HISTORY OF OYSTER RESTORATION IN THE CHESAPEAKE BAY Restoration of oyster reefs as a practicable resource management strategy has been used in many oyster-producing regions for more than a century. Oyster fishery management in the Chesapeake Bay can be traced back as early as the 1880s when the Baylor Survey was initiated to delineate public oyster grounds (Haven et al., 1981). Oyster resource management in the Chesapeake Bay has been described by Haven et al. (1978, 1981), Hargis and Haven (1988, 1999), and Wesson et al. (1999). Numerous researchers have also reported the precipitous decline in oyster production and provided management guidelines for protecting, conserving, and maintaining oyster stocks and habitat in the bay (Haven et al., 1978, 1981). The complex nature of oyster resource restoration has been described by Kennedy and Breisch (1981), Haven et al. (1981), Bartol and Mann (1997), Southworth and Mann (1998), and Mann (2000). Hargis and Haven (1999) have listed the ecological conditions under which oyster reefs originate and survive and applied them in developing a list of guidelines to plan and conduct reef restoration projects. Virginia Virginia’s public reef shell-planting program began in 1928 (Hargis and Haven, 1999) when repletion taxes were enacted to set aside monies to fund public oyster repletion programs. Repletion programs (in 1928, 1952, and 1961) were supported by funds generated by state and federal sources but were largely financed by state subsidy and were not self-supporting (Haven et al., 1981). Haven et al. provided an overview of Virginia’s oyster repletion program carried out by the Virginia Marine Resources Commission (VMRC) but added that the efforts of the state had not succeeded in reversing the downward trend in oyster production from public grounds or private leases. Harvest reduction was attributed by loss of habitat through many activities (harvesting and shell mining), sedimentation, predation, disease, and poor water quality (Hargis and Haven, 1999). Haven et al. (1981) included a list of major public management problems facing the repletion program. Poor recruitment of oysters in the James River seed area was identified as a major factor contributing to declines in oyster production. This seed area was one of the principal sources of seed oysters for the private sector growing oysters on leased bottoms prior to 1960. Private growers resorted to importing seed oysters from neighboring states for planting on their leases.
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Nonnative Oysters in the Chesapeake Bay Haven et al. reported that without a reliable source of seed stocks the oyster farming industry would continue to face difficult times and ultimately cease to exist in its present form. In response to declining production, Haven et al. summarized methods to improve growing oysters, and emphasized enhancing natural production. Among the most promising management approaches was depositing reef shell or processed oyster shell on public grounds and private leases to create favorable substrate for larval settlement. Early replenishment programs in Virginia focused primarily on watermen transplanting seed oysters to enhance harvests (Wesson et al., 1999). Transplanting seed stocks is a complicated practice, with seed being generally moved from high-salinity areas to low-salinity areas. This practice takes advantage of heavier spatfall in high-salinity areas and lower disease prevalence and intensity in lower-salinity areas. In 1994 and 1995 the replenishment program in Virginia received two oyster disease research grants to develop and test protocols that take advantage of higher salinity for setting while reducing the impacts of oyster diseases (Wesson et al., 1999). Until the mid-1990s almost all shell-planting efforts were directed toward the practice of creating new oyster reefs rather than maintaining existing natural oyster reefs. In 1993 the replenishment program began concentrating restoration efforts on existing reefs that appeared to have favorable contours, but where substrates were depleted of shell and live oysters. The VMRC’s Shellfish Replenishment Program initiated a reef-based restoration effort in the Piankatank River in 1993 (Bartol and Mann, 1997), and a contrasting approach was employed in the Great Wicomico River in 1996 (Southworth and Mann, 1998). Initial shell planting on seed-producing grounds of the James River proved successful by doubling the natural spat set on almost all areas that were subjected to shell application (Wesson et al., 1999). A second study of natural reefs indicated that many had been harvested to such an extent that reef elevations were below optimal elevations for recruitment and survival. The practice of creating new oyster bars in areas that did not historically support oyster reefs was shown to be more expensive and less effective than enhancing natural reefs and taking advantage of existing reef elevations in areas where oysters had previously occurred. Reduction in reef elevations was seen as a serious problem, and any large-scale reef restoration requiring substantial reconstruction would be very expensive. Wesson et al. (1999) reported that, when reef elevations are too low, restoration will be unsuccessful unless the entire reef elevation is raised. The Virginia Blue Ribbon Oyster Panel’s plan for managing oysters was adopted in 1992 as a guide to oyster restoration over the next 10 years. The goals of the plan were to achieve no net loss of existing stand-
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Nonnative Oysters in the Chesapeake Bay ing stocks of oysters over the next 5 years and to achieve a doubling of existing standing stocks of the native oyster over the next 10 years. In 1994 the Chesapeake Bay Aquatic Reef Plan and the Oyster Fishery Management Plan also specified oyster restoration as a management practice. The Chesapeake Bay Program designated approximately 5,000 acres each in Maryland and Virginia and 1,000 acres in the Potomac River to create new oyster habitat by 2000. Progress toward these goals was made through several projects, including direct application of cultch to improve substrates and facilitate settlement and recruitment, reef enhancement using dredged fossil shell (buried shell), and the construction of elevated reef structures in Virginia’s subestuaries of the Chesapeake Bay (Wesson et al., 1999). Since 1999 the Virginia Oyster Heritage Program has provided the framework for broader participation in reef restoration projects. The program was established as a fund-raising program, but it also provides public relations and educational components. This program funded a 3-year project that included construction, management, and monitoring of restored oyster reefs in sanctuaries and public grounds. Most recently, the Chesapeake 2000 Agreement (see Appendix E) established oyster restoration goals to increase native oyster populations in the bay by a minimum of 10-fold by 2010 and to develop and implement a strategy to achieve this increase by using sanctuaries sufficient in size and distribution, aquaculture, continued disease research and disease-resistant management strategies, and other approaches to restore native oyster productivity to the bay. The baseline for this goal was the estimated biomass of oysters at the beginning of 1994. An important element in establishing the oyster restoration goal is recognition that the native oyster is a keystone species and that oyster reef communities are essential components in the ecology of the bay. The cost of achieving this goal was estimated at $100 million. It has been calculated that 1,500 acres in the bay need to be restored by 2010 to reach the Chesapeake 2000 Agreement’s goal of a 10-fold increase in oyster biomass. Maryland Kennedy and Breisch (1981) provide a comprehensive review of oyster research and resource management. Tarnowski (1999) presents a chronology of factors affecting oyster resource management in Maryland. From a historical perspective, oyster resource management dates back more than a century and restoration efforts to about 1921, when the state funded projects to replace processed shell to rehabilitate oyster reefs. Maryland initiated an annual funding mechanism in 1927 to provide a more reliable means of financing the seed- and shell-planting program.
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Nonnative Oysters in the Chesapeake Bay By 1932 about a million bushels of oyster shell (cultch) were planted on natural reefs. These early restoration efforts, however, did not succeed in improving oyster harvests. In 1935 the state planning commission noted that depletion of the oyster resource could be traced to overfishing, exploitation of seed stocks, and a failure to return adequate supplies of cultch to the bay, which consequently resulted in a decline in oyster harvests and the demise of the oyster canning industry. In response to declining harvests, the commission made several recommendations, including developing seed areas, transplanting seed to public reefs, planting cultch on suitable reefs, amending leasing laws, and increasing potential lease areas. The commission also recommended that every shell taken from Maryland waters be returned as cultch for restoration. In 1942 the Tidewater Fisheries Commission undertook a large seed-growing and seed-transplanting operation based on a tax on oysters taken from the grounds. The Board of Natural Resources was created in 1943 and defined a program for oyster management, including seed and shell planting, area rotation and closures, encouraging private leasing, and a bushel tax to help fund the program. Shell taxes on shucked oysters were enacted in 1947 and 1951 to support shell-planting programs, and in 1953 laws were enacted that allowed the state to collect 50% of all shells produced. Even with this law in place, shell collections were not sufficient to provide adequate quantities of processed shell for cultch, and efforts were made to identify sources for dredged shell (Kennedy and Breisch, 1981). Maryland has been operating a large-scale dredging and shellplanting project, as part of its oyster repletion program, since about 1960 (Kennedy and Breisch, 1981; Rothschild et al., 1994; Tarnowski, 1999). In the early 1960s, large deposits of fossil shell were dredged from non-producing grounds and deposited on public reefs to supplement the shell-planting program. During the 1960s, cultch plantings increased five-fold, which, combined with good spat sets, resulted in the highest harvests in decades (Tarnowski, 1999). During the 1960s and 1970s the state contracted for the dredging, washing, and replanting of about 5 million bushels a year, about 80% of the shell planted for seed production. These quantities far exceeded the amount of fresh shell that was made available during this period (Kennedy and Breisch, 1981). Possibly in response to the supplies of dredged shell, laws were amended that reduced the percentage of fresh shell that processors were required to make available to the state. The oyster fishery appeared to be moving in a positive direction during the 1970s when a series of natural events sent the industry into a tailspin from which it has yet to recover. Poor spat sets, due to prolonged low salinities, contributed to widespread production declines (Tarnowski, 1999). Since the shell-planting program expanded in the 1960s, approximately 180 million bushels of shells have been planted to
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Nonnative Oysters in the Chesapeake Bay restore reefs in Maryland waters (C. Judy, Maryland Department of Natural Resources, Annapolis, personal communication, 2002). After 40 years of dredging, sources of fossil shell are nearly exhausted. Oyster management practices in Maryland were primarily directed toward maintaining the fishery instead of restoring the functionality of oyster reefs. Management activity was dedicated to transplanting seed to augment fisheries production by moving seed oysters from seed reefs where recruitment occurred to other public reefs where recruitment was limited. The political realities of the management community required the State to provide harvestable oysters to maintain the public oyster industry (Paynter, 1999). The Oyster Management Plan, developed in 1989 and revised in 1994, provided a more comprehensive management approach. The plan recommended developing and initiating short- and longterm management actions to help stabilize harvests, maintain spawning stocks, promote conservation goals, and develop seed stock sources. Rothschild et al. (1994) provided a four-point strategy to revitalize Maryland’s oyster fishery: fishery management, repletion, habitat replacement, and broodstock sanctuaries. The repletion strategy involved the deposition of mined fossil shell to provide a substrate to increase recruitment and subsequently transplanting recruited spat into areas to improve growth and survival. The habitat replacement strategy involved creating new substrate to enhance recruitment, growth, and survival with the objective of long-term oyster recovery. The broodstock sanctuary strategy would include harvest restrictions and would amplify the positive attributes of the fishery management, repletion, and habitat replacement strategies. Maryland’s oyster production during the mid-1990s continued to rely on seed movement programs that transplanted 1-year-old juvenile oysters from moderate-salinity areas (southern regions) to more brackish waters (northern region). This management practice was based on the observation that oysters growing in high- and moderate-salinity areas are not expected to survive their second summer and will not grow to market size in the presence of severe P. marinus infections. Since the parasite occurs at high prevalence and intensity among oysters growing in higher-salinity waters of the bay, the adverse impacts of disease were reduced by establishing seed reefs in areas where recruitment is high and survival is low and then moving seed to supplement areas where recruitment is low but survival is higher. Some projects have proven to be successful and some have not, and success has been variable from region to region (Paynter, 1999). Another key issue is the loss of brood stock and recruitment potential resulting from the transfers to the upper part of Chesapeake Bay, where the larval survival rate is drastically reduced by environmental conditions (temperature-salinity combination).
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Nonnative Oysters in the Chesapeake Bay While the repletion program has contributed to maintaining, to some degree, harvests and the watermen’s way of life, there are several important drawbacks to the program. Foremost, transplanting infected oysters provides a potential pathway to introduce pathogens to growing areas where they might not normally occur (Paynter, 1999). In 1993, Maryland convened the Oyster Roundtable with the goal of developing sound, broadly supported recommendations for reviving oyster populations in the bay. Specific objectives included maximizing and enhancing ecological benefits, maximizing and enhancing economic benefits derived from harvest from public and private oyster grounds, and maximizing the ability of government to respond effectively to the magnitude of the problem. The Maryland Oyster Roundtable Action Plan developed action items concerning five general issues related to oyster production and ecology: diseases affecting oyster production, habitat and water quality, production and management, institutional barriers, and funding (Paynter, 1999). Subsequently, repletion programs developed annual work plans based on the Maryland Fall Dredge Survey, site surveys, and fisheries management criteria. The annual work plan follows the guidelines established by the action plan and is reviewed by the Oyster Roundtable Steering Committee. Paynter (1999) provides a detailed summary of the Maryland Oyster Roundtable Action Plan, including addressing issues directly related to restoring oyster production, restoring oyster habitat, and the repletion program. Restoration activities included large-scale construction and seeding programs, restricting harvests, and monitoring. There was continued support for the repletion program, since the bulk of the oysters harvested resulted from those activities. The concept of oyster recovery areas was developed to set aside areas in the bay where shellfish harvesting and planting are restricted and carefully controlled. These sanctuaries, where harvest is prohibited, were established to provide greater control over the potential movement of diseases, to maximize the reproductive potential of brood stocks, to provide an opportunity to evaluate different aquaculture methods, and to set aside areas where controlled research could be conducted (Paynter, 1999). The Maryland Department of Natural Resources is currently managing 24 sanctuaries throughout the bay, ranging in size from 5 to over 5,800 acres. It also restores managed areas called reserves, which are closed to harvests initially but may be opened for managed harvests when adequate stocks are present. In 1994 the Chesapeake Bay Aquatic Reef Plan specified oyster restoration as a management practice. The Chesapeake Bay Program designated approximately 5,000 acres in Maryland to create new oyster habitat
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Nonnative Oysters in the Chesapeake Bay FIGURE 6.1 Virginia expenditures on oyster restoration and oyster landings. SOURCE: Data from J. Wesson, VMRC, Newport News, personal communication, 2003. support a self-sustaining oyster population. More specifically, the restored habitat should provide three-dimensional substrate in locations where recruitment and water quality support the growth and development of oysters. Similarly, Mann (2000) recognized several factors that will facilitate restoration, including developing high-density, three-dimensional reef structures in areas with favorable water quality; selecting sites where positive impacts are visible in a short time frame; and concentrating efforts on a river system basis rather than attempting wholesale restoration across the bay. Hargis and Haven (1999) recommended that restoration of the seed area in the James River estuary be a priority but did not discourage restoration efforts in other historical oyster-producing river estuaries. Mann (2000) suggested that the problem for proponents of reef restoration is not so much demonstration of biological recruitment in the field as social and political recruitment of citizens to support such efforts on a long-term basis. Successful restoration efforts provide a vehicle to educate the public and foster vested interest groups. Likewise, Coen and Luckenbach (2000) suggested that the most critical element in establishing meaningful success criteria was achieving a proper balance of
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Nonnative Oysters in the Chesapeake Bay FIGURE 6.2 Annual funding of Maryland oyster projects versus harvest. SOURCE: Data from C. Judy, Maryland Department of Natural Resources, Annapolis, personal communication, 2003. sociopolitical constraints and ecological objectives. Balancing short-term fishery-driven interest with the need to establish long-term sustainable, ecologically functional oyster reefs poses a formidable resource management challenge. Since oyster reefs and oyster populations are essential elements in the estuarine ecosystem, oyster restoration should be viewed as a component in a holistic approach to applied resource management. In a holistic approach, oyster restoration efforts must be combined with numerous multifaceted resource management and development options that will contribute to successful reestablishment of productive oyster grounds. In this approach the economic benefits derived from oyster harvests may be only a secondary benefit. Alternative Hatchery-Based Management Strategies The restoration of oyster reefs may include an aquaculture component when hatchery-reared larvae and spat are used to seed reefs and supplement natural recruitment. Stocking programs using hatcheryreared stocks may become important for “jump-starting” oyster popu-
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Nonnative Oysters in the Chesapeake Bay lations on newly constructed or depopulated reefs (Allen and Hilbish, 2000). The use of hatchery-reared stocks for restoration will require careful selection of brood stocks that may be chosen for specific applications and genetic characteristics. Additionally, hatchery practices must be established to ensure that selective breeding programs are operated to maintain genetic variability among extant populations. Stocking programs that use hatchery-reared larvae and spat increase the risk of diluting natural population variation. Inevitably, the widespread use of selected hatchery-reared seed stocks will favor genetic transfer among extant stocks as interbreeding takes place among natural and/or hatchery-reared stocks. Changes in genetic diversity may have long-term impacts on postrestoration populations, if extant populations become increasingly inbred. Conversely, genetic improvements in hatchery-reared stocks may be swamped by inbreeding within postrestoration stocks, possibly with no recognizable benefits from selective breeding to extant populations (Ryman and Laikre, 1991). The actual genetic impact of selective breeding on restoration programs will depend on three parameters: the magnitude of augmentation, the effective size of the hatchery contribution, and the effective size of the recipient population. This information is essential to understanding the risks and potential consequences of using selective-bred, hatcheryreared seed stocks to augment natural populations (U.S. Department of Commerce, 2002). Avoiding the presence of pathogens and alternatively using pathogen-free seed stocks have been identified as a critical element in restoration. Management could include the use of disease-resistant seed to infuse (interbreeding) selected genetic traits (alleles) and provide inheritable and sustainable disease resistance across an oyster population (Allen and Hilbish, 2000). Both Virginia and Maryland have established programs using hatchery-reared seed to evaluate disease resistant strains of C. virginica. The Aquaculture Genetics and Breeding Technology Center is testing disease-resistant strains to develop selected strains that are resistant to MSX and Dermo diseases and that can be ultimately used to produce disease-resistant seed for restoring oyster populations. Maryland and Virginia also participate in the Cooperative Regional Oyster Selective Breeding Project (CROSBreed) to develop dual-disease-resistant C. virginica capable of restoring dehabilitated populations. Results from the selective breeding project suggest that selected strains slow the development of lethal infections and demonstrate increased survival rates and longevity, as discussed in Chapter 4. Genetic transfer from selected parental stocks to natural oyster populations (genetic rehabilitation) may also be an objective, particularly where disease is a major threat to population recovery. The desired outcome of
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Nonnative Oysters in the Chesapeake Bay interbreeding is hybridization favoring introgression of disease-resistant alleles into the natural population (Allen and Hilbish, 2000). To evaluate the effects of interbreeding and genetic transfer, disease-resistant seed should be stocked in closed/retentive systems (rivers, trap estuaries) where auto-recruitment rates are expected to be high. Interbred progeny can be monitored to determine introgression rates and production parameters (Allen and Hilbish, 2000). When an intensive (highly controlled) aquaculture component is introduced into the management strategy, the question of cost emerges. Reef restoration programs, based on hatchery-reared seed, may be severely limited by problems of scale and economic limitations. It is widely recognized that the levels of hatchery production today are generally an order of magnitude or two too low to effectively provide the numbers of seed stocks needed to achieve restoration goals (Allen and Hilbish, 2000). While restoration efforts have resulted in limited progress in establishing sustainable oyster populations, there remains an opinion among some researchers and resource managers that a more comprehensive management approach will ultimately lead to some level of oyster resource recovery. The approach would rely on applying a more stringent genetic improvement component based on newly emerging technologies, developing disease-resistant strains; selecting locations where environmental conditions are favorable for recruitment, growth, and survival; designing and constructing optimal reef habitat to encourage spat setting; avoiding disease, including growing oysters in areas or in a manner that reduces the chance of infection and not using infected seed; managing postrestoration populations for multiyear class distributions; and setting a long-term time frame (decade) for success (multigenerational approach to genetic introgression and auto-recruitment). Draft Comprehensive Oyster Management Plan The Comprehensive Oyster Management Plan (COMP) was developed by representatives from state and federal agencies, academia, environmental organizations, and the oyster industry through the Chesapeake Bay Program. The COMP provides both the general framework and specific guidance for implementing a strategic, coordinated, multipartner effort to restore and manage native oyster populations in the Chesapeake Bay (Chesapeake Bay Program, 2002). The main strategies presented in the COMP are managing around disease, establishing sanctuaries, rebuilding habitat, increasing hatchery production, managing harvest, improving coordination among partners, and developing a database to track
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Nonnative Oysters in the Chesapeake Bay projects. Sanctuaries are one of the main strategies for managing recovery by regulating the oyster fishery; special management areas (reserves) will be established to provide control over harvesting. The COMP also recognized the importance of using the Maryland Priority Restoration Areas or the Virginia Oyster Restoration Plan for identifying suitable sites for sanctuaries and other restoration activities. The COMP recognizes the major impediments to rebuilding oyster resources (diseases and habitat condition) and acknowledges that restoration will require a multigeneration, long-term effort, without guarantees that the objectives will be met. The plan’s objectives include: increase oyster populations to levels that restore important ecological functions, habitat, and self-sustaining regional populations; achieve a sustainable oyster fishery through a combination of harvest from public oyster grounds and private aquaculture; reduce the impacts of disease on oyster populations; and increase hatchery production and develop disease-resistant strains. POTENTIAL CONSTRAINTS TO LONG-TERM RESTORATION PROJECTS Funding Estimated costs of achieving the Chesapeake 2000 Agreement’s goal of a 10-fold increase is $100 million over the next 10 years. It is expected that the federal government will contribute about 50% of the funds to achieve this goal through projects supported by the ACOE, the Environmental Protection Agency, and National Oceanic and Atmospheric Administration (Chesapeake Bay Program, 2000). The states and participating partnerships will have to generate the remaining funds. Funding for oyster restoration projects in Virginia has increased from about $1 million in 1999 to $4.5 million in 2002, and the annual projected cost is about $3.1 million. Maryland currently spends about $1 million a year on its oyster repletion projects but has committed to spending $25 million over the next 10 years. Maryland’s projected funding for 2003 includes $3.552 million for fishery restoration projects and $2.458 million for sanctuary restoration projects. Because substantial increases in state spending are necessary to support the projects proposed in the Chesapeake 2000 Agreement, there is concern among state resource managers that funding for restoration projects may be more difficult to obtain, especially during times when state budgets are facing increased demands and de-
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Nonnative Oysters in the Chesapeake Bay creased revenues. In addition, if short-term outcomes fail to demonstrate success in terms important to stakeholders, political support for restoration efforts could diminish. Time It will take decades and possibly centuries to restore native oyster populations and oyster reefs. The time frames presented in the Chesapeake 2000 Agreement appear ambitious and probably naïve. There may be pressure to demonstrate success over the short term. Political support, partnerships, and funding may be closely linked to perceived success and may diminish when project goals are extended over decades. The question of who will benefit from the success of long-term projects may diminish current commitments and partition supporters. Clearly, the oyster industry seeks immediate relief and declares that the industry will not survive under a long-term recovery strategy. Continuous Epizootics The biggest challenge to oyster restoration in the Chesapeake Bay is overcoming mortalities associated with diseases. Changing seasonal, climatic, and environmental conditions make it difficult to manage oyster stocks in the presence of disease. Environmental conditions, especially temperature and salinity, affect the distribution and abundance (prevalence and intensity of infection) of parasites. Currently, P. marinus occurs among all productive oyster populations in the bay. The approach includes managing for diseases by avoiding disease in project site selection, planning, prereef development preparation, and habitat rehabilitation. Disease management strategies may include efforts to clear reefs of infected oysters prior to replanting in an attempt to limit the use and distribution of infected stocks (seed and adults), avoiding waters and reefs where disease is likely to occur, and using specific pathogen-free seed. These strategies may reduce the impacts of disease and increase survival, but the challenge is to extend site-specific effects to a baywide scale (Chesapeake Bay Program, 2002). Baywide Recovery (10-fold Increase in Biomass) It has been estimated that 1,500 acres of productive oyster habitat need to be restored to achieve a 10-fold increase in oyster populations. The sanctuary concept is the structural basis for restoration and will require about 10% of the bay’s historically productive grounds. It appears that initial success may be attained on a regional or tributary-specific
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Nonnative Oysters in the Chesapeake Bay basis where specific management strategies can be applied to overcome specific challenges—that is, seeking optimal salinity regimes to avoid diseases, achieving spawning stock biomass sufficient to sustain reproductive potential, and retaining larvae in trap estuaries. However, restocking may become an integral component in sustaining these populations, since recruitment may be unpredictable. Optimal salinity zones (lower salinity where the impact of disease is reduced or higher salinity where recruitment is more successful) fluctuate, making management difficult. In Virginia, reliance on broodstock sanctuaries may not be sufficient for establishing stable, multiyear class oyster populations. There are few locations with favorable salinity regimes, and fluctuation in the location of optimal salinity zones (lower salinity where the impact of disease is reduced or higher salinity where recruitment is more successful) makes it more difficult to choose stable sites for sanctuaries. Self-Sustaining Oyster Populations Poor recruitment and the absence of multiple-year classes are recognized as obstacles to establishing self-sustaining oyster populations in many once-productive parts of the bay. Eliminating harvests, enhancing substrates, and controlling habitat degradation are potential management strategies to increase oyster populations, population size distributions, reproductive potential, spawning, and recruitment. The draft COMP incorporates restoration components that establish management areas to protect extant brood stocks by prohibiting or restricting harvesting. Oyster sanctuaries can be established to protect adult oysters, thereby protecting spawning stocks and contributing directly to the reproductive potential of the population. The concept of managed areas can also be expanded to include special managed areas and harvest reserves where oyster resources can be designated for harvest based on specific harvest criteria. Managing both sanctuaries and reserves according to specific management practices is expected to enhance reproductive potential and increase recruitment, contributing to self-sustaining oyster populations. However, the dilemma still exists when faced with the challenge of managing for sustainability under changing environmental conditions. During periods of lower salinity, oysters demonstrate a greater capacity to overcome the adverse effects of disease, but spat setting and recruitment are at best unpredictable and at worst nonexistent. During periods of higher salinity, spat setting and recruitment improve, but survival to reproductive age is markedly reduced. Restored oyster reefs may be subject to both extreme conditions for extended periods over several years, thus negating previous progress toward self-sustainability.
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Nonnative Oysters in the Chesapeake Bay Hatchery Production Restoration projects, especially in areas where recruitment is low, may become increasingly dependent on selected hatchery-reared seed stocks to maintain year classes and diverse population dynamics. This management strategy may rely on continuous seed input over an extended period. In situations where genetic introgression and auto recruitment are successful, long-term reliance on hatchery-reared seed stocks may become counterproductive by increasing the potential for adverse consequences associated with inbreeding and result in diminished genetic diversity among postrestoration populations. Current hatchery production cannot substitute for natural recruitment, except in limited site-specific restoration efforts. Hatchery production will have to be substantially increased to meet the demand for a 10-fold increase in oyster populations. However, incorporating an intensive aquaculture component (hatchery and nursery systems) into the restoration strategy will require increased funding. Sources of Shell for Reef Construction Known sources of shell for cultch are limited and may or may not be sufficient for large, long-term reef restoration projects. The dominant source of shells for oyster restoration since 1960 has been dredged shells from buried shell deposits. The sources of dredged oyster shell for Maryland’s repletion program are dwindling, and permits to dredge shell deposits from the upper bay may become more difficult to acquire. Estimates of available shell from the 1960s suggested that sources for dredged shell would last for about 50 years; after 40 years of planting these sources have been largely exploited. Wesson (VMRC, Newport News, personal communication, 2002) has estimated that 6 million to 8 million bushels of fossil shell could be produced annually in Virginia and, if properly managed, restoration efforts could continue for many years based on using dredged shell, processed shell, and alternative cultch materials. Permits have been issued to dredge shell deposits in Virginia. Resource managers are looking to alternative materials for cultch as well as material to construct reef cores. Alternative materials should be evaluated to determine properties that will be advantageous for reef construction. SOCIAL AND CULTURAL ASPECTS OF RESTORATION Restoration efforts have cultural-environmental meaning in addition to ecological and economic benefits. Some of this cultural-environmental
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Nonnative Oysters in the Chesapeake Bay meaning is linked to ecological benefits, since it contains the values and beliefs that individuals draw on to motivate themselves to be involved and supportive of oyster restoration. What is the relevance of symbolic and cultural meanings of oyster restoration to discussions of whether current restoration or repletion efforts are ecologically or economically successful? The average environmentally concerned citizen in Maryland and Virginia cannot be expected to understand the intricacies of oyster management and restoration under the current ecological and economic conditions. Most have an understanding that oysters filter water and that historically the bay was full of oysters and the waters were cleaner. Most will have the environmental belief that the biggest threat to the bay ecosystem is poor water quality and that current restoration efforts are attempting, without much progress to date, to restore oyster populations to levels that will result in improved ecological conditions. What is also important to consider when evaluating current restoration efforts, in addition to the ecological and economic impacts, are the cultural perceptions and attitudes surrounding oyster restoration as a cultural-environmental activity in and of itself. Restoration has strong public support and provides bay state citizens with hands-on opportunities to contribute something to help the bay through oyster gardening and monitoring programs. It is important to include in the evaluation of the current restoration programs an assessment of the cultural-environmental significance of the restoration efforts from a public perspective. This is particularly important given the environmental value and positive meaning applied to things native, pristine, and historic in the Chesapeake Bay. For example, the most widely disseminated and publicly influential annual status report on the bay’s health is the Chesapeake Bay Foundation’s State of the Bay Report, which uses an index to evaluate the current status of a range of bay resources and ecological parameters. The index scores 100 as the level of each resource/parameter before John Smith sailed up the bay. For the past 2 years oysters received a score of 2. For 2002 the average score for all resources/parameters was 27. That is a long way from pristine, but there is obvious environmental value in promoting the pristine as the ecological benchmark. To reemphasize: concepts of native, pristine, and historic carry strong cultural meaning to environmentally concerned and active bay state citizens, who will almost certainly, whether implicitly or explicitly, apply these cultural values to discussions of the current oyster restoration efforts. How they do so and the ecological and economic significance of these cultural factors are legitimate and important social science research questions (see the more extensive discussion of these issues in Chapter 5). There is precedence from other restoration efforts for a contested view
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Nonnative Oysters in the Chesapeake Bay of “restoration” leading to strong resistance or support by multiple stakeholders to what could be argued as the ecologically correct and feasible restoration activities (Gobster and Hull, 2000). Social science and humanistic research on restoration has found that it means many things to many people and that very few people are against restoration in general. However, what seems to trigger strong reactions of approval, disapproval, and support are the specific activities and practices undertaken during restoration (Gobster and Hull, 2000). The significance of this latter point for oyster restoration, and specific examples exist from other ecosystems as well, is the possibility that the activity of introducing a nonnative versus restoration of the native species in the Chesapeake Bay could be a practice that touches strong cultural-environmental values. A possible reduction of effort to restore the native oyster population (and perhaps its fishery), despite the acknowledged and recognized difficulties of this effort, could be met with resistance by people who value native species and pristine ecosystems and should be raised as a research and public policy concern. Restated, the bay is a “heritage seascape,” with strong cultural beliefs and values with regard to protecting and maintaining that environmental heritage. This heritage in turn is linked to the concepts of pristine, native, and historic. The risks of such perceptions and oppositions arising may be increased given the recent public concern and media coverage of the presence of northern snakehead (Channa sp.) in Maryland in 2003. SUMMARY The potential for restoring the Eastern oyster, C. virginica, to self-sustaining populations is a critical issue in restoring the overall integrity and functionality of the Chesapeake Bay ecosystem. However, it is also important to understand that restoring productive oyster reef habitat is only one part of a complex ecosystem, and resource managers and researchers must guard against the sentiment that oyster restoration can single-handedly resolve all of the ecological and environmental problems facing the bay. Successful restoration should result in a combination of positive effects that are inextricably linked and the synergy of these effects should be evaluated when determining the success of oyster restoration projects. Restoring oyster populations should: increase oyster populations that ultimately form self-sustaining reef communities that contribute to species diversity, trophic dynamics, and community stability;
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Nonnative Oysters in the Chesapeake Bay establish functional reef communities that perform specific ecological services contributing to the overall water quality, nutrient cycling, hydrodynamics, and habitat aspects of the estuarine system; and increase harvests that result in revenues that provide economic benefits to all sectors of the oyster industry. Although restoration efforts have made limited progress in establishing sustainable oyster populations, there remains some optimism that a more comprehensive management approach will ultimately achieve recovery of the oyster resource. A comprehensive management approach relies on applying a more stringent genetic improvement component to develop disease-resistant strains based on newly emerging technologies; selecting locations where environmental conditions are favorable for recruitment, growth, and survival; designing and constructing optimal reef habitat; avoiding disease, including growing oysters in areas or in a manner that reduces the chance of infection and not using infected seed; managing multiyear class distributions for sustainability; and providing a long-term time frame for success. Restoration efforts have cultural-environmental meaning in addition to ecological and economic benefits. Some of this cultural-environmental meaning is linked to values, beliefs, and perceptions that individuals draw on for protecting and maintaining their environmental heritage. This is particularly important given the environmental value and positive meaning applied to things native, pristine, and historic in the Chesapeake Bay.
Representative terms from entire chapter: