Aquaculture is considered
to be the fastest growing area of U.S. agriculture. The positive impacts
of aquaculture are well documented. For instance, proponents of aquaculture
argue that aquaculture reduces the worldís dependence on wild stocks
of fish, provides new jobs, and helps to feed the worldís growing
population (http://www.csmonitor.com/durable/1998/09/09/fp1s4-csm.shtml
9/21/98). However, aquaculture, commonly presented as being a clean
industry, also produces some negative environmental impacts.
Many of the aquaculture
farms operate without a negative impact on the environment. In fact,
catfish, tilapia, and freshwater carp can convert harmful organic wastes
into edible fish meat. However, the farming of shrimp and salmon has
been found to have a negative impact on the environment. For example,
when the cages are crowded, uneaten feed, fish wastes and antibiotics are
released from the cages. As a source of nutrient pollution, these
wastes create high levels of nutrients that increase the growth of phytoplankton
and algae. The eventual degradation of algae drastically reduces the
levels of oxygen in the water, which will kill fish or other organisms.
Subsequently, wild fish suffer from poor water quality, the loss of bottom
habitat, and the outbreaks of disease. In addition, the shrimp and
salmon need to be fed other fish, such as sardines and mackerel, for survival.
Growing a pond of salmon may require three to five pounds of wild fish.
As a result, shrimp and salmon consume more protein than they produce.
If the growing of fish produces a net loss of protein, then aquaculture
creates a negative ecological impact. When fish is removed from wild
food webs, ìless food may be available for commercially valuable
predatory fish and other marine predatorsÖî (http://www.edf.org/pubs/Reports/Aquaculture
10/4/98). Critics of aquaculture, such as Rebecca Goldburg of the
Environmental Defense Fund, remark that ì ëby taking these fish
out of the ocean to feed to farmed fish, weíre undermining the integrity
of the marine food webíî (http://www.csmonitor.com/durable/1998/09/09/fp1s4-csm.shtml
9/21/98).
Overcrowding appears
to be the major cause of environmental problems when salmon and shrimp are
being raised. The aquaculture industry is currently attempting to
correct the problem by working on ìplant-based feed products and
improved husbandry practices that reduce the risk of disease and pollutionî
(http://www.csmonitor.com/durable/1998/09/09/fp1s4-csm.shtml 9/21/98).
The use of a closed-loop system has also been proposed as a possible solution
to the problem. The systems used to raise salmon and shrimp, namely, cage
and netpen systems, are the most likely to discharge untreated waste.
A closed-loop system would allow farmers to monitor and tract polluted water
before itís released into wild fish populations.
Two specific instances
of the waste discharge problem are found in Idaho and British Columbia.
Trout farmers in Idaho must reduce the phosphorous levels found in their
wastes because the Snake River is being polluted. Discharge from untreated
salmon farm waste in British Columbia has been estimated to equal the amount
of raw human sewage from a city of 500,000 people. The untreated waste
has filtered into the waters off the coast of British Columbia.
The one area of
aquaculture production that produces minimal nutrient pollution is mollusk
farming. Because oysters, clams, scallops, and mussels consume the
existing phytoplankton, mollusk farmers donít need to use fish feed.
As noted earlier, the release of untreated fish feed wastes can lead to
the reduction of oxygen levels in the water. The production of mussels
will always result in a reduction of nutrients in the water because the
filtering activity of mussels keeps the water clean (http://www.ecology.su.se/cinetpubwwwrootecology/www/stagg/max.htm
9/19/98).
Environmentalists
are also concerned with the installation of sound devices by salmon aquaculture
farmers and the killing of wild predators. Sound devices are intended
to eliminate seals from intruding into the farming area, but they are also
scaring humpback whales feeding in the area (http://www.csmonitor.com/durable/1998/09/09/fp1s4-csm.shtml
9/21/98). Meanwhile, to control bird and mammal predation, some aquaculturists
have resorted to killing the wild animals. However, frequent predators,
such as the double-crested cormorant and the seal, are protected under the
Marine Mammal Protection Act. With a lack of statistical information
on the effects of predation on aquaculture production, the killing of predators
may be just as unnecessary and unjustified as the use of sound devices (http://www.edf.org/pubs/Reports/Aquaculture
10/4/98).
Blue Tilapia
http://www.edf.org/pubs/Reports/Aquaculture
Biological pollution
is another environmental problem related to aquaculture because ecosystems
are being altered and biodiversity is being reduced. For instance,
aquaculture can be the cause of the introduction of non-native species from
one area to another. The blue tilapia that escaped from aquaculture
facilities in Florida have lead to the loss of food, native habitat, and
spawning areas for native species in Everglades National Park. In
extreme cases, an abundance of blue tilapia has lead to the loss of native
fish species and vegetation. To reduce the biological pollution problem
some aquaculturists suggest raising native species or non-native species
that have exhibited they cannot survive in the native environment.
Minimizing the release of non-native species into the natural environment
could be achieved by growing fish in secure closed systems (http://www.edf.org/pubs/Reports/Aquaculture
10/4/98).
As an important
aspect in the worldís fishery system, the aquaculture industry must
continue to work to ensure the negative environmental impacts of aquaculture
do not ìnegate the potential economic and nutritional benefitsî
(http://www.cdc.gov/ncidod/EID/vol3no4/garrett.htm 9/21/98). The challenge
for aquaculture is to develop a system that uses resources efficiently,
minimizes the release of untreated wastes, and enhances the biodiversity
of the surrounding area. Once this challenge is met, aquaculture will
truly be a responsible, sustainable industry.
Folke, Carl et al. ìEcological engineering
for increased production and environmental
improvement in open
sea aquaculture.î [http://www.ecology.su.se/cinetpubwwwroot
ecology/www/staff/max.htm].
19 Sept 1998.
Garrett, Spencer E. et. al. ìPublic,
Animal, and Environmental Health Implications of
Aquaculture.î [http://www.cdc.gov/ncidod/EID/vol3no4/garrett.htm].
21 Sept. 1998.
Goldburg, Rebecca and Tracy Triplett. ìMurky
Waters: Environmental Effects of
Aquaculture in the
United States.î [http://www.edf.org/Reports/Aquaculture].
4 Oct. 1998.
Woodard, Colin. ìFish Farms Get Fried
For Fouling.î [http://www.csmonitor.com/
Durable/1998/09/09/fpls4-csm.html].
21 Sept. 1998.
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