Effects of Shrimp farming on
Mangroves
SWES 474/574
Pamila Ramotar, Ashlee Rhudy and Thomas Benson
Contents
•Introduction
•Impacts of shrimp farming
•Shrimp diseases
•Benefits of Aquaculture
•Mitigating effects
•Conclusions
Introduction
•
Mangrove forests support a wealth of life, from
crustaceans to people, and most importantly the
health of the planet.
•
Forests mangroves form are among the most
productive and biologically complex ecosystems on
Earth.
•
Mangroves are evergreen trees and shrubs that are
well adapted to their salty and swampy habitat.
•
They having breathing roots (pneumatophores) that
emerge from the oxygen-deficient mud to absorb
oxygen.
•
Their location combined with their low perceived
value makes mangrove forests prime targets for
shrimp farm development.
•
Mangroves provide nursery grounds for fish and
shrimp
•
One of the greatest threats to mangrove survival comes from shrimp
farming.
•
At first glance, shrimp might seem the perfect export for a poor country
in a hot climate
•
Rich countries have an insatiable appetite for it (shrimp has overtaken
tuna to become America's favorite seafood),
•
The developing world has the available land and right climate to farm it.
•
A prime location for shrimp ponds, though, happens to be the shore zone
occupied by mangroves, marshes or mainly salty flats
•
•
The relative to low ecological value of tropical and subtropical marshes
and salt flats, have been conceived as coastal wastelands with low
ecological and economic value.
•
This has led to of loss of marshes through land development or
modification for use in shrimp farming.
•
Few attempts have been made to value salt marshes in economic and
ecological terms
•
To compound matters, shrimp farmers typically abandon their ponds
after a few crop cycles (to avoid disease outbreaks and declining
productivity) and move to new sites, destroying more mangroves as they
go.
Mangrove depletion is associated with shrimp aquaculture in Asia
and Central America.
• Large areas of mangrove wetlands have been converted into
milkfish and shrimp farms and includes:
•
in the Philippines (205,523 ha) (Chua 1992)
• Indonesia (211,000 ha) (Chua 1992).
• 69,400 ha in Thailand
(Dierberg and Kiattisimkul 1996)
• 102,000 ha in Vietnam (Primavera 1998)
• 6500 ha in Bangladesh (Primavera 1998)
•
21,600 ha in Ecuador (Alvarez and others 1989)
• 11,515 ha in Honduras (Stonich 1995, De Walt and others 1996).
Impacts – General
• The siting locations for shrimp pond construction;
In extensive systems farms are located near the shore line to
take advantage of the tide to collect post larvae, large hectares
of mangroves are destroyed.
• the management and technology applied during the
operation of shrimp ponds;
•
the size or scale of the production and the surface dedicated
to it, and;
Depend on whether the farms would be extensive, semi
intensive and intensive based on the systems used it would
determine the management and technology used.
Impacts – General
• Seepage of brackish water from the culture ponds into
groundwater supplies
• The impact associated with intensive shrimp culture is the seepage of
brackish water from the culture ponds into groundwater supplies and
adjacent rice paddy fields.
• In some locations in Thailand, new shrimp pond construction occurs
behind mangrove zones where freshwater wetlands and rice-growing
areas are affected by surface and subsurface saltwater intrusion
generated by pumping groundwater to the ponds.
• This leads to social costs, such as a reduction in domestic and
agricultural water supplies, decreases in fish production, further
marginalization of coastal fishermen, and displacement of labor
• The use of groundwater has resulted in land subsidence.
Impacts – Effluents and Shrimp Pond
•
Effluents from shrimp ponds are enriched in suspended solids,
nutrients, and biochemical oxygen demand (BOD) with
concentrations largely depending on whether the management
is extensive, intensive or semi intensive
•
Studies have clearly shown that BOD, ammonia, chlorophyll a,
and total suspended solids increase with stocking density
•
extensive shrimp ponds produce few wastes, semi intensive
ponds produce intermediate waste loads.
•
the degree of intensification, i.e., higher stocking density ,use of
water, feeds and fertilizers, produces an increased waste load.
•
When effluents derived from agriculture, industry, and
municipal areas are combined, sources of good quality water
are sometimes scarce.
•
When weather and tidal conditions (i.e., cloudy days, low
winds, and neap tides) are combined, the result is a critical
degradation of water quality in the shrimp ponds and the
adjacent estuarine/lagoon waters.
Impacts – Capture of Wild Post larvae and
Wild Shrimp Stocks
• Mortality of shrimp fry bycatch, loss of
mangrove ecosystems, and genetic
degradation of native populations may
all contribute to a decline in biodiversity
.
• During the 1980s and 1990s, about 35%
of the world's mangrove forests had
vanished.
• Shrimp farming was a major cause of
this, accounting for over a third of it.
• Mangroves, through their roots, help
stabilize a coastline and capture
sediments; their removal has led to a
marked increase of erosion and less
protection against floods.
Shrimp Farming and disease
•
Its an aquaculture business used to raise
shrimp for human consumption
• World production is close to 800,000 metric
tons, about 30% from shrimp raised on farms
in more than 50 countries.
• It is estimate that farmed shrimp will account
for more than 50% of total global production
within the next five years.
• While approximately 99% of farmed shrimp
are raised in developing countries, almost all of
it is exported and consumed in rich, industrial
countries - the US, Western Europe, and Japan.
• Since 1993 shrimp farming has encountered
many issues that is believe to be viral
diseases and is the main reason for the collapse
of the industry.
Cultured Systems
There are three types of systems used to raised and culture shrimp.
•Intensive culture system: the shrimp are raised in high density and
insensitively managed tanks and ponds
•Semi-intensive system: the shrimp are raised in moderate densities
with some management in cages and ponds
•Extensive systems: Shrimp are raised in low density ponds or tanks
with little management in natural bodies of water
In Intensive and some semi–intensive systems prevention and
treatment of disease is possible, however because of the high density
of these systems it aids the development and transmission of the
diseases.
In extensive systems treatment is impractical.
Diseases
•
Shrimp are susceptible to protozoa,
fungi, bacteria, and viral diseases.
•
Antibiotics can be used to combat
protozoa, fungi and bacteria caused
diseases
•
11 different virus disease of shrimp
•
Consisting of three parvo-like, 2
reo-like, toga-like virus, and many
baculoviruses
•
The major pathogen in china is
IHHNV
(hypodermal
and
hematopoietic
necrosis
virus),
which is a parvo-like virus that
causes high mortality rates in
juvenile shrimp
This picture shows Shrimp with IHHNV disease which is
seen in the bent rostrums
• They found that there is
an
occurrence
with
affected areas and the
nutrient content of the
estuary
• Due to less rain and runoff the salinity of the
estuaries is high and in
range to grow bacteria
• Also the decrease in river
flow cause nutrients to
build up in the estuaries
causing nutrient loading.
This picture shows shrimp with the white spot virus.
Measures taken to prevent disease
• Disinfecting the farming ponds before
stocking
• Enriching nutrition in the estuaries
• Improving ecological conditions
• Improving water quality (grow in low
salinity water)
• Supplying high quality feeds to the
shrimp
• They also use polyculture
Polyculture
• The main system used is the shrimp-fish system.
• This helps because the fish eat the sick and
infected shrimp stopping disease transmission
and improving the balance in the ecology of the
pond.
• Problem: The fish may cause shrimp survival to
be low.
Capture of wild postlarvae
• Wild fry provides seed for many
shrimp farms
• Collection of wild fry can lead to
bycatch waste which hurts local
fish populations
• Can have devastating effect on
weaker ecosystems
Benefits of aquaculture
•Aquaculture is a sustainable global
seafood source
•Important economic role in developing
countries
• Provides millions of jobs worldwide
•Little to no effect on local marine
populations
Benefits Continued
•Aquaculture can reduce pressure from
commercial fishers
•Applicable to a variety of fish and crustacean
•Year round production provides room for world
population growth
Sustainable aquaculture
• Can be obtained through practices that are
environmentally no degrading,
economically viable and socially acceptable
• Proper management and regulations are
key
• Biggest inhibitor is lack of knowledge
worldwide
Mitigating the impacts - Effluent
• The polyculture of bivalve mollusks, fish, and
shrimp, using pond water to feed oysters,
mussels, and seaweed in the effluent streams
• Use of shrimp farm effluents to irrigate salt
tolerant crops. Glenn and others (1991) and
Brown and others (1999) found that various
plants in low salinities (Salicornia bigelovii,
Atrilplex, Distichlis) and high salinities
(Suaeda esteroa) remove nitrogen from shrimp
effluents effectively.
Mitigating the impacts - Shrimp pond
The alternatives for use are:
• To convert to salt ponds
• Culture of other species
(shellfish and crabs)
• To restore the ponds for
halophyte
and/or
mangrove plantings.
Mitigating the impacts
Pond Designs
• Improved pond designs (Dierberg and Kiattisimkul 1996, Sandifer
and Hopkins 1996), construction of wastewater oxidation–
sedimentation ponds,
• Reduction of water exchange rates are also examples of actions to
mitigate water quality deterioration.
• Improving the method for feed supply (Pa´ez-Osuna and others
1998)
• Improve the nutrient composition of the feed (Avnimelech 1999)
could be an effective strategy for lowering the load of nitrogen and
phosphorus released into the environment.
• Another alternative is to use mangrove wetlands as filters of pond
effluents prior to their release into adjacent waters.
Mitigating the impacts - Capture of Wild
Postlarvae and Wild Shrimp Stocks
• Regulate wild fry by catch by establishing:
1. suitable sites,
2. periods,
3. catch effort
4. stimulating the use of hatchery post
larvae.
Conclusions
• Shrimp farming has caused social dislocation, ecological
change, and environmental destruction that is arguably
worse
• Serious environmental problems include the destruction of
coastal wetlands, water pollution, disruption of
hydrological systems, introduction of exotic species, and
depletion and salinization of aquifers.
• Most critical social problems identified by local peoples is
the loss of communal resources - including mangrove areas,
estuaries, and fishing grounds - that local people depend on
for both subsistence and commercial economic activities.
Best Management practices
1. Pond preparation
2. Good quality seed selection
3. Water quality management
4. Feed management
5. Health monitoring/Biosecurity
6. Pond bottom monitoring
7. Disease management
8. Better Harvest and post-harvest
Practices
9. Record maintenance/Traceability
10. Environmental awareness and
instituted educational programs helps
to promote suitable shrimp farming
Income from pre-existing livelihood activities like fishing
and farming may be affected negatively by the loss of
habitat and environmental degradation.
Benefits related to broadening the economic base of rural
areas, generating local employment, enhancing food
security, and conserving local environments
Mangrove protection laws are enacted in many countries
New farms are usually of the semi-intensive kind, which
are best constructed outside mangrove areas
There is a trend to create
tightly controlled
environments in the farms, with the hope to achieve
better disease prevention
• Waste water treatment has attracted attention; modern
shrimp farms have effluent treatment ponds where
sediments are allowed to settle at the bottom and
other residuals are filtered.
• Low-intensity polyculture farming for some areas are
recommended
• Mangrove soils are effective in filtering waste waters
and tolerate high nitrate levels,
• The industry has also developed an interest in
mangrove reforestation
References
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Alongi, D. M., K. G. Boto, and A. I. Robertson. 1992. Nitrogen and phosphorus cycles. Pages 251–292 in A. I. Robertson
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Alvarez, A., B. Vazconez, and L. Guerrero. 1989. Multi-temporal study of mangrove, shrimp farm and salt flat areas in
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