Mangrove + Aquaculture: a framework for a sustainable shoreline
research + goals | mangrove | aquaculture | community programs |

 

background:  

Aquaculture has a tradition of about 4,000 years. It began in China, possibly due to the desires of an emperor to have a constant supply of fish. It may have also stemmed from ancient practices for trapping fish. The husbandry of fish is not a new phenomenon. Ancient practices based on the modifications of natural bodies of water or wetlands to entrap young fish in enclosures until harvest, have just evolved into more systematic and scientific methods and techniques.  

The recent great interest In aquaculture, or the breeding and rearing of aquatic plants and animals in enclosures/confinements, was spurred by the oil crisis of the early seventies that made the exploitation of aquatic resources through fish capture highly uneconomical and due to declining fish catches in major traditional fishing grounds in a number of developing countries in the world. The farming of fish was seen as the best option to catching fish to feed the growing masses, provide them with alternative livelihood opportunities for their socio-economic upliftment, as well as generate much-needed foreign exchange to service foreign debt.

In many countries, especially in the developing world, fish and other aquaculture products serve as the main source of cheap protein to combat malnutrition and under-nutrition, fish having essential amino acids that are often lacking in cereal protein substitutes. Value-wise, cultured fish products compete with poultry and livestock in the local market. Nutrition - wise, however, aquaculture species are more efficient in converting food into body tissue than poultry or livestock (Liao, 1988).

In Asia, aquaculture products are essential in improving the largely high-carbohydrate, low-protein diet predominant in the region, where paradoxically enough, a great number of people, especially in the rural areas, engage in labour-intensive work but subsist on low-protein diets (Liao, 1988). A relatively small amount of fish protein in combination with a cereal-based diet would enhance the nutritional quality of the cereal protein, improve the overall quality of the diet, and therefore increase labour efficiency.

Baluyut, Elvira A., AQUACULTURE SYSTEMS AND PRACTICES: A SELECTED REVIEW. United Nations Development Programme. Rome, 1989

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major impacts:
+ mangrove habitat destruction
+ coastal erosion
+ sedimentation
+ flooding

pond types:

+ freshwater – fish ponds, pens, cages, rice paddies

+ brackishwater – fish ponds in coastal areas

+ marine – fish cages, substrates for mollusks and seaweeds


culture methods:
+ extensive – low stocking densities, no supplemental feeding, water change affected through tidal means, ponds are large (more than 5 ac), shallow, production low

+ semi-intensive/intensive – higher densities, supplementary feeding, use high densities of culture organism, dependent on artificial feeds, small ponds up to one ha, water managed with pumps and aerators, feeding done at regular intervals, more labor-intensive, costlier to set up and operate, production is higher

 

+ The aquaculture of Banda Aceh is primarily through the brackishwater method to produce milkfish and penaeid shrimps.

 

site selection –

+ soil quality: clay-loam, or sandy-clay for water retention and suitability for diking.

+ land elevation and tidal characteristics: average elevation that can be watered by ordinary high tides and drained by ordinary low tides; tidal fluctuation moderate at 2-3 m.

+ vegetation: area without big tree stumps and thick vegetation; areas near river banks and coastal shores exposed to waves require a buffer zone of mangrove. (The presence of Avicennia indicates productive soil)

+ water supply and quality: steady supply of both fresh and brackish water

+ accessibility: land/water transport, close to sources of inputs such as fry, feeds, fertilizers, and markets, fish ports, processing plants, and ice plants.

+ availability of manpower

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pond layout –

This depends on the species for culture and on the size and shape of the area, which in turn determines the number and sizes of ponds and the position of water canals and gates. A complete fish farm has nursery and grow-out ponds and, in some instances, transition ponds for intermediate-sized fish/shrimp. Farms can also be very small operations and run by the owner.


components –

+ pond compartments enclosed by dikes

+ canals for supply and drainage of water to and from the pond compartments

+ gates or water control structures to regulate entry and exit of water into and from the pond compartments.

 

Pond compartments are usually rectangular in shape. In Indonesia, they can be triangular, raceway-shaped, or oval. They can range from less than a hectare to several hectares each and can be operated by the owner in a backyard or at an industrial scale. The pond system is enclosed by a perimeter dike and the individual pond compartments are separated from each other by partition dikes. The perimeter dike is wider and higher than the partition dikes for protection. Side slopes of the dikes range from 1:1 to 1:3, they can be made out of soil or concrete.

 

Canals supply new water into the pond and drain out old water. They also provide access for the transport of farm supplies. Traditional milkfish ponds usually have only one canal, shrimp ponds have separate supply and drainage canals. The width of the canal depends on the amount of water they must carry.

 

Gates regulate the entry and exit of water into the ponds through the canals. Main gates regulate the exchange of water between the pond and tidal stream or sea and may be made of concrete or wood. Secondary gate regulate the water exchange between the ponds and the canals. Pipes or culverts can be used for smaller ponds.

 

maintenance –

+ Fertilization – using chicken, cow, or pig manure or inorganic materials like urea, ammonium, phosphate to maintain plankton population. Semi-intensive/intensive systems do not require fertilization.

+ Liming – maintains water pH at alkaline levels.

+ Pest Control – pesticides applied into ponds. Crabs are caught with traps. Gates should be screened to prevent entry of unwanted fish.

+ Stock Monitoring – regularly sampled for length-weight measurements to determine biomass in the pond.

+ Upkeep – pond dike and gate are checked regularly, dikes are planted with grass or vegetative cover to prevent erosion.


harvesting –

Marketable fish/shrimp are collected at the end of the culture period by draining the pond and using harvesting nets. There is no freshwater source, so the best time for shrimp culture is during the rainy season. In the dry season seawater salinity (that can reach above 45 ppm) reduces pond productivity. Farmers obtain water for their ponds by pumping seawater at high tide through the drainage dikes originally constructed for rice paddy cultivation. The same dike also serves for shrimp pond wastewater discharge. Most of the shrimp farms do not have settling or treatment ponds.

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sustainable methods -

+ Empang parit is the traditional application of integrated aquaculture in the mangrove area. It usually consists of an unexcavated central platform that alternates between being flooded and exposed and a canal that runs along the pond dikes where fish, shrimp, and crabs are cultured. Tides are used to carry seed stock into the system and to exchange water. The forests are locally run and operated and self-managed by the community.

 

+2 silvofishery models for mangrove-integrated design practice:

a. mangroves within the pond with a ratio of 60-80% mangroves and 20-40% pond canal.
b. mangroves outside the pond-similar ratio

c. mudcrab and shrimp pond system

 

Size - one hectare to thousands of hectares
Tree Density - 0.17 to 2.5 trees/m 2
  The density influences the quantity of litter production and organic load, which in turn influences the diversity of the bio-system
  Less density may be desired for species such as milkfish, but shrimp and crab prefer the shelter provided by mangroves.
Production - Only about 10% is that of semi-intensive culture
  The culture system used at the farms is mainly polyculture while monoculture is practiced in 24-32% of the farms. The cultured species include milkfish, shrimp, and mudcrab.
  Farmers earn an average gross income of US $589/ha/year. The individual farmers operate between 4 to 25 ac of silvofisheries ponds.
  Mangroves will provide only limited nutrient inputs into the system until they have devloped enough biomass.
  Increased production is added
 

+disadvantages of Empang Parit:

greater construction cost per unit area
greater difficulty to manage
reduced water circulation and greater potential for stagenent areas with low oxygen levels
limitation on species cultured
mangrove trees reduce the penetration of sunlight to ponds lowering the productivity of phytoplankton and benthic algae
potential toxicity of tannin from mangroves
in areas of Forestry Service supervised land, pond operators resist efforts to replant mangrove, as the status of the trees would revert to the Forestry Service—an outcome that shrimp farmers find unacceptable.
 
+ an appropriate silvofishery model is site-dependent. It should be integrated into an area-wide integrated approach to coastal zone management.
 

Action

Desired impact

Inform and educate shrimp farmers, local government, and the community

Increased shrimp farmer and community knowledge and understanding of the importance of coastal resource conservation to their own well being

Formation of community self-reliance group and mangrove Committee

Increase participation, awareness, and community empowerment to influence resource use decisions, and ability for self management.

Training on integrated coastal management for government staff, community members, and shrimp farmers

Increase understanding of integrated coastal resource management processes and methods.

Partner with and train local NGOs

Increase local capacity for coastal resource management and sustainable shrimp culture practice

Demonstration pond

To establish a learning facility to experiment with and promote small and incremental changes to traditional practices that are more sustainable. By offering a successful example it is the expectation that this will build trust among shrimp farmers and willingness to adopt new practices.

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resources:
Integrated Mangrove Forest and Aquaculture Systems - Indonesia - http://www.mangroveweb.net/html/aqua.htm
Aquaculture Methods and Practice: A Selected Review - http://www.fao.org/docrep/T8598E/t8598e05.htm#4.3.2%20site%20selection
Good Practices for Community-based Planning and Management of Shrimp Aquaculture in Sumatra, Indonesia- a pilot project in Pematang Pasir, a coastal village located in Lampung Province on the island of Sumatra, http://www.crc.uri.edu/download/Good_Practices_Aquaculture-Sumatra.pdf