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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
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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
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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-
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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
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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
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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.
.
. .. . . · .. ~
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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
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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.
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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-
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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
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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
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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
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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-
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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~.
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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
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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.
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Representative terms from entire chapter:
world aquaculture
