REPORT OF CONSULTATION/SEMINAR ON COASTAL FISHPOND ENGINEERING
The Consultation/Seminar started with a discussion of the environmental aspects that are important to coastal aquaculture development. It provided and noted the existence of guidelines for site selection; identified types of appropriate layouts, designs and structural details for coastal fishponds; observed methods of construction used; and noted the engineering equipment and facilities used for management, repairs and maintenance. The major recommendations include: (i) writing of a manual on coastal fishpond engineering; (ii) holding a seminar on economics of aquaculture participated in by economists, aquaculturists and engineers; (iii) conducting extensive regional and national surveys and application of recently developed methods dealing on acid sulfate soils; and (iv) regional survey of equipment and facilities for use especially for small-scale aquaculture. The report that follows details the Seminar findings together with relevant conclusions and recommendations.
In the Southeast Asian Region, the annual production1 of fish through aquaculture amounts to 686 700 tons valued at US$781.5 million. Of this, some 268 500 tons valued at US$338.5 million are produced from 393 500 ha of coastal fishponds. The potential for further development is high as it is estimated that there are some 20 million ha more in this Region of which 10 to 30 percent may be developed for this type of production. Also, existing projects are gradually increasing in their yields through intensification.
Except in few countries, the system of production in the Region is of the extensive type characterized by the use of large areas and very limited use of inputs. Examples of typical milkfish, unless specified, yields (kg/ha/year) in some countries are: Indonesia, 500; Philippines, 700; Taiwan (China), 2 000; and Thailand, traditional 190 (shrimp only) and intensive, 1 000 (shrimp only).
The coastal fishponds in the region have been of very long existence probably dating back to at least 200 years ago. Their designs, layouts and construction are crude with the first ponds formed by merely connecting natural mounds in the swamps to form the dikes and allowing stocks trapped within the enclosure to form the crop. Water control structures were not used to begin with.
The continued use of these inadequately constructed ponds has been a major setback in the proper management of the fishponds and in increasing yield therefrom. Complete losses, even during calamities of slight nature have been experienced.
Fluctuations in environmental parameters in pond culture directly and indirectly affect the performance of a culture system. In operation management planning, it is therefore essential to ensure that daily, seasonal, and longterm variations of the critical environmental parameters are predictable and manageable.
In coastal fishpond development, the most exhaustive consideration of environmental factors is necessary to ensure the manageability of culture operation and the attainment of yield targets. In particular, the characteristics of seasonal variations in environmental factors such as water quality, weather characteristics, pollution levels, and many other relevant variables should be considered.
Several site survey methodologies have been presented at the Consultation/Seminar and others pertaining to coastal aquaculture are to be found in the recent literature from, and in private developments in the Southeast Asian region.
Basically, these methodologies approach site selection as a two-stage procedure. The first state, based mostly on already existing data, provides a set of promising sites which will require further in-depth and field investigation before a final site selection can be made. The second phase consists of the in-depth and field investigation as well as the final site selection process.
The state of the art in site selection for coastal pond culture appears to be adequate. Based on the perception that comprehensive site selection information was not readily available throughout the region, the Consultation/Seminar participants recommend the preparation of a manual on coastal aquaculture site selection, which would lay out existing procedures, criteria, sampling methodologies, and interpretation of results, including ranking and scoring.
Proper site selection is recognized as the first step toward guaranteeing the eventual success of a coastal aquaculture project. The other elements, which build on proper site selection, are design, layout and management. Basic criteria for site selection are well known. However, a recurring problem, one emphasized at the Consultation/Seminar is the need to objectively determine the relative weight of each criterion. To achieve this, a scoring system is helpful in making the final site selection. It was however, pointed out that the weight (i.e., relative importance) of each selected parameter will vary according to the overall objectives in each case (e.g., social welfare versus economic gain). It will also vary according to the biological characteristics of the organism to be cultured (e.g., one requiring high water quality versus the other being relatively tolerant to low water quality conditions, as well as in terms of other purely economic factors such as availability of markets, and market price of the product). The latter is further complicated by differing supply/ demand situations in different parts of a country.
The Consultation/Seminar has recommended that this problem be studied in-depth as a part of the preparation of the site selection manual.
Under certain circumstances, the location of a new fishpond can have a considerable impact on the environment. In other cases, it may be quite beneficial (e.g., enhancing the value of the local environment, and thereby making it too expensive for destructive uses to be undertaken). Other impacts may be negative, such as the removal of mangroves which are important for maintaining proper balance of the ecosystem and of capture fishery resources. Guidelines are available for minimizing the negative environmental impacts of coastal aquaculture in mangroves. However, a problem is that these guidelines are not sufficiently detailed to be of use to aquaculture planners and coastal aquaculture engineers; and therefore, it has been recommended that steps be taken to frame these guidelines, especially with reference to the provision of a green belt (so that they can be practically applied).
Acid sulfate soil covers more than 5 million hectares of the low lying coastal tidal plains in Southeast Asia. With careful planning, this idle marginal area offers some possibilities for the expansion/development of brackishwater culture industry to produce more food without endangering the balance of the ecosystem. The main problem lies on the fact that extreme acidity will arise in the ponds built on such soils.
Through experiments conducted recently, a simple, cheap and rapid method of reclamation has been developed to remedy the acidity. The method consists of a repeated sequence of drying, filling, submergence and flushing with seawater of the pond bottom and leaching of relatively big dikes. Through this reclamation method, acidic soils could be made productive within a relatively short period of a few months. As this problem is of great importance to the further development of this industry, as well as in improving the yields of existing fishponds, countries concerned are urged to conduct surveys and spread the use of the method to establish the feasibility and potential of its widespread application.
Coastal fishpond development schemes should have proper layout design superimposed upon the site available. This should consider minimum disturbance to the balance of the ecosystem, the requirements of the species to be cultured, and the management practices to be adopted.
In environmental considerations of the layout of coastal fishponds, the preservation of the technically advisable (based on thorough study) coastal and riverine mangrove buffer zone (green belt) should be strictly followed. In some instances, this conserved strip should even be enlarged to provide adequate exit of floodwaters during the peak wet season in the year. In addition, especially for large developments such as those over 50 hectares, lines or patches of mangrove vegetation may be retained to advantage within coastal fishpond development sites. Environmental impact studies, with the proposed layout of project, should be required before the release of areas for coastal fishpond development.
The layout should provide the different types of ponds needed, properly located water control structures and a system of water supply canals for each of water management within the system.
A complete coastal fishfarm will need nursery and grow-out ponds, and in some instances transition ponds for holding intermediate size fish. These types of ponds are properly proportioned and positioned within a fishfarm.
The gates should be located where they are not exposed to strong weather forces and where water of good quality can be allowed to enter the fishpond system. Proper location of the gates can also serve to aerate the pond water and to promote water circulation.
The water supply canal and the system of main, secondary and tertiary gates will provide the facilities for water management and should be properly placed and constructed.
For milkfish monoculture and for milkfish/shrimp polyculture, the layout consisting of nursery, transition and rearing pond plus system of gates and canals will be adequate. Modification would occur if the requirement is for nursery alone, or for grow-out only. In the case of shrimp monoculture, only small nursery compartments which may even be temporary, and rearing ponds are required. It is preferable to have separate water inlets and exit gates for each rearing pond to provide better circulation and aeration. For shrimp ponds aeration over the pond bed is especially essential.
Modifications in fishfarm layout to provide for intensive management will be required. For milkfish monoculture and milkfish/shrimp polyculture, the multiple stock/ harvest type (stock manipulation type) was developed in Taiwan and is being tested in the Philippines. Another modification initiated, the modular type developed in the Philippines, is fast gaining popularity. In Thailand, a rapid change is being made in the layout of ponds from the conventional type to the semi-intensive and intensive layouts as the needed inputs become available (mainly seeds and feeds).
The design of dikes depends predominantly on soil characteristics. The side slopes of dikes are designed for structural stability, the ratio of horizontal length to height ranges from 1:1 to 3:1. The height and width of dikes depend on the types of dike such as primary, secondary or tertiary dikes. These are also governed by the tidal conditions, flood level, pond water depth, soil shrinkage and freeboard. Permeability of the soil must be considered while designing the dike.
The proper combination and fitting of water control structures with the existing tidal range and pond area, are the key to success in the efficient water management of the fishfarms. Smooth operation in attaining the required amount and exchange of water are dictated largely by control gates from the source to the remote ponds of the farms. It is important that these water control structures should be adequate for efficient pond management. These are more lasting if made of concrete but wood is also used.
Water conveyance structures (canals, channels) provide the needs of management, as supplying new water into the ponds and draining out the old water. They also provide the facility for holding and harvesting of fish and of serving as a waterway for the relay of farm supplies. It is necessary that this component of a fishfarm is adequately provided and structured.
It is considered that a fishfarm is properly planned if all the water control structures, canals and the different pond compartments mutually complement each other. This complementary function can vary with management used and species cultured. The fishpond system should be planned and constructed to suit the particular situation intended.
There is a wide range of methods used for coastal fishpond construction in the region. This varies from simple manual construction to the use of heavy machinery. The equipment to improve the efficiency of manual construction have been identified. In mechanized method, the dragline has so far been the only suitable equipment for dike and coastal pond construction. There is the need for other types of mechanized construction equipment that are more versatile and suitable for varied fishpond site situations and also for building small-scale projects.
Clearing the area of vegetation is done in several stages, including the activities of underbrushing, cutting and felling of trees, destumping, stripping and disposal. The chainsaw, winch, dozers and draglines were mentioned in addition to manual tools used for clearing.
Maintenance and repair works in existing fishponds are essential to the success of pond culture performance. Indigenous tools have been identified as useful for these purposes in the different countries in the region. Identification and selection of the more efficient implements now in use are necessary so that their wider use in the region can be promoted. It is also noted that materials and equipment used require maintenance. The use of preservatives and protective materials, (e.g., paint, grease, etc.) is necessary.
Resulting from the long history of coastal fishponds in the region, standard equipment for management and operations have been developed. It has been noted that some of these equipment, from the technical or engineering point of view, are not necessarily efficient and can be improved. Also, many of these are borrowed or developed for other uses such as in agriculture. Fabrication of equipment most suitable for fishpond management and operation will be needed.
There is a large storage of information on the use of wind, solar power and other labour-saving and motion-economizing implements and facilities. These would be particularly useful in improving the efficiency of operations of small-scale aquaculture ventures. However, this information is scattered in many countries and among many specialized agencies. It is recommended that a thorough study be made on the collection, compilation and dissemination of this information. This activity should especially identify the appropriate technology which can be applied for the coastal aquaculture industry and part of the collection process could perhaps be accomplished by accessing computerized bibliographies on this technology.
The present cost of designing and constructing coastal fishponds is relatively high varying from country to country and ranging from US$2 000 to US$10 000 per hectare. The recovery of this investment varies from 3 to 10 years.
Profitability contributes to the farmers' welfare. Profitability also serves as a reference for the financing agency to determine to what extent the farm can be expanded.
Adequate definition of design requirements are necessary for the aquaculturists based on their parameters. The standard and quality of finished construction works should be made known. The need for incorporating construction method in fishfarming with the use of suitable and available equipment should be considered. Work flow system should also be devised to operate the farm.
It has not been possible to arrive at a comprehensive indicative costs of coastal fishpond design, construction and maintenance in view of the diverse variety of circumstances and culture management systems currently under practice in the region. Similar difficulty is experienced in the estimation of the recovery of investment costs. This is further complicated by the absence of representative statistical information.
The assessment of operational costs and the level of annual profit is similarly handicapped. In an attempt to illustrate the operation and capital costs for a number of the common systems of culture for both crustaceans and finfishes, rough cost estimates for a number of known farms have been compiled only to provide some general indications for the purpose of discussion.
It is realized in this Consultation/Seminar that there is very little known about the economics of the aquaculture industry including that of the engineering aspects. That this knowledge would be very useful for the further development of the industry needs no further argument. There is the need for a well-concerted study in this subject especially on a multi-disciplinary basis. It is recommended therefore, that a follow-up Consultation Seminar on the economics of coastal aquaculture be conducted at an appropriate time in the near future to be participated in by economists, aquaculturists, engineers and marketing specialists of fish and fishery products.
On financial assistance to the small operators, the group considers there is considerable room for improvement especially with respect to the timeliness in the issuance of loan and the need to raise the ceiling of credit facilities. In many cases, the size of a loan is difficult to defray the development or engineering cost of a small-scale farm. Since the cost per unit area is considerably less in large-scale development, it would appear prudent to collectively develop small-scale farms on a cost-sharing basis. In countries where farm development emphasizes the use of the manual method, the problem of defraying the development cost would not appear to be as pressing.
In considering the present constraints in the development of coastal fishponds, a number of dependent and independent variables have been identified. While acid sulfate soils present the greatest obstacle, the absence of standard and/or recommended methods for site selection, the lack of assurance of maintaining acceptable environmental conditions, and the expected conflict of interest with common users of water and land resources are particularly noteworthy.
Based on the recognized needs of coastal aquaculture development, a programme of work on coastal aquaculture engineering is proposed to facilitate that development.
Development of expertise and skilled labour. This can be achieved through appropriate training programmes at national and/or regional levels.
Development of suitable equipment. The diverse nature of developable areas would necessitate the engagement of varying types of equipment.
Programmes for education, training and technical extension. There is a true need to develop professional resources at all levels in coastal fishpond engineering through suitable education and training arrangements deemed necessary by each country. In this consideration, emphasis should be given to the development of functional extension personnel. To facilitate these undertakings, the Consultation/Seminar recommends the compilation of a “Manual for Coastal Fishpond Engineering”.
Research and development programmes. To facilitate and to accelerate these and other developments, the need for reliable information should be satisfied through appropriately integrated research and development programmes.
