Aquaculture is the fastest growing sector of US agriculture, and for good reason. Aquaculture’s phenomenal growth and bright prospects can be attributed to an increasing demand for consistent, high-quality wholesome products by American consumers. Additional aquaculture demand is created because many wild stocks have been diminished by over fishing or environmental changes. The challenge for aquaculture is to continue to deliver high quality product while maintaining profitability and environmental compatibility.
Many different kinds of aquatic animals and plants are raised commercially in the US and more are being tested for production potential. This is important because Americans are given medical advice to eat more fish yet are faced with a static base of mostly imported expensive products. In the US, aquaculture is often thought of as a single industry but it is important to realize the industry contains a variety of species each with unique production requirements, challenges and varying potential to impact the environment. Our land based animal industry is composed of a variety of species (e.g., poultry, cattle and sheep) that share a common production feature, that being land. The aquaculture industry with its variety of species shares a common feature as well, water. Aquaculture, depending upon the type of plant or animal reared, uses either fresh, brackish or salt water.
The largest and most prominent aquaculture sectors in the US (listed according to pounds raised) are catfish, oysters, trout, crawfish, salmon, clams, tilapia, striped bass, baitfish, and ornamental fishes. Each of these industry sectors have developed over the past 30 to 50 years and, with the exception of baitfish and ornamentals, are generally directed at production for human consumption. The catfish sector is by far the largest with total production exceeding 500 million pounds per year. The trout sector produces fish for human consumption and for stocking public waters for recreational uses. Approximately 25% of trout raised in the US are destined for fee fishing lakes as a source of recreation.
Aquaculture is used with varying success to conserve endangered fish populations or enhance over-fished populations. Federal and state agencies also produce a variety of fish, using aquaculture techniques, for stocking in public waters. Aquaculture is one of the most viable methods of supplying a growing world and US populations food needs. More recently developed commercial species include hybrid striped bass, marine shrimp and sturgeon. Considerable research is being directed at production of other species such as yellow perch, walleye, sea urchins, abalone, flounder and cod to name a few. Each of these specie specific sectors is successful or has the potential to succeed because of American consumer demand. In short, American consumers enjoy eating fishery products, whether caught or bought.
While US aquaculture continues to grow, it is also challenged by ever increasing competition for resources, a burgeoning population, continued urbanization, competition from foreign products not subject to US regulations, and a wealth of misinformation. Legitimate concerns about aquaculture’s environmental impact are sometimes raised, just as there are with all other types of human or domesticated animal impacts. Concerns raised must be founded on fact and credible analysis as credibility is dependent upon facts. The recently released Environmental Defense Fund "Murky Waters" report contains unsubstantiated innuendo, extrapolates from isolated incidents in the US or from outside the US and contains erroneous information. Unfortunately, use of innuendo, misinformation or uninformed emotional arguments by advocacy groups leads to polarization, lack of progress, and diversion of resources away from more significant issues.
US aquaculture is not, in most cases, the same as aquaculture in other parts of the world. Aquaculture in the US is under close scrutiny from regulatory agencies including the Environmental Protection Agency (EPA), the Food and Drug Administration (FDA), the National Marine Fisheries Service (NMFS), the United States Department of Agriculture (USDA), the US Fish and Wildlife Service (USFWS), and numerous state environmental agencies. There is also an unprecedented societal environmental awareness and activism. As our knowledge about ecosystems and watershed management improves, appropriate action by all parties can be taken to ensure sustainability. For example, it is now recognized that to protect the integrity of our water resources, a watershed approach is necessary. If the control focus is on just one element, public policies may be developed that aggravate watershed problems rather than contribute to restoration or sustainability.
Aquaculture practices of the past, both in the US and in many places throughout the world, have changed and are continuing to improve. Production practices are most often determined by the availability of natural resources and various social and economic constraints. As our knowledge about production efficiency has increased, environmental stewardship has ensued. The best actions have often been voluntary. The current regulatory system helps ensure US aquaculture continues to be compatible with state and federal water quality requirements and is compatible with watershed management plans. Before any new regulations are instituted it is essential that existing environmental requirements be applied. This paper examines many of the environmental issues affecting the various US aquacultured species. Aquaculture has been responsive to societal needs and continually develops and applies credible, scientifically sound information throughout the public and commercial domain. With this information, aquaculture can continue to prosper, remain compatible with the environment and benefit the American public.
The US aquaculture industry is developing in an unprecedented environmental and food safety climate. In many respects, this helps ensure the aquaculture industry is environmentally sustainable, while still providing needed rural employment and income. This situation also places a unique challenge upon aquaculture because it must experiment with new species production techniques under close scrutiny. Most other forms of agriculture developed over the past 200 to 300 years and became profitable prior to current constraints. Nevertheless, aquaculture is thriving because it can fit the environmental, social, and economic needs of the communities where it is located.
Clean Water Act (CWA) programs provide regulatory oversight to ensure discharges from aquaculture facilities are compatible with the environment. Because many forms of aquaculture are considered point sources, each source must be covered by a National Pollutant Discharge Elimination System (NPDES) permit. Discharge permits are developed by a state’s environmental regulatory agency or by the EPA if the state does not have permitting primacy. Permits developed by EPA must receive a state’s approval (401 certification) indicating the federally permitted discharge will comply with the applicable provisions of the CWA and state water quality standards will not be violated. It is incumbent on the state or the federal government to adequately enforce existing environmental requirements since these are often adequate to meet environmental quality standards.
Concerns about human impacts on water quality are prevalent throughout the US. Many water bodies (not impacted by aquaculture operations) throughout the US have been declared "water quality limited" signifying failure of a water body to satisfy water quality standards and attainment of full designated beneficial uses. For these water bodies, a total maximum daily load (TMDL) is developed. The TMDL attempts to limit pollutants from both point and non-point sources depending upon what a particular water body can assimilate and still meet standards. This is called the water bodies assimilative capacity. Assimilative capacity is determined by a number of physical, chemical and biological factors. Physical factors include river or lake water volume, flow rate management, and sediment volumes. Chemical factors may include nutrient levels (such as phosphorus) and toxic chemicals from industrial discharges. Biological factors include plant composition and abundance, and fish composition. Because these characteristics are peculiar to each water body, the assimilative capacity for each is determined on a site specific basis. National standards must reflect the site specific nature, the integration of these processes and allow considerable flexibility in implementation.
Maintenance and improvement of water quality to meet the fishable and swimmable goals of the Clean Water Act require everyone’s involvement. This is in recognition that both point (e.g. factories) and non-point sources (e.g. farms and other diffuse pollution sources) as well as hydromodifications such as dams and channelization, all impact water quality and the ecosystem. Recent presidential initiatives (i.e., the Clean Water Initiative) identify non-point pollutant sources as a significant cause of reduced water quality in 70 % of impaired rivers and streams, and 49 % of lakes.
Food safety efforts may also benefit the environment. The FDA has recently (Dec. 1997) instituted a mandatory processor seafood safety program. This program relies on the Hazard Analysis Critical Control Point (HACCP) process to help ensure all seafood’s are wholesome for consumers. As part of this program, aquaculturists must ensure their use of therapeutants for aquatic animals are safe. The FDA also carefully scrutinizes drugs to ensure they are safe for the environment before they are approved for use. This is in compliance with the Federal Food, Drug and Cosmetic Act. Any water treatments or algaecides used by an aquaculturist must be approved by the EPA and are regulated under the NPDES permit system. Compounds approved for use by US aquaculturists are listed in the document "Guide to Drug, Vaccine and Pesticide Use in Aquaculture" written in 1994 by the Quality Assurance Working Group of the federal Joint Subcommittee on Aquaculture. This document is currently being revised.
Water (Rearing) Environments
Each aquatic species has specific environmental requirements. The various salmonids (salmon and trout) for example require cold (50-60° F), highly oxygenated waters (oxygen greater than 6 mg/L), but the water can be fresh or salt water. Catfish are grown in fresh water but can tolerate a wide variety of water temperatures growing best at water temperatures above 75°F with oxygen concentrations above 4 mg/L. Marine mollusks, such as oysters, and crustaceans, such as shrimp, must be grown in water where salt (NaCl) levels are higher and where the water is saturated with oxygen.
In all cases, waters used in aquaculture production must be free of compounds that could contaminate or taint the flesh. These waters must obviously be free of anything that could cause aquatic animal mortality. Aquaculturists strive to protect their rearing waters from contaminates. As part of industry-developed HACCP programs, rearing areas and influent waters are tested for pesticides or other contaminants. Because the environment of many aquacultured animals is controlled and protected from contaminants, animals raised under these conditions are typically free of contaminants. FDA records as well as university research surveys of aquacultured animals demonstrates farm raised aquatic animals are generally free of harmful chemicals. Aquaculture is a water dependent industry. Aquaculturists must be good stewards of water use, our success depends on it.
The FDA instituted a mandatory seafood processors safety program to ensure that the US consumer continues to receive safe wholesome seafood. This program relies upon a HACCP plan and is enforced by seafood processors but inspected by FDA. The National Aquaculture Association (NAA) endorses this program and has been instrumental in developing various aquaculture producer quality assurance programs. Environmental quality is identified in these plans as an important factor needed to ensure wholesome aquatic animals.
Another reason for aquaculture’s environmental sustainability is its minimal use or consumption of water. Globally and within the US, water is a precious resource. Minimal consumption is important because conflicts over availability are expected to increase dramatically over the next several decades. Contrary to common perception, aquaculture has minimal water consumption.
Water used by aquaculture operations is generally returned back to the environment after some brief period of use. For example, in Idaho, where most US trout production occurs, gravity fed, naturally flowing spring water is diverted into cement raceways holding trout. The water flows through the raceways after which it is treated to remove solid wastes and then discharged into the Snake River. The water is not consumed or used up in the production process nor does it deplete the aquifer.
In the western part of the US, use of water (whether for irrigation purposes, home use or for aquaculture) is contingent upon having a valid water right. Western states rely upon the prior appropriation doctrine that stipulates that the individual claiming use of water first in time will be able to use the water before a more junior water right holder can use the same water. These water rights are called usufructuary rights indicating that while the water belongs to the state, the water can be rightfully used for beneficial purposes by a private individual. The state determines validity of water rights and otherwise manages use of this resource. The water must be put to beneficial use for the usufructuary right to be maintained. Similarly, net pens commonly used for salmon production in the northeast or northwest US do not consume water. Oysters and clams simply filter the water that passes over them. In many states, aquaculture has been legally classified as a beneficial, nonconsumptive, use of water.
In some aquaculture situations water is indeed consumed but this is usually minimal and is due to evaporation. Catfish ponds can lose water during the summer due to evaporation. This water is replaced by precipitation throughout the year so that in any one year, a net gain or loss of water might occur depending upon prevailing climatic conditions. Appropriate pond water level management can minimize the need for adding water. Some aquaculturists discharge their effluent onto fields for irrigation or nutrient control, thus integrating well with existing agriculture. This practice is minimal in most areas because there is insufficient land for such discharge or the cost of pumping the water is prohibitive.
Aquaculturists using semi-closed or closed recirculating systems often need to add new fresh water to ensure appropriate rearing environments and to replace water lost to evaporation. These intensive production systems are generally more expensive to operate and more technically demanding than raceway, pond or net pen culture systems.
Water use on US shrimp farms has changed in recent years. Research suggests the frequent exchange of pond water with marine waters for supplemental aeration is unnecessary. The only additional waters needed are those to replace pond water lost to evaporation so that pond salinities do not become excessive.
Environmental Impacts of Discharge
Depending upon the aquaculture system, water may or may not be discharged into the environment. Pond aquaculturists, such as those farming catfish, striped bass, baitfish, or ornamental fishes typically do not discharge their waters. Evaporation water is replaced by precipitation or pumping from shallow wells. In these culture practices, discharge of water occurs mostly when ponds are completely drained for pond maintenance. This occurs infrequently on an as needed basis. Recirculating water production systems also discharge water regularly but only in very limited quantities. Concentrations of substances may be high, but total load may be quite low.
Raceway culture systems, such as occurs with salmonids , do routinely discharge water which may contain elevated (above influent water quality) quantities of nutrients such as phosphorus. The impact of these nutrients is site specific. In some cases, the impact of elevated nutrients is obscured by other factors such as elevated sediment deposition from non-point sources or hydromodifications such as dams. For example, managed river or hydropower schemes often result in a dramatic reduction in the frequency of large magnitude floods which are important for normal river ecosystem function. These factors alone can obscure the significance of elevated phosphorus. In some cases however, the nutrients from an aquaculture facility may cause eutrophication.
The impact of aquaculture operations must be determined within the context of a specific water body. Net pen culture, whether in a lake, reservoir or coastal marine area must also be evaluated within a site-specific context. Normal current actions may minimize the potential impact of a specific facility or group of facilities. In all cases, careful evaluation must be made based on site specific evaluations and allow for corrective action to be taken.
Aquatic Animal Feeds
Aquatic animal feeds are specially formulated to ensure economically optimal aquatic animal growth. Feeds are increasingly being formulated to minimize environmental impact. These advances have resulted in the manufacture of feeds that are high in energy and nutrient-dense. This has resulted in improved feed conversion efficiencies (amount of feed to produce one pound of animal) and less waste discharge. This increased attention to feed conversion coupled with the fact that aquatic animals in general are far more efficient at feed conversion than terrestrial animals, has yielded conversions at nearly 1:1 in some species.
An important ingredient in some aquatic animal feeds is fish meal. Fish meal is produced from various pelagic fishes that, with some exception, are not normally consumed by humans. The fish that are caught to produce fish meal (menhaden and anchovy) are subject to quotas. Quotas are imposed by government agencies to ensure that fish stocks remain sustainable. Additional fish meal is produced from the "by-catch" of the fishing industry. By-catch is unwanted fish that are accidentally netted or caught in the process of fishing for higher value fish than is usually intended for human consumption. Most of this by-catch is currently discarded back into the ocean. While these particular pelagic species are typically not consumed by humans, as a fish meal, they form a significant part of the diet of many different kinds of animals (terrestrial and aquatic) which become human food (Table 1).
Some (commercially grown) aquatic animals grow well with feeds based primarily on plant materials. Catfish feed, for example, contains only 3-5 % fish meal but considerable quantities of soybean meal. Tilapia are planktivores that consume single celled algae and do not require any fish meal in their diets. Bivalve mollusks are filter feeders that utilize the natural foods present in the environment for their sustenance. Because domestication of aquatic species and food technology is a relatively young science, feed optimization has yet to occur. Fortunately, considerable private and university research is underway to provide enhanced feeds for aquaculture species use.
Pathogens and Disease Control
Farmed aquatic animals are subject to the same diseases that occur naturally in wild aquatic animals. Unfortunately, knowledge about the interaction between pathogens of wild aquatic animals and aquacultured animals is poor. Because aquacultured animals receive considerably more scrutiny than their wild counterparts, more is known about diseases under aquaculture conditions.
Wild fishes are often the source of pathogens causing disease in domesticated species. There are several protozoan parasites, for example, that are resident or endemic in wild fish. These fish may seed parasites into the water that supply an aquaculture facility. The cause of "Ich" ( Ichthyopthirius multifiliis ) is a classic example. Almost anyone who has a home aquarium has seen Ich breakout when a new fish or aquarium plant is brought in. Birds or other animals may seed the facility with a new pathogen. Similar concerns occur in agriculture where wild bison or elk may serve as a potential reservoir for the organisms causing brucellosis in hoofed domesticated animals. It is because the aquacultured animals are closely confined, that disease may move through a population quickly.
The US Fish and Wildlife Service (USFWS) has recently set out to determine the prevalence of various fish pathogens in wild fish populations. This effort is required to increase knowledge about the interaction of aquatic animal pathogens between wild and aquacultured animals and provide a better accounting of where pathogens occur naturally. The NAA supports these efforts.
Treatment of aquatic animal diseases is difficult. The FDA closely regulates availability of drugs used by aquaculturists. There are only two antibacterial drugs available (Terramycin® and Romet-30®) in the US and these cannot be used for all aquatic species. Several microbicides can be used by aquaculturists including salt (NaCl), iodine (to treat eggs), and copper (EPA approved to treat algae). It is incumbent on each aquaculturist to use these compounds according to state or federal toxics criteria. Various efforts are underway, supported by the FDA, USDA, public and commercial interests to alleviate the lack of drugs or chemicals, but it is a formidable task. The high cost of drug approval is a significant barrier and there is a considerable disparity in the availability of aquatic animal drugs between the US and other countries. Additional efforts are being directed at harmonizing use of drugs internationally. These efforts are being encouraged by the FDA and the NAA. Because drugs should only be used as a last resort, enhanced husbandry (integrated fish health management) and vaccination of aquatic animals against specific pathogens are used for disease prevention. The NAA supports additional efforts directed toward these important farming practices.
The commercial aquaculture industry is concerned about the importation of exotic pathogens into the US. Current regulation of imported animals, including pathogens, under 50 CFR Part 16 and the Lacey Act may not be adequate to protect our resources nor to foster US aquaculture. The NAA, in association with the National Association of State Aquaculture Coordinators (NASAC), is coordinating efforts to further minimize the importation of injurious pathogens. These two groups are working closely to help establish a coherent national aquatic animal health management program. The commercial aquaculture industry expects to work closely with the US Department of Agriculture Animal Plant Health Inspection Service (USDA-APHIS) and the Office of International Epizootics (OIE) in this effort.
Commercially reared aquatic animals can be subject to significant predation by a variety of animals. These include birds, seals, crabs, flatworms and starfish. The economic impact of this depredation is difficult to quantify with precision. The US catfish industry, in association with the USDA Wildlife Control Service estimates that in Mississippi, Alabama and Louisiana cormorants consume $10-30 million worth of commercially raised channel catfish per year. Other birds known to predate on commercially raised aquatic animals include great blue herons, black-crowned night herons, kingfishers and white pelicans.
As aquaculture has prospered, so have various fish-eating birds. In some areas, according to natural resource managers, these birds have increased their numbers dramatically, far exceeding the normal carrying capacity of the area. The increased population of these birds has negatively impacted natural roosting areas and island habitats.
Both salmonid net pen culture and molluscan aquaculture operations have also been negatively impacted by depredation. Net pen salmonid aquaculture operations are subject to predation by seals (gray and harbor) and sea lions. The seals and sea lions cause net damage allowing fish to escape and they consume fish. Various burrowing shrimps invade oyster growing areas burrowing into the sand causing the oyster to sink and suffocate. Crabs consume large numbers of clam seed each year. Oysters are also subject to predation by starfish. The net loss and financial cost of these depredations have yet to be quantified but is significant.
Control of depredation is difficult and costly. Many trout farmers have completely covered their facilities with wire to prevent bird and other animals access. This method of deterrence can only be used where ice and snow are unlikely to damage the netting. More expansive production systems such as 10 to 20 acre catfish ponds or extensive shellfish beds are not suitable for covering and other methods to limit depredation must be developed. Some clam farms have been completely covered with mesh but this exacerbates fouling problems and is only partly effective. Clam farms on the US East Coast lose at least 30% or more of their planted seed due to predation. The various aquaculture species groups are working with the regulatory community to establish the best control methods possible. The NAA strongly supports this effort.
Exotic Animal Introductions
Introduction of exotic, non-native aquatic animals and plants into the US can, in some cases, cause significant ecological change. Past state and federal actions purposefully introduced exotic plants and animals into the US. Unfortunately, the positive or negative impacts of introductions are difficult to predict. Now, in spite of increased awareness, and a change in introduction philosophies, globalization of trade has increased the challenge of maintaining the biological integrity of the US and its waters.
Unintentional introductions of zebra mussel, green crab, and the Russian round goby occurred through release of ballast water from transcontinental ocean going ships. These aquatic animals are spreading throughout various regions of the US and in some cases, have caused significant harm.
Some imported animals have proven beneficial. For example, the brown trout was imported from Europe and has been widely accepted by the sport fishing community in the US. Similarly, the rainbow trout, native to the Pacific Northwest, has been widely distributed in the US and internationally. It is highly valued by both the sport fishing and aquaculture communities and as far as we know, has had little negative ecological impact.
Various biological controls for weeds or insects from foreign countries are being examined by the USDA and others. Release of some of these control agents into the US are being seriously considered by the USDA. As part of this consideration, a risk-benefit analysis is made. Questions about introductions are not easy to resolve but require careful consideration by all stakeholders. In the US, importation of aquatic animals or plants is regulated by the USFWS and the USDA. The NAA supports the USFWS and USDA in these efforts.
The National Aquaculture Association supports environmentally sustainable development and operation of aquaculture facilities. The NAA believes aquaculture has prospered and is the fastest growing sector of US agriculture because it is environmentally compatible and aquaculture products are valued by the US consumer. Each aquaculture industry sector has unique production requirements, challenges and potential to impact the environment. Each aquaculture operation must be evaluated within a site-specific and watershed specific framework. Evaluations must be based on credible information. Regulatory and voluntary efforts must be optimized to achieve cost-effective solutions. The NAA believes that if environmentally sound watershed management programs are to be developed, accurate information must be used. Aquaculturists must participate and do their part to ensure a healthy, sustainable environment.
Prepared by the National Aquaculture Association Environmental Subcommittee