Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 92
4 Environmental Issues Aquaculture, like traditional agriculture, creates environmental impacts. These impacts have received extensive scrutiny because marine aquaculture in the United States is relatively new and often conducted in public waters that are used and observed by many. Currently, four federal and numerous state and local agencies are involved in the regulation or monitoring of various aspects of aquaculture operations, including environmental impacts. The issues associated with environmental aspects of marine culture opera- tions can be grouped into two broad categories: 1. impacts on the natural environment by the production systems, and 2. environmental requirements of the production systems, including im- pacts from and on other industries and interests (e.g., commercial fishing, recreation, human health). ENVIRONMENTAL IMPACTS OF MARINE AQUACULTURE Introduction Concerns about the environmental impacts of marine aquaculture include such diverse issues as waste from cages or ponds, introduction of non- indigenous species or disease, the presence of infrastructure associated with culture operations in public waters, and genetic alterations of wild stocks through escapement of cultivated animals or intentional releases for stock enhancement. 92
OCR for page 93
ENVIRONMENTAL ISSUES Aquatic Plants 93 Of all the types of aquaculture operations, aquatic plant cultivation poses the least threat to the marine environment. Aquatic plant culture may be beneficial because it tends to counteract the potential detrimental effects of a variety of other coastal activities including terrestrial agriculture, sewage treatment, residential development, and fish or crustacean aquaculture. Aquatic plant culture using traditional rafting techniques relies on available dis- solved nutrients and sunlight. Cultivated aquatic plants remove nutrients and limit eutrophication of the coastal environment. Aquatic plant culture employing rafting is insignificant in the United States, however, and rafting techniques may meet with resistance by boating interests or those concerned with the aesthetic aspects of a particular body of water. Shellfish The impacts of bivalve mollusk culture are also relatively innocuous, except in areas of highly intensive cultivation (e.g., mussel culture along the coast of Spain) (Figueras, 1989: Weston, 19911. Potentially adverse en- vironmental impacts are similar to those for other species: (1) physical displacement or interference with other activities, (2) disturbances to natu- ral phytoplankton communities (unlikely), (3) deleterious modifications of water quality through accumulation of wastes, (4) genetic contamination of wild stocks, and (5) introduction of species that compete with or are patho- genic to wild stocks (Weston, 1991~. The majority of shellfish culture in the United States takes place in the public domain, particularly in estuarine and nearshore marine waters (Burrell, 1985; Lutz, 1985; Manzi, 1985~. A small portion of this industry utilizes shore-based facilities. Shore-based facilities typically house the hatchery and nursery compo- nents of businesses whose grow-out operations are in the estuary or near- shore coastal waters. The shore-based facilities rely to varying degrees on coastal water, which is pumped ashore. Effluents from shore-based facili- ties may be either enriched with cultivated microalgae produced for hatchery use, or partially depleted of naturally occurring phytoplankton and particulate matter that has been consumed in a nursery system. In either case, the effluent will have slightly elevated levels of metabolites, principally ammonia. At present, virtually all shellfish production comes from open estuarine and nearshore waters, the use of which is generally regulated by the state. The degree of control exercised in shellfish cultivation varies dramatically. In many areas, shellfish cultivation is largely a matter of managing natu- rally recruited wild stocks. At the other end of the spectrum, more inten- sive operations deploy hatchery-reared spat into various types of floating
OCR for page 94
94 MARINE AQUACULTURE or submerged hardware that provides predator protection and facilitates management and harvesting. Such grow-out facilities may interfere with recreational or commercial activities (Burrell, 1985; Lutz, 1985; Manzi, 1985~. Benthic communities may be impacted by submerged structures or nets, shell debris, or fecal sediment, food, and deposition from floating structures (Figueras, 1989; Weston, 1991~. Their impacts on water quality and plankton communities are generally minor but may be measurable. Plankton is removed from the water and excrete (dissolved metabolites, feces, and pseudofeces) are then added to the water. Little, if any, change occurs in biochemical oxygen demand (BOD) and only a minor change in absolute dissolved oxygen concentration. The source of the shellfish stock may be of concern if it is genetically different, represents a nonindigenous species, or is imported from areas that may harbor nonindigenous pathogens. The potential for an adverse effect from such stocks is increased by the fact that the cultivated crop is gener- ally deployed directly into open waters, as opposed to pond or cage culture where there is some degree of confinement. Shrimp Virtually all shrimp farming in the United States employs ponds (Cham- berlain, 1991; Hopkins, 1991; Pruder, 1991), although several ventures have cultured shrimp in environmentally controlled greenhouse-covered tanks (Salser et al., 1978~. Some ponds are actually previously impounded wet- lands (Whetstone et al., 1988), and few attempts have been made at cultur- ing shrimp in net enclosures. Typically though, the ponds are constructed on high ground adjacent to a supply of seawater. Estuarine water is as satisfactory as ocean water. Saline groundwater may be satisfactory if the ionic composition is similar to that of seawater. A second component of the shrimp farming industry is hatchery production of postlarvae for stocking ponds. Hatcheries use relatively little water, but it must be of near-oceanic quality. There are several areas of concern relative to environmental impacts of shrimp farming. These concerns can be broadly categorized as (1) genetic- related threats to indigenous species; (2) disease-related threats to indig- enous species; and (3) threats related to water quality degradation in the effluent receiving stream. The probability of these impacts varies among the three geographic areas in which U.S. shrimp farms are concentrated: Texas, South Carolina, and Hawaii. U.S. shrimp culturists rely almost exclusively on a nonindigenous spe- cies Penaeus vannamei (Rosenberry, 1990; Wyban and Sweeney, 1991~. Postlarval seedling shrimp for stocking ponds are obtained from commer-
OCR for page 95
ENVIRONMENTAL ISSUES cial hatcheries in the United States and Latin America. concern that this nonindigenous species could become established and dis- place indigenous species, particularly the Atlantic and Gulf of Mexico white shrimp (P. setiferus). The possibility of hybridization among these species has been raised, but it does not appear to be a realistic concern. In response to concerns about the importation of nonindigenous species, research has focused on the development of native species that may have marine aquacul- ture potential (Sandifer et al., in press). However, the process of domesti- cation of shrimp stocks through selective breeding of indigenous species could impact the genetic diversity of wild stocks were there to be large- scale or continuous escapement of the domesticated animals. Thus, it is conceivable, although unlikely, that a highly selected line of an indigenous species could have as great or greater impact than imported nonnative spe- cies. This is the same concern expressed for hatchery stocks of salmonids. Although shrimp diseases are poorly understood at present, some dis- eases appear to be associated with particular geographic areas, species, or aquaculture operations. The pathogen of most concern is the infectious hypodermal and hematopoietic necrosis (IHHN) virus, which has been shown to cause stunting, deformities, reduced growth rates, or mortality in several species (Browdy et al., 1990; Kalagayan et al., 1990~. The response to IHHN infection is highly species-specific. Although no cases of aquaculture opera- tions causing disease outbreaks in adjacent wild stocks have been documented, continued vigilance, escapement prevention, and shrimp disease research are essential if this industry is to continue to develop in the United States. For shrimp culture in the United States to be competitive in the world- wide shrimp marketplace, farms must use intensive production technology (Sandifer, 1988; Wyban and Sweeney, 19914. The concentration of pollut- ants in the effluent increases with intensification due to higher feeding rates. The potential environmental effect of shrimp farm effluent is in- creased eutrophication of the receiving stream through nutrient addition if proper dilution rates are not mandated (Brune, 1990~. Water quality parameters of concern include BOD, ammonia, and suspended solids. Modeling of shrimp pond effluents based on the level of intensification and water exchange is now possible (Brune, 1990; Brune and Drapcho, 19911. Coupled with existing models of effluent dilution and ultimate oxy- gen decline in complex tidal receiving streams, this gives the farmer or regulator a powerful tool with which to predict environmental impacts. Delineation of an acceptable impact from an unacceptable adverse impact is still not clear, however. Research is currently under way to reduce the BOD and nutrient loads of effluents from intensive shrimp farms, and this is an obvious area in which technological advances could improve the possibilities for growth of shrimp farming in the United States (Sandifer et al., 1991a, b). 95 There is some
OCR for page 96
96 Finfish MARINE AQUACULTURE Although the culture of mollusks, fish, and crustaceans accounts for most of the production by the U.S. marine aquaculture industry, environ- mental concerns in some parts of the country are focused on floating cages used for salmon culture. To date, few long-term studies have been con- ducted on this subject in the United States and Canada; however, much research and environmental monitoring of net pens has been done over the past 20 years in Europe and Japan. Many of the early aquaculture projects were located in semienclosed areas with poor water exchange; consequently, the first studies on environmental effects showed significant but localized impacts (Rosenthal, 1985~. Recent comprehensive studies suggest that the environmental impacts of properly sited cages can be alleviated through the development of improved management and production systems (Gillespie, 1986; Weston and Cowan, 1988; Paramatrix, 1990; Cross, 1990~. However, the use of coastal habitat by aquaculture facilities may impinge on native species' habitat and cause reductions in the populations of the native organisms. Impacts From Waste Wastes from culture operations can have a variety of environmental im- pacts. Two primary concerns relate to water quality and benthic ecology. Water Quality Finfish or shrimp in ponds or tanks dramatically affect water quality primarily through excretions from feed inputs. Water quality differences between inlet and effluent waters are a function of the loading of fish, the water exchange rate (retention time), and the feeding rate. When water re- tention time is long, feed inputs are digested, either by the fish/shrimp crop or by microbial digestion, and mineralized. Major end products in the digestion process are dissolved nitrogen and phosphorus species (mainly ammonia and orthophosphate) and particulate matter. Only 20 to 30 percent of the nitrogen input as feed is assimilated into fish tissue (Krom et al., 1985; Porter et al., 19871. Ammonia is the primary end product excreted by fish, crustaceans, and mollusks (Campbell, 1973), and its release generally is proportional to the feeding rate (Colt and Armstrong, 1981~. These digested end products may be reassimilated by phytoplankton, protozoans, bacteria, and fungi. Such organisms have short life spans, and on their decay, nutrients are again mineralized into dissolved or particulate debris forms. This cycle continues until the material is finally (1) flushed
OCR for page 97
ENVIRONMENTAL ISSUES 97 from the system with water exchange, (2) deposited in more stable sedi- ments, (3) volatilized to the atmosphere, or perhaps (4) assimilated by or- ganisms large enough to be consumed by the fish/shrimp crop. When mate- rial that was once feed input exits the pond with water exchange, it is an effluent "pollutant." Water exchange is typically the greatest source of nitrogen loss from the system (Daniels and Boyd, 1989). Sedimentation of solids and sludge formation may be an important sink for nitrogen and other pollutants. 5iucige accumulations ranging from 11 to 38 percent of the feed applied have been reported, the differences being attributed to sludge digestion because of variable holding times (McLaughlin, 1981). It has been suggested that sludge accumulations decrease available habitat for shrimp, reduce the density of benthic food organisms, and cause direct toxicity due to hydrogen sulfide and other anaerobic metabolites (Cham- berlain, 1986). However, these impacts have not been documented, and healthy shrimp can be found in sludge deposits. In addition, populations\o\f benthic organisms are grazed nearly to extinction in intensive shrimp cul- ture ponds (Hopkins et al., 1988a,b), and very little hydrogen sulfide has been found free in the water column (Ellis, 19901. The more important impact of sludge accumulation may be the sludge digestion processes that demand oxygen and release bound nitrogen back into the system. If sludge Is a~scnargea warn one exchange water, it degrades the quality of effluent by elevating concentrations of BOD and solids. The fish/shrimp crop is a major source of oxygen depletion in densely stocked tank systems, and reoxygenation is provided via aeration equip- ment. At the stocking densities typical of pond culture, the primary oxygen consumers are the decay and photosynthetic organisms in the water column and pond bottom. The higher the pond feed input, the higher must the supplemental aeration rate be to maintain adequate dissolved oxygen at night (Hopkins et al., in press). The effluent dissolved oxygen is generally as high as that of the receiving body in aerated tanks and ponds. Pond effluent dissolved oxygen may be higher than that of the receiving body during the day due to photosynthetic activity. Cage systems are not artificially aerated and nave rapid water exchange. The water passing through the pen typically has a slightly lower dissolved oxygen and slightly elevated ammonia concentration. The mass balance of feed input and pollutant output is equal, less the small amount assimilated into fish tissue. However, the dilution rate is extremely high in pen culture, and much of the secondary food decomposition occurs outside the pen, as in a rapidly flushed tank system. Model predictions and field measurements downstream from salmon cage farms in Puget Sound typically show a de- crease of less than 0.3 milligram (mg) per liter in oxygen (Weston, 1986~. Salmon require high oxygen levels; therefore the impact of lowered oxygen levels is self-limiting. . . .. . . · .. ~
OCR for page 98
98 MARINE AQUACULTURE The principal nutrient contributed to the environment from cages is ni- trogen. Salmon annually produce between 0.22 and 0.28 gram (g) of dis- solved nitrogen (mostly ammonia) per kilogram of fish (Gowen and Bradbury, 1987~. This nitrogen results in an increase of approximately 0.02 mg/liter of ammonia downstream from the average salmon farm (Weston, 1986), a small fraction of the Environmental Protection Agency (EPA) water quality standards for ammonia. Salmonids are extremely sensitive to ammonia, so this impact, like oxygen reduction, may be self-limiting with salmon. Re- cent comprehensive studies by Paramatrix (1990) in the United States and Gillespie (1986) in Canada on salmon net-pen farms conclude that water quality impacts are slight, localized, and reversible. Similar opinions were expressed in presentations to the committee (Gowen and Rosenthal, 19901. The composition of waste from cultured fish differs little from that con- tributed naturally by wild fish, but it differs significantly from that of warm-blooded animals. The effect of culture operations on coliform, and particularly fecal coliform bacteria, is a water quality concern. A better understanding is necessary, including a clearer differentiation between fecal and total coliform (ICES, 1988a). Plankton Shellfish tend to remove phytoplankton from the water during filter feeding, which may decrease the food supply for other animals. Counterbalancing this is the fact that marine plankton growth is often nitrogen limited. As a result, fish farms have the potential to cause or exacerbate plankton blooms by virtue of the nitrogen produced. The recent increase in awareness of toxic plankton blooms worldwide has raised concerns that aquaculture might contribute to the problem (Whiteley and Johnstone, 1990~. Correlations between aquaculture and harmful blooms have been documented in Japan where intensive culture of finfish and shellfish occurs in poorly flushed bays (Nose, 19851. Other than in Japan, few, if any, cases have been docu- mented in which aquaculture has caused algal blooms (Gowen and McLusky, 19901. Marine aquaculture can be the victim of plankton blooms (Saunders, 1988; Shumway, 19901. Toxic blooms sometimes cause closing of shellfish beds and, in some cases, can be lethal to fish. Benthos Accumulation of wastes can alter benthic ecology and modify the chem- istry of growing waters. Net-pen marine aquaculture operations typically result in large amounts of solid wastes, including feces and uneaten food from fish pens, and pseudofeces and shell debris from mollusk culture. A
OCR for page 99
ENVIRONMENTAL ISSUES 99 portion of the solid waste produced in tanks and ponds is digested in situ when water retention times are long. Thus, the effects of their effluents on benthos may be less than those from pen culture systems. Settleable waste from culture operations may alter the ecosystem by changing the physical and chemical environment or by changing or reducing the numbers and species resident beneath net pens or downstream from effluents. Solid waste is estimated at between 0.5 and 0.7 g for each kilogram of fish produced (Paramatrix, 19901. Although the quantity of waste is significant, it tends to accumulate beneath the pens only in sites of less than 15 meter (m) depth and low current velocities (Weston, 1986~. Studies on existing net pen operations in North America show that even on large farms where accumulations do occur, the impact is confined to an area roughly 30 m around the pens (Weston, 1986; Cross, 1990; Paramatrix, 19901. Models based on current velocity, depth, loading rate, and other factors are now available to select sites where impacts of new farms will be mini- mal (Weston and Gowen, 19881. The same observation holds true for pond and tank systems. If current velocities at the effluent discharge site are high, dispersal and dilution minimize any effects on benthos. In addition, evidence indicates that benthic impacts are rapidly reversed when net pens are removed (Dixon, 1986~. Mollusk culture also can result in accumulation of waste (ICES, 1988a). Shell rubble directly below intensive mussel and oyster culture systems can result in significant effects on the benthos directly beneath such operations if the rubble is not collected, the culture site is not selected to minimize the impacts, or the site is not mobile. Accumulation of anoxic sediments has occurred in some shallow bays in Japan as a result of mussel and oyster culture (Nose, 19851. Accumulation of anoxic sediments has also been noted in pond culture of oysters where phytoplankton densities are high and large amounts of pseudofeces are be- ing produced. Although shell rubble does alter the benthos, it does not increase BOD, tends to stabilize sediments, and may provide settlement or attachment sites for wild shellfish. Regulation of Discharges Aquaculture facilities can produce sizable quantities of waste and dis- charge large volumes of effluents to surface waters. Therefore, aquaculture operations (along with agricultural operations) are faced with growing en- vironmental regulatory scrutiny. Although much of the regulatory activity has come from state and local sources, a number of federal statutes and regulations directly impact the management of aquaculture wastes and effluents.
OCR for page 100
100 The Clean Water Act MARINE AQUACULTURE The Clean Water Act (CWA) of 1977 (40 CFR) focuses on the protec- tion, restoration, and maintenance of the chemical, physical, and biological integrity of the nation's waters. The CWA authorizes the issuance of fed- eral National Pollution Discharge Elimination Systems (NPDES) permits for point source discharges (including delegation of the federal permit pro- gram to the states), and the development of areawide waste treatment man- agement plans, including best management practices (BMPs) for nonpoint sources of water pollution. Under the general NPDES permit regulations (40 CFR Part 122), "concentrated aquatic animal production facilities" are considered point sources requiring NPDES permits for discharges into wa- ters of the United States. "Concentrated aquatic animal production facili- ties" are defined as a hatchery, fish farm, or other facility that meets the criteria in appendix C of the Clean Water Act, or any such facility that the director determines is a significant contributor of pollution to waters. The criteria provided in appendix C generally include commercial-size marine aquaculture fish farms or other facilities that "contain, grow, or hold cold water aquatic animals in ponds, raceways, or other similar structures which discharge at least 30 days per year." Therefore, aquaculture production facilities that meet these criteria or are found to be significant contributors to water pollution are subject to NPDES permits under the Clean Water Act. Moreover, states may place additional requirements on these discharges. Because many states have been delegated the authority to issue federal NPDES discharge permits, some states issue joint federal NPDES/state permits. Some aquaculturists have suggested that aquaculture effluents should be treated as nonpoint sources of pollution (a different category under the CWA, analogous to runoff from agricultural fields as contrasted with dis- charges from a feedlot), which are presently less stringently regulated under the CWA. However, states and federal agencies are currently in the process of imposing stricter regulations on all nonpoint sources of pollution. For example, a study convened by the EPA administrator recently recommended that "the states and the federal government augment voluntary programs with increased use of regulatory authority for reduction of nutrient loadings of the Chesapeake Bay [from agricultural runoff]" (Chesapeake Bay Pro- gram, 19911. Managing Wastes and Effluents Aquaculture wastes and effluents can be managed through well-designed and operated recycling programs that beneficially utilize the "waste" prod- ucts as resources. Such programs include utilizing the organic solids to im-
OCR for page 101
ENVIRONMENTAL ISSUES 101 prove or fertilize soil, as animal feed supplements, or using the wastewater as irrigation water, cooling water, or for recycling to the same or other aquaculture production systems (Mudrak, 19811. Well-managed beneficial use practices can help conserve water supplies and significantly reduce the volume requiring disposal (Rosenthal, 1985~. Impacts From Introduction of Nonindigenous Species Agricultural production in the United States, as in most other countries, relies almost entirely on the cultivation of introduced species. Today, most animal and plant foods come from a relatively few species that are grown where suitable environments exist. Aquaculture also relies on introduced species that have excellent market value and acceptance and that are ame- nable to cultivation. Introductions of nonindigenous species raise the possibility that the in- troduced species will (1) compete with native organisms for existing eco- logical niches, (2) alter the food web, (3) modify the environment, (4) introduce new diseases, and/or (5) dilute native gene pools through inter- breeding, hybridization, or especially, ecological interaction. The biggest problem associated with nonnative introductions is lack of information about the short- and long-term impacts of the introduced species on its new envi- ronment. Unanswered questions about the long-term effects of introduced species include the following (Seter, 19901: · Competition via interference or exploitation: Will the introduced spe- cies occupy a previously untapped niche or compete with native organisms for existing niches? · Predation: What impact will the introduced organism have on the surrounding ecosystem? Will food webs be permanently altered? · Environmental modifications: Will water quality be affected? Will the introduced species physically alter its surroundings? · Hybridization: Will inhibition of reproduction or, at the other end of the spectrum, interbreeding dilute or degrade native gene pools, reducing the potential for future benefits from wild gene stocks? The transfer of aquatic species can occur through unintentional as well as intentional acts. Means of transfer are varied (Chew, 1990) and include the following: · transfer by water traffic on or in ships, especially ballast water (e.g., the recent introduction of the zebra mussel to the Great Lakes (Griffiths et al. 19911~; · escape or release of organisms transferred for other purposes, such as confined culture, direct consumption for food, or use as ornamentals (live
OCR for page 102
102 MARINE AQUACULTURE crabs, lobsters, and mollusks, are routinely transported worldwide, as are fish and invertebrates for the aquarium industry); · accidental transfer of a secondary species associated with the transfer of a target species (i.e., organisms transferred in or on their hosts); and · deliberate transfers and introductions for culture or fisheries enhance- ment. Examples of nonaquaculture sources of introductions include the trans- port of nonindigenous species on ship hulls and in ballast water, which led to the introduction of the Australian barnacle and Chinese mitten crab in Europe (Rosenthal, 1980~; the introduction of Pacific species into the At- lantic and vice versa through the Suez Canal (Vermeij, 19911; the inadvert- ent or purposeful release of a great variety of aquarium fish and plants, and the shipment and frequent release of live bait organisms (Courtenay, unpub- lished manuscript). Genetic Impacts Genetic changes of wild stocks can result from (1) straying of anadro- mous fish released for fisheries enhancement or ocean ranching, (2) escape from confinement facilities, or (3) purposeful release of cultured fish (Sattaur, 1989~. Some investigators suggest that the potential loss of ge- netic diversity in a species can negatively affect its present condition and, more important, potentially affect the species' ability to adapt to a changing environment (Hinder et al.~. Other workers in the field, however, consider the genetic effects of large-scale releases with a more benign and even positive attitude. For example, Mathisen and Gudjonsson (1978) argue against a purist opposition to mixing gene pools of Atlantic salmon for release. Genetic issues apply to all cultured species, but a recent controversy involves private salmon ocean ranching and public fisheries enhancement along the West Coast, where hundreds of millions of hatchery fish are released yearly (Waples et al., 1990~. Some hatchery fish, both private and public, will stray as will some fish from natural runs. The rate of straying of hatchery fish is influenced by release strategy and possibly by hatchery strategy; however, the influence of stray rate on the actual genetic impact has not been adequately evaluated. Interpretation is confounded because the frequency of the gene flow associated with natural straying is unknown. At present, the greatest environmental concern appears to be the poten- tial for overwhelming the wild gene pool with the more restricted gene pool of a hatchery stock through repeated and massive stock releases, as with salmon in the Northwest (Hetrick, 1991; Hindar et al., 19911. Clearly, the gene pool of any stock that is reared in a hatchery and originates from the
OCR for page 105
ENVIRONMENTAL ISSUES 105 cures are quite limited; federal certification procedures/laboratories are nonexistent; and qualified state certification operations exist in, at most, a few states. Fish and shellfish from U.S. capture fisheries must meet only public health criteria, even if they are being harvested for holding or shipment live to other areas (e.g., oysters, clams, scallops, mussels, lobsters, crabs). Rou- tine shipments of live shellfish and crustaceans intended for direct sale to consumers or for use as bait are seldom, if ever, examined for diseases, parasites, or accompanying organisms. Nevertheless, such shipments may be significant potential sources of disease (IOM, 1991~. Nor are frozen and fresh seafood products imported into the United States generally inspected for disease, although they may serve as an avenue of disease transfer to native stocks. Regulation of Fish Movement The federal government regulates movement of nonindigenous species through the Lacey Act (P.L. 97-79, as amended in 1981), and the states exercise varying degrees of control over the use and introductions of exotic nonindigenous species. Requirements include importation permits, an envi- ronmental risk report, inspection certifying the lack of disease, and in some cases, a disease history of the stock. In the majority of states, introduction of nonnative species requires au- thorization from a state conservation agency (King and Schrock, 19851. In many cases, standards for private hatcheries and farms exceed those applied to public hatcheries (Hicks, 19891. Importation of salmonid eggs and fish is highly regulated by federal and state agencies. Importation of fish is pro- hibited under most circumstances, and egg importations are restricted to inspected stocks from specific regions. Salmon egg and smolt importations are highly regulated, and in some states a quarantine period is required prior to introduction. The International Council for Exploration of the Sea (ICES), of which the United States is a member nation, has compiled a detailed and compre- hensive protocol for introduction of exotics (ICES, 1984), which has been suggested as a guide for all planned introductions of marine species (Sinder- mann, 19881. In the context of disease control, this protocol requires care- ful screening for disease organisms and holding brood stock in quarantine until the production of first-generation organisms. This protocol was used successfully in an introduction of eastern bay scallops from the United States to Canada. However, a problem limiting practical implementation of the disease protocol is that insufficient knowledge is available about the diseases or parasites of importance or about the diagnostic tools for most species (Sindermann, 19881. Lightner (1990), referring to the ICES
OCR for page 106
106 MARINE AQUACULTURE protocol and the FAO (1977) guidelines, stated that "for these guidelines to work, adequate quarantine facilities and qualified diagnosticians must be available." The problem is illustrated by the example of a penaeid shrimp disease in Hawaii. A strict quarantine system was established for the introduction of nonnative shrimp species based on the ICES protocol. The protocol was targeted especially to prevent introduction of the IHHN and other viral pathogens. Nevertheless, despite strict controls and apparently excellent compliance by the aquaculture industry, the IHHN virus was diagnosed in a Hawaiian population of Penaeus stylirostris in 1987 and in Penaeus vannamei in 1989 (J. Brock, Hawaii Department of Land and Natural Resources, Aquaculture Development Program, personal communication, 1990~. The disease is also found virtually everywhere these species are cultured. Impacts of Feed Additives Antibiotics may be added to fish feed to reduce mortality from bacterial fish diseases such as vibriosis and furunculosis. These antibiotics are used in marine aquaculture as prophylaxis and as therapy for disease outbreaks. In other animal production operations, such as for cattle and pigs, antibiot- ics are frequently used on a continual basis to prevent disease and enhance growth (NAS, 19801. At present, only three antibiotics are approved for use during disease outbreaks on fish farms in the United States oxytetracycline (OTC), sulfamerazine, and Romet 30, a sulfa drug. Of these three, OTC is by far the most commonly used antibiotic. Concerns about antibiotics stem from three potential environmental ef- fects (Whitely and Johnstone, 1990~: 1. development of drug-resistant strains of bacteria, 2. accumulation of antibiotics in sediments and subsequent inhibition of microbial decomposition, and 3. accumulation of antibiotics in fish and shellfish. The first two concerns are based on actual occurrences under specific conditions. Aoki and Kitao (1985) found drug-resistant bacteria in the ef- fluent of an intensive culture fish pond in Japan. Jacobsen (1989) reported OTC in the sediments beneath net pens in Norway, and drug resistance was transferred from a fish pathogen to a human pathogen in vitro and at tem- peratures as high as 36°C (Toranzo et al., 1984~. The frequency of drug-resistant bacteria does increase as a result of antibiotic use in animal feed, and this resistance can be transferred to hu-
OCR for page 107
ENVIRONMENTAL ISSUES 107 man and animal pathogens (Wright, 1990~. However, the evidence remains circumstantial that human health is threatened even under the continual use of antibiotics in livestock operations over many years (Walton, 19881. Ma- rine fish culturists in the United States use antibiotics only on a limited basis. For example, net-pen growers may use OTC for two or three treat- ments of 10 days each during the year. Antibiotics are used only when necessary. Accumulation of an antibiotic in sediment depends on many factors, including its solubility, half-life, and concentration in seawater. OTC is highly soluble in seawater and has a short half-life (Jonas et al., 1984~. Austin (1985) calculated that under a worst-case scenario, the highest antibiotic levels in receiving waters would correspond to a dilution of 1:50,000,000. They concluded from this finding that the release of pharma- ceutical compounds from fish farms was unlikely to pose an environmental problem. Several studies have demonstrated that shellfish did not accumulate anti- biotics in their tissue above the concentration in the surrounding water (NAS, 1980; Tibbs et al., 19881. A fourth concern about antibiotics is the possible impact on human con- sumers from antibiotic residues in fish. The risk is greater for imported fish because the kinds of antibiotic treatments and their duration on U.S. fish farms are regulated more stringently in the United States than elsewhere. The time during which antibiotic residues remain in trout muscle depends largely on water temperature. For salmonids given OTC, recommended withdrawal times are 60 days at a water temperature of 12°C and 90 days at 6°C (Jacobsen, 1989~. At present, no inspection procedures are in place for imported fish, but cooking destroys most OTC residues in salmonids (Herman et al., 1969~. Little information is available on clearance times and residues in nonsalmonid farmed fish. More understanding is needed of the potential deleterious effects on the environment from treatment of disease in the culture operation (e.g., pesticide treatment for fish lice in- festment in net pens). The Food and Drug Administration (FDA) has recently adopted a strin- gent policy on the use of unapproved drugs in aquaculture, a policy that could have profound impact on standard aquaculture practices. The policy requires producers and researchers to obtain approval from FDA for investi- gational use before they can use any drug not formally approved. The process for obtaining formal approval of a drug is likely to involve a time- consuming and expensive process. The FDA points out that current federal and state funding for drug development research is inadequate to meet the needs of the aquaculture industry, and suggests that congressional appro- priations be allocated for this endeavor (Water Farming Journal, 1991~.
OCR for page 108
108 MARINE AQUACULTURE ENVIRONMENTAL REQUIREMENTS OF MARINE AQUACULTURE Marine aquaculture has as a basic environmental requirement, accessible water of suitable temperature, quality, and quantity. Varying amounts of water exchange are necessary, depending on the species. Also of impor- tance is the selection of a site where stock can be protected from weather extremes and from human or animal interference. Marine aquaculture is highly vulnerable to external pollution by domestic and industrial wastes, oil and chemical spills, and other discharges that may originate from sources remote from the culture operation but be carried to it by tides and currents. The discharge of toxic industrial waste is a hazard to marine aquaculture because shellfish and seaweed are particularly vulnerable to heavy-metal pollution as well as to pollution from synthetic organic compounds. The cultured organism can concentrate mercury, lead, cadmium, arsenic, poly- chlorinated biphenyls (PCBs), and other toxic compounds to such an extent that it is altered, killed, or rendered unsafe for human consumption. By far, the greatest impact on aquaculture from pollution, however, has been the closure of both natural and cultivated shellfish beds due to pollu- tion from animal and human wastes. The nutrients in domestic wastewater, whether it is treated or untreated, also may induce blooms of toxic or otherwise harmful algae, for example, by increasing the concentrations of primary nutrients (inorganic nitrogen, phosphorus), and through organic overloading. Mollusks Shellfish aquaculture requires approved (waste-free) marine or brackish water with suitable food organisms, specific depths and temperatures, and low turbidity. Sites are limited because shellfish are vulnerable to external pollution by industrial, municipal, and agricultural wastes owing to their feeding habits. Major closures of both natural and cultivated shellfish beds have been caused by the presence of bacteria from domestic sewage. This problem has resulted in the elimination of one-half or more potential culture sites in many regions, including the Chesapeake Bay and San Francisco Bay. Closures are also caused by nonpoint sources of pollution. For ex- amp~e, many locations have enforced automatic closures after rainfalls of preset intensity and duration. In addition, shellfish may also become contaminated with poisons by ingesting toxic microorganisms from the water, which makes them unsafe for human consumption due to the danger of paralytic shellfish poisoning (PSP). In California, a mussel watch program that includes participation by
OCR for page 109
ENVIRONMENTAL ISSUES 109 aquaculturalists monitors for toxic conditions to regulate closure of public gathering grounds as well as to suspend harvest at culture facilities. Another concern is the possible transfer of human pathogens from pol- luted growing water to the shellfish and then from the shellfish to humans who eat them raw. Pathogens of concern are polio, hepatitis A, and Norwalk viruses, as well as Vibrio spp. and other enteric bacterial pathogens (Richards, 19881. Such pathogens generally originate in domestic wastewater. The current standard used for monitoring shellfish and culture waters for the purpose of public health protection is recognized as inaccurate and inad- equate. The fecal coliform test does not measure the relevant microorgan- isms (viral and bacterial pathogens) and does not provide a useful index of sewage pollution. Fecal coliforms have been found to reproduce in the aquatic environment and are produced and released by aquatic birds, do- mestic animals, and wildlife, as well as by humans (IOM, 19911. Finfish and Shrimp Marine finfish farms in the United States are located nearshore (cages) or onshore (tanks, raceways, and ponds). Species requirements sharply limit the number of suitable sites. For example, a site for salmon cages must have unpolluted water at least 10 m deep, a water temperature of 0- 18°C, current between 10 and 100 centimeters per second, and protection from severe weather. A site for culture of red drum or shrimp requires a location where seawater can be effectively pumped to the facility. Prices of suitable land are generally determined by residential or commercial inter- ests, which limit the economic feasibility of an aquaculture operation. Regu- latory constraints on aquaculture effluents also present major problems in site selection. For example, many miles of coastline in Hawaii are zoned to prohibit discharges of any kind (Ziemann et al., 1990~. For anadromous fish, large amounts of fresh water are usually required in early life stages. Hatchery sites for anadromous finfish on the West Coast are limited, and there are restrictions on groundwater use in the lower Mississippi delta and the Atlantic coastal plain. Seawater intrusion into freshwater aquifers is becoming more prevalent, resulting in increased re- strictions on the use of water from these aquifers. RESOLVING ENVIRONMENTAL PROBLEMS In some cases, the mitigation of environmental problems associated with marine aquaculture may be possible through improved understanding of biological and ecological factors involved in culturing various marine spe- cies, and through engineering and technology solutions that allow new ap- proaches to siting and to culture operations. These options are explored in
OCR for page 110
110 MARINE AQUACULTURE detail in Chapter 5. Some of the state and federal policy issues discussed in Chapter 3 are also relevant to environmental issues, and changes in manage- ment and regulatory approaches may alleviate environmental controversies. The aspects of environmental issues that involve public attitudes and values may be addressed through active efforts at educating both the public and policymakers about the benefits of aquaculture and the prospects for alleviating some of the most serious environmental impacts. Solutions to the environmental problems constraining marine aquaculture will involve approaches that combine technological "fixes" with improved regulatory and management structures, as well as public education about the value of marine aquaculture to the nation. REFERENCES Aoki, T., and T. Kitao. 1985. Detection of transferable R plasmids in strains of the fish-pathogenic bacterium Pastuerella piscicida. Journal of Fish Diseases 8:345- 350. Austin, B. 1985. Antibiotic pollution from fish farms; Effects on aquatic microflora. Microbiological Sciences 2(4~:113-117. Browdy, C.L., J.R. Richardson III., C.O. King, A.D. Stokes, J.S. Hopkins, and P.A. Sandifer. 1990. IHHN virus and intensive culture of Penaeus vannamei: Effects of stocking and water exchange rates on production and harvest size distribution. World Aquaculture Society, World Aquaculture 90, Abstract T17.3. Brune, D.E. 1990. Reducing the environmental impact of shrimp pond discharge. American Society of Agricultural Engineers, ASAE Paper No. 90-7036. St. Joseph, Mich. Brune, D.E., and C.M. Drapcho. 1991. Fed pond aquaculture. Pp. 15-33 in Aquaculture Systems Engineering: Proceedings of the World Aquaculture Society and Amer- ican Society of Agricultural Engineers Jointly Sponsored Session. American Society of Agricultural Engineers, St. Joseph, Mich. Burrell, V.G., Jr. 1985. Oyster culture. Pp. 235-273 in Crustacean and Mollusk Aquaculture in the United States, J.V. Huner and E.E. Brown, eds., Westport, Conn: AVI Publishing Co. Campbell, J.W. 1973. Nitrogen excretion. In Comparative Animal Physiology, C.L. Prosser, ed. Philadelphia, Pa.: W.B. Saunders. Chamberlain, G.W. 1986. 1985 Growout research. Coastal Aquaculture 3(2~:7-8. Chamberlain, G.W. 1991. Status of shrimp farming in Texas. Pp. 36-57 in Shrimp Culture in North America and the Caribbean, P.A. Sandifer, ed. Baton Rouge, La.: The World Aquaculture Society. Chesapeake Bay Program. 1991. Report and recommendation of the Non-point Source Evaluation Panel, CPB/TRS 56/91. Annapolis, Md. Chew, K.K. 1990. Global bivalve shellfish introductions. Journal of the World Aquaculture 2 1~3~:9-22. Colt, J.E., and D.A. Armstrong. 1981. Nitrogen toxicity to crustaceans, fish and mollusks. In Proceedings of the Bio-Engineering Symposium for Fish Culture,
OCR for page 111
ENVIRONMENTAL ISSUES 111 L.J. Allen and E.C. Kinney, eds. Fish Culture Section, American Fisheries Society Bethesda, Md. Courtenay, Jr., W.R. Regulation of aquatic invasives in the United States of America with emphasis on fishes. Unpublished manuscript. Cross, S.F. 1990. Benthic impacts of salmon farming in British Columbia. Report to the British Columbia Ministry of the Environment, Water Management Branch, Victoria, B.C. 78 pp. Daniels, H.V., and C.E. Boyd. 1989. Chemical budgets for polyethylene-lined, brackish water ponds. Journal of the World Aquaculture Society 20~2~:53-60. Dixon, I. 1986. Fish Farm Surveys in Shetland: Summary and Survey Reports, Vol. 1. A report to NCC, Shetland Islands Council and Shetland Salmon Farmers Assoc. FSC/OPRU/30/80. Orielton Field Center, Pembroke, Dyfed, Scotland. Ellis, M. 1990. Decomposition processes on the pond bottom. Presented at Texas Aquaculture Conference, Corpus Christi, Tex. February. Figueras, A.J. 1989. Mussel aquaculture in Spain and France. World Aquaculture 20(4):8- 17. Food and Agriculture Organization (FAO). 1977. Control of spread of major communicable fish diseases. Report of the FAO/OIE Government Consultation on an International Convention for the Control of the Spread of Major Communi- cable Fish Diseases. FAG Fisheries Reports, No. 192. FID/R192 (EN). Gillespie, D. 1986. An inquiry into finfish aquaculture in British Columbia: Report and recommendations. Prepared for Government of British Columbia, December. 50 pp. Gowen, R.J., and N.B. Bradbury. 1987. The ecological impact of salmon farming in coastal waters: A review. Oceanography and Mar. Biol. Annual Rev. 25:562-575. Gowen, R.J., and D.S. McLusky. 1990. Investigation Into Benthic Enrichment, Hypernutrification and Eutrophication Associated With Mariculture in Scottish Coastal Waters. Summary of main report of Highlands and Islands Develop- ment Board, National Conservation Council and Scottish Salmon Growers Assoc., 13 pp. Gowen, R.J., and H. Rosenthal. 1990. Presentations to the committee. Halifax, Nova Scotia, June 11 - 15. Griffiths, R.W., D.W. Schlaesser, J.H. Leach, and W.P. Kovolak. 1991. Distribu- tion and dispersal of the zebra mussel (Dreissena polymorpha) in the Great Lakes Region. Canadian Journal of Fisheries and Aquatic Sciences 48:1381-1388. Herman, R.L., D. Collis, and G.L. Bullock. 1969. Oxytetracycline residues in dif- ferent tissues of trout. Burl Sport Fish. and Wildlife. Tech Paper No. 37. U.S. Department of the Interior. Washington, D.C. Hetrick, J. 1991. Alaskan Aquaculture. Water Farming Journal 6~4~:(April)10-13. Hicks, B. 1989. Fish health regulations restrict industry not disease. Can. Aqua- culture 6(1):27-28. Hindar, K., N. Ryman, and F. Utter. 1991. Genetic effects of aquaculture on nat- ural fish populations. Can. J. Fish. Aquat. Sci. 48:945-957. Hopkins, J.S. 1991. Status and history of marine and freshwater shrimp farming in South Carolina and Florida. Pp. 17-35 in Shrimp Culture in North America and the Caribbean, P.A. Sandifer, ed. Baton, Rouge, La.: The World Aquaculture Society.
OCR for page 112
2 MARINE AQUACULTURE Hopkins, J.S., M.L. Baird, O.G. Grados, P.P. Maier, P.A. Sandifer, and A.D. Stokes. 1988a. Impact of intensive shrimp production on the culture pond ecosystem. Journal of the World Aquaculture Society 19 ~ 1 ~ :37A (abstract). Hopkins, J.S., M.L. Baird, O.G. Grados, P.P. Maier, P.A. Sandifer, and A.D. Stokes. 1988b. Impacts of Intensive Shrimp Culture Practices on the Culture Pond Ecology. Report from the Waddell Mariculture Center, of the South Carolina Marine Re- sources Division. Charleston, S.C. Hopkins, J.S., A.D. Stokes, C.L. Browdy, and P.A. Sandifer. Submitted. The relationship between feeding rate, paddlewheel aeration rate and expected dawn dissolved oxygen in intensive shrimp ponds. Aquacultural Engineering. Institute of Medicine (IOM). 1991. Seafood Safety. Washington, D.C.: National Academy Press. International Council for Exploration of the Seas (ICES). 1984. Guidelines for implementing the ICES code of practice concerning introductions and transfers of marine species. Copenhagen: ICES Cooperative Res. Rep. 130, 1-20. International Council for Exploration of the Seas (ICES). 1988a. Report of the ad hoc study group on environmental impacts of mariculture. Copenhagen: ICES Cooperative Res. Rep. 164, 83 pp. International Council for Exploration of the Seas (ICES). 1988b. Report of the Work- ing Group on Environmental Impacts of Mariculture. Hamburg, Germany, April. Jacobsen, M.D. 1989. Withdrawal times of freshwater rainbow trout, Salmo gairdneri, after treatment with oxolinic acid, oxytetracycline and trimetoprim. J. Fish Diseases 12:29-36. Jonas, M., J.B. Comer, and B.A. Cunha. 1984. Tetracyclines. In Antimicrobial Therapy, A.M. Ristuccia and B.A. Cunha, eds. New York: Raven Press. Kalagayan, G., D. Godin, R. Kanna, G. Hagino, J. Sweeney, and J. Wyban. 1990. IHHN virus as an etiological factor in runt-deformity syndrome of juvenile Penaeus vannamei cultured in Hawaii. World Aquaculture Society, World Aquaculture 90, Abstract T 17.2. King, S.T., and J.R. Schrock. 1985. Controlled Wildlife Vol. III: State Wildlife Regulations. Lawrence, Kan.: Association of Systematics Collections. Krom, M.D., C. Porter, and H. Gordin. 1985. Nutrient budget of a marine fish pond in Eilat, Israel. Aquaculture 51: 65-80. Lightner, D.V. 1990. Viruses section: introductory remarks. Pp. 3-6 in Pathology in Marine Science. New York: Academic Press. Lutz, R.A. 1985. Mussel aquaculture in the United States. Pp. 311-363 in Crustacean and Mollusk Aquaculture in the United States, J.V. Huner and E.E. Brown, eds. Westport, Conn.: AVI Publishing Co. Manzi, J.J. 1985. Clam aquaculture. Pp. 275-310 in Crustacean and Mollusk Aquaculture in the United States, J.V. Huner and E.E. Brown' eds. Westport, Conn.: AVI Publishing Co. Mathisen, O.A., and T. Gudjonsson. 1978. Salmon management and ocean ranch- ing in Iceland. J. Agr. Res. Iceland 10~21:156-174. McLaughlin, T.W. 1981. Hatchery effluent treatment U.S. Fish and Wildlife Service. In Proceedings of the Bio-Engineering Symposium for Fish Culture, L.J. Allen and E.C. Kinney, eds. Fish Culture Section, American Fisheries Society, Bethesda, Md.
OCR for page 113
ENVIRONMENTAL ISSUES 113 Mudrak, V.A. 1981. Guidelines for economical commercial fish hatchery wastewater treatment systems. In Proceedings of the Bio-Engineering Symposium for Fish Culture, L.J. Allen and E.C. Kinney, eds. American Fisheries Society, Bethesda, Md. Munro, A.S.S., and I.F. Wadell. 1984. Furunculosis: Experience of its control in the sea water cage culture of Atlantic salmon in Scotland. ICES CM/F:32. 9 pp. National Academy of Sciences (NAS). 1980. The Effects on Human Health of Subtherapeutic Use of Antimicrobials in Animal Feeds. Committee to Study the Subtherapeutic Antibiotic Use in Animal Feeds. Washington, D.C.: National Research Council. Nehlsen, W., E. Williams, and J.A. Lichatowich. 1991. Pacific salmon at the crossroads: Stocks at risk from California, Oregon, Idaho, and Washington. Fisheries 16(2~:4-21. North Atlantic Salmon Conservation Organization (NASCO). 1990. Report on the Norwegian meeting. Loen, Norway, May. Nose, T. 1985. Recent advances in aquaculture in Japan. Geojournal 10(3~:261- 276. Paramatrix, Inc. 1990. Final programmatic environmental impact statement: Fish culture in floating net pens. Prepared for the Washington Department of Fisheries, Olympia, Wash. Porter, C., M.D. Krom, M. Robbins, L. Brickell, and A. Davidson. 1987. Ammonia excretion and total N budget for gilthead seabream (Sparus aurata) and its effect on water quality conditions. Aquaculture 66: 287-297. Pruder, G.D. 1991. Shrimp culture in North America and the Caribbean: Hawaii 1988. Pp. 58-69 in Shrimp Culture in North America and the Caribbean, P.A. Sandifer, ed. Baton Rouge, La.: World Aquaculture Society. Richards, G.P. 1988. Microbial purification of shellfish: A review of depuration and relaying. J. Food Protection 51(3): 218-251. Rosenberry, R. 1990. Shrimp farming in the Western Hemisphere. Presented at Aquatech 90, Malaysia, June. Rosenfield, A., and F.G. Kern. 1979. Molluscan imports and the potential for introduction of disease organisms. Pp. 165-89 in Exotic Species in Mariculture, R. Mann, ed. Cambridge, Mass.: MIT Press. Rosenthal, H. 1980. Implications of transplantations to aquaculture and ecosystems. Marine Fisheries Review 42~51:1-14. Rosenthal, H. 1985. Constraints and perspectives in aquaculture development. GeoJournal 10(31:305-324. Sandifer, P.A. 1988. Aquaculture in the West: World Aquaculture Society 19(21:73-84. Salser, B., L. Mahler, D. Lightner, J. Ure, D. Danald, C. Brand, N. Stamp, D. Moore, and B. Colvin. 1978. Controlled environment aquaculture of penaeids. In Drugs and Food From the Sea, Myth or Reality? P.M. Kaul and C.J. Sindermann, eds. Norman, Okla.: University of Oklahoma Press, Sandifer, P.A., J.S. Hopkins, A.D. Stokes, and C. Browdy. Submitted. Preliminary comparisons of the native (Penaeus setiferus) and Pacific (P. vannamei) white shrimp for pond culture in South Carolina. Sandifer, P.A., J.S. Hopkins, A.D. Stokes, and G.D. Pruder. 1991a. Technological A Perspective. Journal of the
OCR for page 114
114 MARINE AQUACULTURE advances in intensive pond culture of shrimp in the United States. Frontiers of Shrimp Research. Elsevier. New York, N.Y. Sandifer, P.A., A.D. Stokes, and J.S. Hopkins. 1991b. Further intensification of pond shrimp culture in South Carolina. In Shrimp Culture in North America and the Caribbean, P.A. Sandifer, ed. World Aquaculture Society. Sattaur, O. 1989. The threat of the well-bred salmon. New Scientist 29 (April):54- 58. Saunders, R. L. 1988. Algal catastrophe in Norway. World Aquaculture 19~3~:11-12. Seter, R.M. 1990. Potential within aquaculture issues of the use of genetic engineering and of the introduction of species. Unpublished manuscript. College of Marine Studies, University of Delaware. Shumway, S.E. 1990. A review of the effects of algal blooms on shellfish and aquaculture. Journal of the World Aquaculture Society 21~2~:65-104. Sindermann, C.J. 1988. Disease problems created by introduced species. Pp. 394- 98 in Disease Diagnosis and Control in North American Marine Aquaculture, 2nd ea., C.J. Sindermann and D.V. Lightner, eds. Amsterdam: Elsevier. Thompson, A.G. 1990. The danger of exotic species. World Aquaculture 21~3~:25- 32. Tibbs, J.F., R.A. Elston, R.W. Dickey, and A.M. Guarino. 1988. Studies on the accumulation of antibiotics in shellfish. Northwest Environmental Journal 5~1~. Toranzo, A.E., P. Combarro, M.L. Lemos, and J.L. Barja. 1984. Plasmid coding for transferable drug resistance in bacteria isolated from cultured rainbow trout. Applied and Environmental Microbiology 48:872-877. Van Engel, W.A., W.A. Dillon, D. Zwerner, and D. Eldridge. 1966. Loxothylacus panopei (Cirripedia, Sacculinidae) an introduced parasite on a xanthid crab in Chesapeake Bay, U.S.A. Crustaceana 10:110-112. Vermeij, G.J. 1991. When biotas meet. Understanding biotic interchange. Science 253:1099-1103. Walton, J. R. 1988. Antibiotic resistance: An overview. Veterinary Record 122:247- 251. Waples, R.S., G.A. Winans, F.M. Utter, and C. Mahnken. 1990. Genetic approaches to the mana~ement of Pacific salmon. Fisheries 15(5):19-25. ~ . . . . ~ Water Farming Journal. 1991. FDA adopts tough new policy on use of drugs in aquaculture. (September 28~:4-6, 27. Weston, D.P. 1986. The environmental effects of floating mariculture in Puget Sound. School of Oceanography, College of Ocean and Fishery Science, University of Washington, Seattle. 148 pp. Weston, D.P. 1991. The effects of aquaculture on indigenous biota. Pp. 534-567 in Aquaculture and Water Quality, D.E. Brune and J.R. Tomasso, eds. Baton Rouge, La.: World Aquaculture Society. Weston, D.P., and R.J. Gowen. 1988. Assessment and prediction of the effects of salmon net-pen farming on the benthic environment. Report to Washington De- partment of Fisheries, Olympia, Wash. 62 pp. Whetstone, J.M., E.J. Olmi III, and P.A. Sandifer. 1988. Management of existing saltmarsh impoundments in South Carolina for shrimp aquaculture and its impli- cations. Pp. 327-338 in The Ecology and Management of Wetlands, D.D. Hook et al., eds. Portland, Ore.: Timber Press.
OCR for page 115
ENVIRONMENTAL ISSUES 115 Whiteley, A.H., and A. Johnstone. 1990. Additives to the environment of net-pen reared fish. Proc. Pacific Marine Fisheries Commission 42nd Annual Meeting, Seattle, Wash., October 16-18, 1989. Wright, K. 1990. Bad news bacteria. Science 249:22-24. Wyban, J.A., and J.N. Sweeney. 1991. Intensive Shrimp Production Technology; the Oceanic Institute Shrimp Manual. Hawaii: The Oceanic Institute. 158 pp. Ziemann, D., G.D. Pruder, and J.K. Wang. 1990. Honolulu, Hawaii: University of Hawaii. Aquaculture Effluent Discharge Program, Center for Tropical and Sub- tropical Aquaculture, Year 1 Final Report.
Representative terms from entire chapter: