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

Prepared By : Nesma Mohammed