Abstract
Worldwide, shrimp farming has proven to be both
lucrative and environmentally damaging. This same pattern is prominent
in Texas, which leads U.S. aquaculture production. To continue to meet
market demand while protecting the coastal environment and the wild shrimp
capture fishery, shrimp culture must adopt techniques that are ecologically
sustainable. Application of the Precautionary Principle would lead shrimp
farmers and agency regulators to adopt a conservative approach until the
absence of an environmental threat has been demonstrated. Ecological sustainability
will be possible by: (1) reducing nutrient input and treating shrimp pond
effluent with simple, well-demonstrated techniques such as sedimentation
ponds, polyculture with filter-feeding species like clams and oysters,
and excess nutrient removal by passage through especially-designed wetlands;
(2) shifting emphasis to the culture of indigenous shrimp species which
do not pose a threat to coastal ecosystems; and (3) raising shrimp at lower,
but still profitable, densities to avoid epidemics of non-indigenous pathogens.
Introduction
The United States leads the world in consumption
of shrimp. While the U.S. wild shrimp capture fishery is a viable and valuable
resource (1996 harvest of 317 million lbs of whole shrimp worth $509 million),
it is greatly exceeded by the volume and value of shrimp imported from
other nations (582 million lbs of processed shrimp worth $2.4 billion in
1996 (U.S. Dept. Comm. 1996, 1997)). The volume of imports, most produced
by aquaculture, has depressed prices for wild-caught U.S. shrimp (TPWD
1995). Most (69%) of the wild shrimp harvested in the U.S. are produced
in the Gulf of Mexico (219 million lbs worth $401 million in 1996). Thirty-five
percent of the 1996 Gulf harvest (76 million lbs) was landed in Texas.
It would appear that Texas, with its long coastline, barrier island estuaries and subtropical climate, is ideally located for shrimp aquaculture that could partially offset the huge existing shrimp trade imbalance. Indeed, Texas is the leader in shrimp aquaculture among U.S. states, producing 70-80 percent of U.S. production. But the same barrier islands that create highly productive estuaries, by impeding the flow of nutrients to the sea, also restrict the interchange of seawater and the dilution of shrimp farm effluent. Turnover times for bay water volume range from days on the upper coast (Sabine Lake 7.3 days) to years along the middle coast (Copano-Aransas Bays 4.2 yr) and negative net freshwater inflow on the lower coast (hypersaline Laguna Madre; Armstrong 1987). In some instances shrimp pond effluent may enter these bays and slosh back and forth with tidal movement for days.
Shrimp aquaculture has established worldwide patterns (Chen, 1995; Lin, 1995; Qingyin et. al, 1995; Winarno, 1995; Stern, 1995). Some shrimp farmers have first raised indigenous shrimp, gradually increasing the density of shrimp in the farm ponds until metabolic wastes lower water quality, creating physiological stress, and disease epidemics erupt. Other farms, more heavily capitalized, have gone straight to the importation of non-indigenous species and intensive (high density) culture. When non-indigenous shrimp are imported, the same water quality conditions prevail, and non-indigenous diseases may erupt. As the density of the shrimp farms in a specific geographic area increases, regional water quality declines, the farms become unprofitable, and absentee farm owners relocate to initiate the process once again, leaving thousands of acres of useless ponds and land in their wake. In Taiwan, production of Penaeus monodon and P. penicillatus peaked in Taiwan in 1987, and Penaeus japonicus and Macrobrachium rosenbergii peaked in 1991 (see Fig. 1); all succumbed to diseases (Chen 1995). This pattern has been repeated in the U.S. where the principle culture species has been the non-indigenous Penaeus vannamei.
Research with shrimp culture began slowly in Texas in 1953-54, with greater effort in 1963 (Hightower & Treece 1992), primarily to learn identification features of planktonic shrimp. As techniques to successfully rear larval shrimp matured in the late 1960s, federal and state agencies shifted their efforts toward grow-out ponds. Non-indigenous species (Penaeus vannamei, P. stylirostris) were first imported in 1968. These required captive reproduction. Large scale commercial operations began in 1981. Both successes and failures have resulted, with frequent changes in ownership and names. Taiwanese investors purchased and expanded existing farms in 1989 and 1990, introducing Asian techniques and migrant workers to the industry in Texas. Several diseases, native and non-indigenous, have hampered operations.
The challenge is to ensure that this aquaculture is conducted in an environmentally responsible and ecologically sustainable manner. The search for a sustainable protocol is a decade old (Olsen & Arriaga 1989). Shrimp farming has been judged as one of the most resource-intensive food production systems in the world, and characterized as an ecologically unsustainable throughput system (Larsson et al. 1994). The amount of animal protein input as feed typically exceeds the amount of animal protein produced as shrimp. The input-output rule (Goodland & Daly 1996) applies: the harvest rate of renewable-resource inputs (shrimp larvae, entrained organisms) should be within the regenerative capacity of the natural system that generates them; discharges of wastewater should be within the assimilative capacity of the local environment to absorb them without unacceptable degradation of its future waste-absorptive capacity or other important services. To date, aquaculture facilities have raised the ire of recreational fishers; coastal communities; local grassroots, state and national environmental organizations; and the wild-shrimp fishers. This is not a struggle between shrimp fishers and shrimp farmers for market share; the wild-shrimp fishery can never meet existing and future market demand. It is a struggle between shrimp farmers and a broadly-based coalition that wishes to protect coastal streams and estuaries from real or perceived threats to the vital shellfish and finfish nurseries that the Texas coast provides.
The Concept of Sustainability
From the viewpoint of a shrimp farmer sustainability is a simple concept: they require an adequate supply of clean water, a handy receptacle for their wastewater, and some mechanism to control diseases. By raising an imported exotic shrimp species, artificially produced, they do not compete with the shrimp fishers or other shrimp consumers for the native wild shrimp populations.
From the environmentalist viewpoint sustainability is not that simple; neither is the sustainable development of a shrimp aquaculture industry. Sustainable development has been defined as “the management and conservation of the natural resource base and the orientation of technological and institutional change in such a manner as to ensure the attainment and continued satisfaction of human needs for present and future generations; such sustainable development conserves land, water, plant and animal resources, is environmentally non-degrading, technically appropriate, economically viable, and socially acceptable” (FAO, 1996). Goodland and Daly (1996) have defined sustainable development as “development without growth in throughput of matter and energy beyond regenerative or absorptive capacities” and recognize three categories—social, economic, and environmental sustainability.
Environmental sustainability is most readily apparent and requires maintenance of natural capital comprised of intact ecosystems and the structural and functional services which they provide. In this instance, the loss of estuarine organisms entrained in water withdrawn for shrimp ponds must not exceed the natural regenerative capacity of the estuary. As this water is recirculated back to the estuary, its nutrients, waste materials and oxygen demands must not exceed the assimilative capacity of the receiving ecosystem. Furthermore, the inevitable escape of the exotic shrimp must not disrupt the estuarine and nearshore ecosystem structure and functions. Finally, any exotic disease organisms which may have accompanied the introduction of exotic shrimp must not result in epidemics among the previously unexposed native shrimp populations or other susceptible organisms. Once a shrimp farm is hooked to its adjacent estuary by water withdrawal and discharge pipes, its full “ecological footprint” (Folke et al. 1998, Larsson et al. 1994) and the continued health of the receiving ecosystem must be taken into account.
Economic sustainability requires the maintenance of the four forms of capital—natural, social, human and human-made. Historically, aquaculture has been primarily concerned with only human-made capital, specifically the infrastructure comprising the farm. The economic factors important to aquaculturists include gross and net revenue, fixed and variable costs of production, profit and return on investment, the cost of regulatory compliance, and market demand and structure. This view must be expanded to include potential impact on other industries, such as the wild shrimp capture fishery, the recreational fishery, and tourism. If shrimp aquaculture threatens ecosystem health, the economic impacts can be substantial. Natural capital — the air and water which the farms circulate, the microscopic organisms with which they “seed” their grow-out ponds to feed the developing shrimp, the waste-treatment capacity of the receiving ecosystem — have simply been taken for granted. Environmental costs have been externalized and born by the surrounding communities. Impacts on human capital, and the livelihood of neighbors, have been considered unfortunate indirect by-products of progress.
Social sustainability requires the maintenance and replenishment of social and human capital. Social capital is the shared values of a community and its social groups. This requires that the shrimp farm become an accepted thread in the fabric of the surrounding community. Human capital involves the health, nutrition and education of the workforce and neighboring community.
The Economic Framework
An economic comparison of the capture and culture
shrimp fisheries for 1996 is presented in Table 1.
Table 1. 1996 Economic Comparison of Capture and Cultivated Shrimp Fisheries
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| SHRIMP BOAT
LICENSES
Texas Resident
TOTAL SHRIMP FARMS |
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| Combined
Brown, Pink, &
White Shrimp
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| Ex-vessel
/Farm
Value ($ million) |
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| Value per pound |
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Note: Some boats obtain more than
one type of license.
Shrimp aquaculture development in Texas has been supported and subsidized with public funds expended by several federal and state programs. Major support has been provided by the U.S. Department of Agriculture Marine Shrimp Farming Program and the U.S. Department of Commerce Sea Grant program. Lesser support has come, at various times, from the U.S. Bureau of Commercial Fisheries and its successor, the National Marine Fisheries Service, the U.S. Army Corps of Engineers, the U.S. Fish & Wildlife Service, Texas A&M University and its Texas Agricultural Extension Service, the University of Texas, and the Texas Department of Agriculture and Texas Parks and Wildlife Department. Support from industry and local government has been extended to specific projects. Most of this support has been focused on fostering aquaculture development. The need for the simultaneous protection of the wild shrimp fishery, although recognized, has received far less attention and funding. The success, failure and emphasis of these programs collectively have influenced the direction of aquaculture development.
The Regulatory Framework
In Texas, the regulation of shrimp farms has been fractured between many state and federal agencies. Aquaculture comes under the auspices of the Texas Department of Agriculture (TDA) but their activity is limited to registration of aquaculture facilities and the promotion of aquaculture in Texas. A permit from the U.S. Army Corps of Engineers is typically required for construction of a structure to withdraw fill and exchange water but Corps’ consideration of environmental impacts is perfunctory and nonfunctional. A permit from the Texas Parks and Wildlife Department (TPWD) is required to import an exotic shrimp species for culture. The discharge of exchange or drainage water is regulated by the Texas Natural Resource Conservation Commission (TNRCC). Theoretically, this discharge also is regulated by the U.S. Environmental Protection Agency (EPA) National Pollution Discharge Elimination System (NPDES) program. Shrimp feed components are regulated by the Texas Department of Health (TDH) and the federal Food and Drug Administration (FDA). The temporal development of this regulation is presented in Table 2.
1975 Legislature granted Texas Parks & Wildlife Dept. (TPWD) authority to prohibit non-native species of fish in Texas waters.
1979 Code of Federal Regulations defined "Concentrated Aquatic Animal Production Facilities" and required a National Pollutant Discharge Elimination System (NPDES) permit from them.
1986 Texas Dept. Commerce began promoting the burgeoning mariculture industry.
1987 Legislature exempted mariculture facilities (using brackish or salt water) from water rights permits. Hung Shrimp Farm began construction of facility in Arroyo City on Arroyo Colorado. Texas Water Commission (TWC) did not require a wastewater discharge permit.
1989 Legislature passed Fish Farming Act to promote aquaculture by establishing a regulatory infrastructure to coordinate a uniform approach to industry. Created Aquaculture Executive Committee (AEC). Transferred all regulatory authority, save exotic species, from TPWD to Texas Dept. of Agriculture (TDA). Neither AEC nor TDA Regulatory Div. Funded.
1991 Legislature amended Fish Farming Act. Aquaculture was explicitly designated an agricultural activity. AEC given new duties, including issuing license for aquaculture. TWC reversed itself, requiring wastewater discharge permit from Hung Shrimp Farm.
1993 AEC presented Aquaculture Strategic Plan to Legislature. New legislation structured responsibilities.
1994 TPWD, TNRCC, U.S. Fish & Wildlife Service and U.S. Environmental Protection Agency undertake a joint study of shrimp farm discharge; conclude that discharge does have local water quality impacts.
1995 Proposed legislation authorized Texas Natural Resource Conservation Commission (TNRCC) to regulate total suspended solids within wastewater discharge from mariculture facilities. TNRCC would be prohibited from enforcing effluent limits for 4 years to allow industry to compile data on discharge. Amendment placed 4 year moratorium in construction of new aquaculture facilities. Legislation failed to pass both Houses.
1996 Senate Natural Resources Interim Subcommittee submitted report to Legislature recommending abolishment of TDA regulatory authority of aquaculture industry, desingation of Texas Animal Health Commission as responsible for disease in aquaculture facilities, abolishment of the AEC, and establishment of interagency permit review.
1997 The Legislation did not pass
due to a premature adjournment.
Aquaculturalists consider the extent of human-impact
of aquaculture on society as their social framework. This includes such
factors as extent of local ownership; the number of production level jobs
provided and their wage levels and benefits; the use of local products
such as feed; local consumption of the product; and competition with existing
local industries. In addition to the shrimp farmers and their workforce,
there are several other stakeholder groups that must be considered: the
wild shrimp capture fishery workforce, the recreational fishery users and
workforce, homeowners and residents near the shrimp farms, the neighboring
communities and their local governments, and the environmental groups and
individuals focused on protecting the natural environment and their stakeholder
interests. In Texas, some farms have been purchased or established with
foreign capital and operated by migrant foreign workers. Other farms were
indigenous or corporate in nature. Thus far, shrimp aquaculture in the
USA has avoided the massive social disruptions experienced in Asia and,
to a lesser extent, Latin America (Hagler et al. 1997).
The Natural Framework
All three major commercial species of shrimp in Texas
(brown shrimp, Penaeus aztecus; white shrimp, P. setiferus; pink shrimp,
P. duorarum) spawn in Gulf waters but grow and develop in the coastal estuaries
for some months before migrating back to the Gulf as juveniles. During
this period they play key ecological roles in the food webs of the estuaries.
They recycle nutrients by feeding on organic matter and microorganisms
in sediments. They are important prey for many estuarine and marine fishes,
invertebrates and birds (McFarlane, 1993). The introduction of an
exotic shrimp species into this ecosystem, or the initiation of a disease
epidemic among the shrimp populations, could have unpredictable impacts
of significant consequence, perhaps affecting finfish fisheries.
The combined brown, pink and white shrimp harvests
(excluding bait shrimp) for 25 years are shown in Figure 2 (data from Robinson
et al. 1997). The average harvest was 78.6 million pounds worth $147.6
million at dockside. The Texas shrimp industry, including processors and
distributors, generates about $600 million per year and employs about 15,000
workers (TPWD 1997). Both bay and gulf fisheries are overcapitalized and
catch-per-unit effort has declined. Growth overfishing has occurred, resulting
in a general decrease in large shrimp and an increase in small shrimp landed
(TPWD 1995). The trend appears to be ecologically unsustainable; too many
fishers chasing too few shrimp.
Real and Perceived Threats to the Environment
The environmental impacts of shrimp aquaculture fall into three categories:
1. The impacts associated with the withdrawal, use and return of coastal
waters,
2. The impacts which may result from escape of a cultured, non-indigenous
shrimp species, and
3. The impacts which may result from the release of pathogens and parasites
from both indigenous or non-indigenous cultured shrimp.
Water Quality — The impacts of aquaculture on water quality are ubiquitous, global and well documented (deFur & Rader 1995, Landesman 1994, Flaherty & Karnjanakesorn 1995, Hopkins et al. 1995, Goldburg & Triplett 1997, Boyd 1995, 1997). Nutrients and waste are added to the shrimp ponds in the form of unconsumed feed, metabolic wastes and excreta. Other additives include fertilizer to stimulate phytoplankton blooms which support the early life stages of shrimp, and antibiotics to control diseases. Shrimp ponds are the aquatic equivalent of terrestrial feedlots regarding the concentration of husbanded animals, the input of nutrients, and the creation of waste, all hidden from view in the murky waters. Pond bottoms tend to become acidic and anaerobic. Since shrimp are bottom dwellers affected by these deteriorating conditions, aquaculturists ameliorate their micro-environment by exchanging pond water and aerating the ponds. When the pond water, containing suspended and dissolved minerals and oxygen-consuming organic material, is released into the estuarine environment it may overwhelm the assimilative capacity of the receiving water body. Analysis of shrimp pond effluent in Texas has revealed that water quality standards established by the Texas Natural Resource Conservation Commission (TNRCC) for total suspended solids, ammonia nitrogen, and carbonaceous biochemical oxygen demand have been exceeded on occasion (Samocha & Lawrence 1995).
Non-indigenous Species — The impact of introduced species, typically freed from their predators, parasites and pathogens, upon their receiving environment is a problem of global proportions (USC OTA 1993, DeVoe1992). The FAO Code of Conduct for Responsible Fisheries recommends that a “precautionary approach” be utilized regarding species introductions (FAO 1996). There is a high probability that the impacts of species introduction may be irreversible and unpredictable. Fisheries management should reduce the risk of adverse impacts of introductions on wild ecosystems and their associated capture fisheries. The International Council for the Exploration of the Sea (ICES) Code of Practice to reduce the risks of adverse effects arising from introductions and transfers of marine species recommends that a brood stock be established under quarantine conditions and only the first generation progeny, demonstrated to be free of diseases and parasites, be introduced into the natural environment. This recommendation is routinely ignored by academic and governmental institutions and agencies permitting the introduction of non-indigenous species. The Gulf of Mexico Fishery Management Council (1996) recommends that native species receive priority as candidate culture species. The Council opposes use of non-native species in mariculture systems unless it has been demonstrated that such use will have no detrimental impacts on native species. No studies of the potential impacts of escaped non-indigenous shrimp species on local ecosystems have ever been undertaken. Such escapes have occurred twice in Texas (TPWD 1997). In 1991 hundreds of pounds of P. vannamei were accidentally released from a shrimp farm and recovered from the Arroyo Colorado and Laguna Madre, up to 65 miles distant. In 1997 P. vannamei appeared in trawls in Matagorda Bay; four shrimp farms are in the vicinity but the source was not determined. The Texas Parks and Wildlife Department (TPWD), which is a member of the Council, and issues permits for the introduction of exotic shrimp species into Texas, routinely ignores the recommendations of the Council.
Non-indigenous Pathogens — The TPWD currently permits the introduction of Penaeus vannamei to coastal areas, and Penaeus stylirostris to areas more than 200 miles from the coast. All imported shrimp stock must be certified as disease-free. Shrimp farms raising Penaeus vannamei in Texas suffered major losses from the Taura Syndrome Virus (TSV) in 1995, 1996 and 1997 although all were certified as disease free. Nuclear breeding centers which produced the shrimp blame the TSV epidemics on farm biosecurity. The near-simultaneous eruptions of these epidemics on several farms raise the suspicion that environmental (pond physico-chemistry) or developmental (specific growth or molt stage) factors may be involved, whether or not the shrimp were infected when they reached Texas. All three commercial native shrimp species have been infected with TSV under laboratory conditions (Overstreet et al. 1997). Penaeus setiferus was killed by TSV, and both P. aztecus and P. duorarum can serve as carriers or reservoir hosts of TSV without necessarily exhibiting the disease. Significantly, brine shrimp (Artemia sp.) were allowed to feed on TSV-infected P. vannamei shrimp tissue. When the 48 hr old brine shrimp were subsequently fed to P. setiferus and P. vannamei, they all died. This demonstrates that TSV can be incorporated into a food chain and transmit the disease to other species.
Penaeus stylirostris is highly susceptible to the IHHN (infectious hypodermal and hematopoietic necrosis) virus. The TPWD recently resumed issue of import permits for P. stylirostris for culture greater than 200 miles from the coast, apparently assuming that this distance would be sufficient to protect coastal areas from contaminated wastewater. Since the Law of Gravity has not been repealed and water still runs downhill to the sea, environmentalists are concerned that IHHNV may be transmitted to freshwater river shrimp (Macrobrachium ohione) or brackish-water grass shrimp (Paleomonetes spp.) and eventually reach the estuaries. Shrimp viruses have been redistributed globally through the propagation of cultured shrimp species (Lightner & Redman 1992).
Traditionally, ecologists have ignored the role of
disease in ecosystem function and structure (Real 1996). A long-standing
paradigm has assumed that host and pathogen would adapt to each other to
the point where pathogens would have little impact on host survival and
reproduction, since it has been assumed to be in the pathogen’s best interest
not to eliminate its host. Academicians, aquaculturists and regulators
have all voiced opinions that the indigenous shrimp would adapt to the
presence of a new pathogen. This “prudent pathogen” hypothesis has recently
been challenged (Real 1996). In any event, the inattention of fishery and
regulatory biologists in Texas and elsewhere to the perceived threat of
introduced pathogens indicates that the concept, at least, is alive and
well, and has resulted in complacent attitudes.
The Path to Ecological Sustainability
Water Treatment — The prognosis for achieving ecological sustainability regarding water pollution is very good, if the TNRCC and USEPA will require and enforce stricter regulations. The techniques for improving pondwater discharge are well established and proven (Hopkins et al. 1995). Holding ponds to increase sedimentation before discharge, polyculture with filter-feeding molluscs such as mussels, clams and oysters to remove microscopic algae, and flow through various wetlands to strip excess nutrients have all been successfully demonstrated. Changes in the shrimp feed to lower animal protein content, and changes in feeding methodology to reduce wastage, can reduce excess nutrients in the ponds. Some efforts to introduce benthic bacteria to the pond environment to facilitate nutrient recycling have been initiated. Two attitudinal changes will be necessary. Shrimp farmers will have to view polyculture as a cost-effective waste treatment system that may produce some income, but will be worthwhile even if a marketable product does not result. The regulators (TNRCC and USEPA) will have to include biological pollutants, in this instance pathogens, parasites and non-indigenous shrimp species, in their suite of regulated pollutants. Both agencies have been reluctant to depart from their traditional physico-chemical parameters. In addition, it will be necessary to determine the assimilative capacity of those estuaries surrounded by multiple existing or proposed shrimp farms.
An unresolved issue is the application of antibiotics, typically added to feed, for the control of bacterial and similar diseases. The U.S. Food & Drug Administration has not approved the use of any antibiotic for cultured species to be used as human food. Since 1991, under the auspices of an INAD (investigational new animal drug) permit, oxytetracycline (OTC) routinely has been used at a number of Texas shrimp farms to control NHP (necrotizing hepatopancreatitus) disease (a.k.a. Texas pond mortality syndrome), a suspected bacterial or rickettsia infection (Brock & Main 1994; GCRLC 1996). The approach has concentrated on the efficacy of the antibiotic to control NHP and the withdrawal period necessary to clear OTC from shrimp tissue. The drug is applied via the feed. Since not all feed is consumed, and disintegration of feed pellets is rapid, the drug enters the pond environment. No studies have been conducted to assess the impact of the drug on the microbial community of the pond or the receiving environment. The use of antibiotics should be avoided as much as possible; if used, effluent retention ponds should be sized to accommodate oxidation and deactivation of the compounds before release to the receiving environment. Resistant pathogenic bacteria can evolve with the overuse or abuse of antibacterial agents (Folke & Kautsky 1989).
Non-Indigenous Species — Promoters of non-indigenous cultured shrimp point to the fact that there are no known instances where a non-indigenous shrimp species has become established in local waters. This is little cause for comfort; it should be remembered that, once established, non-indigenous species are virtually impossible to eradicate. The world biota is becoming homogenized due to the successful invasion of thousands of non-indigenous species, whether deliberately or accidentally introduced. There are approximately 4,000 exotic plants and 2,300 exotic animals in the U.S. alone (Stein & Flack, 1996). The biological impact of a successful shrimp introduction is unpredictable but potentially catastrophic due to the key role that shrimp play in coastal estuaries.
The role of the U.S. Marine Shrimp Farming Program (USMSFP) and the Sea Grant College Program needs reevaluation. Shrimp farmers initially had greater success in raising, and preferred the larger size of, the Pacific white shrimp, Penaeus vannamei, compared with native shrimp species. The USMSFP Oceanic Institute has been successful in the technically-difficult “domestication” of P. vannamei and exported their product to the U.S., where it is non-indigenous, and Central and South America, where it is native to Pacific waters but not the Caribbean Sea or Gulf of Mexico. This “genetically improved” product has proven particularly susceptible to the Taura Syndrome Virus, its natural pathogen, under culture conditions. Most subsequent research has focused on P. vannamei to the near-exclusion of native species. P. vannamei has escaped into Texas waters at least twice and into South Carolina waters. The Taura Syndrome Virus has followed the species into both states. The promotion of P. vannamei as the preferred species has become part of the problem, rather than its solution.
The climate of Texas permits only a single crop of
farmed shrimp each year. Native species manage two crops by temporal spacing.
Brown shrimp enter the estuaries as postlarvae in spring and depart as
juveniles during the summer; white shrimp enter in early summer and depart
in the fall. If culture efforts were refocused on these native species,
it might be possible to raise two crops per year, just as nature does.
Non-indigenous Pathogens — The response of the USMSFP
to shrimp farm disease problems has been the promotion of specific-pathogen-free
broodstock and high-health seed for shrimp producers. This represents a
high-technology solution to a low-technology problem. Theoretically, only
certified disease-free shrimp stock can be imported into Texas, yet widespread
epidemics of the TSV occurred in 1995, 1996 and 1997. Diseases are
best controlled by reducing the density of the shrimp stocking. It is uncertain
whether a grow-out pond, once infected with a virus, can ever be completely
disinfected. A change in policy to producing only native shrimp stock for
shrimp farms would remove the threat on non-indigenous pathogens, but do
little to control indigenous pathogens. There is one recorded instance
of a non-indigenous pathogen being introduced into wild shrimp populations
(Lightner et al. 1992). The infectious hypodermal and hematopoitic necrosis
virus (IHHNV) was absent from the Gulf of California until imported shrimp
were cultured in the area. A native shrimp, Penaeus stylirostris, subsequently
suffered a drastic population decline which persisted for several years.
Two different non-indigenous viruses apparently have been recovered from
native shrimp in Texas — the white spot syndrome virus and the yellow head
virus (GCRL Consortium 1996). Since a diseased shrimp is likely to be quickly
eaten, and a dead shrimp immediately scavenged, in Texas estuaries, it
would be very difficult to detect the presence of a disease epidemic in
a wild population. To overcome this difficulty, the TPWD has recently launched
a program to detect pathogens in shrimp collected during routine monitoring
of finfish and shellfish populations, apparently the first effort of this
nature in the nation.
In some nations which export shrimp to the U.S., it is standard practice to harvest and ship shrimp at the first sign of disease, rather than lose or destroy them. Skilled practitioners can recognize these undersized diseased shrimp in U.S. markets (JSA 1997). Frozen imported shrimp thus represent a potential path for the introduction of non-indigenous pathogens into U.S. waters. Proponents of imported cultured shrimp argue that the pathogens are already introduced and their is no longer a need for concern. The efficacy of this path has not been demonstrated.
The Relative Risk of Being Wrong — In comparing the
relative worth of the capture shrimp industry versus the culture shrimp
industry, the relative risks of being wrong are completely out of balance.
Table 3 compares these fisheries for the period 1990 to 1996.
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The probability that the introduction of any non-indigenous species into a natural environment will succeed is very small. It is repetition of the event that ensures success. For example, the chance of winning the Texas Lotto lottery, selecting 6 numbers out of 50 correctly, is vanishingly small; 15,890,700 to 1. But since its inception in 1992, more than 300 people have succeeded. With hundreds of shrimp ponds and repetition every year, the successful introduction of a non-indigenous shrimp or pathogen becomes more inevitable. State and federal regulators, and the shrimp aquaculture community, should not gamble with the ecological sustainability of the state-owned and publicly harvested natural resources. The Precautionary Principle, taking a conservative approach to management issues until there is compelling evidence that the less conservative approach now routinely practiced actually poses no added risk (Botsford et al. 1997).
Armstrong, N.E. 1987. The ecology of open-bay bottoms of Texas: a community profile. U.S. Fish & Wildlife Service Biological Report 85(7.12), Washington. 104pp.
Baker, P. 1997. Case Study One: Coastal Shrimp Farming in Texas. p.117-130 in Murky Waters: Environmental Effects of Aquaculture in the US (R. Goldburg & T. Triplett). Environmental Defense Fund. Http://www.edf.org/pubs/reports/aquaculture/f_download.html.
Botsford, L.W., J.C. Castilla & C.H. Peterson, 1997. The management of fisheries and marine ecosystems. Science 277:509-515.
Boyd, C.E. 1995. Chemistry and efficacy of amendments used to treat water and soil quality imbalances in shrimp ponds. P.183-199 in Swimming Through Troubled Water (C.L. Browdy & J.S. Hopkins, eds.). World Aquaculture Society.
Boyd, C.E. 1997. Shrimp farming and the environment: a white paper. The Shrimp Council, National Fisheries Institute. Http://www.nfi.org/whitepapershrimpfarming.html.
Brock, J.A., & K.L. Main. 1994. A Guide to the Common Problems and
Diseases of Cultured Penaeus vannamei. World Aquaculture Society and the
Oceanic Institute, 242pp.
Chen, S., 1995. Current status of shrimp aquaculture in Taiwan. p.29-34
in Swimming Through Troubled Water (C.L. Browdy & J.S. Hopkins, eds.),
World Aquaculture Society.
DeFur, P.L., & D.N. Rader. 1995. Aquaculture in estuaries: feast or famine? Estuaries 18(1A);2-9.
DeVoe, M.R. (Ed.), 1992. Introductions & Transfers of Marine Species: Achieving a balance between economic development and resource protection. S.C. Sea Grant Consortium.
Flaherty, M., & C. Karnjanakesorn. 1995. Marine shrimp aquaculture and natural resource degradation in Thailand. Environ. Management 19(1):27-37.
Folke, C., & N. Kautsky, 1989. The role of ecosystems for a sustainable development of aquaculture. Ambio 18(4):234-243.
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