by
U.W. Schmidt
Fishery Officer
Aquaculture Development and
Coordination Programme
FAO, Rome
The paper outlines briefly the potential role of coastal aquaculture in integrated rural development and emphasizes the relevance of socio-economic aspects for adequate planning and implementation. As a first step of planning it suggests a comprehensive study of the socio-economic and socio-cultural determinants of the rural society for which the introduction of coastal aquaculture is considered. This analysis is expected to examine the structural deficiencies of the social system and to identify the actual needs of the target population groups for which the development of aquaculture appears viable. Concluding from the findings of the socio-economic analysis, the paper suggests to formulate a social postulate which, followed throughout planning and implementation, would ensure the development effort to yield a significantly positive socio-economic impact.
The process of studying a socio-economy and formulating the social postulate is outlined using a case study undertaken by the author in Kenya.
Additionally, the importance of a legal framework and of marketing is emphasized, using as an example the shrimp culture industry in Ecuador.
The last part of the paper discusses the process of implementing coastal aquaculture and proposes the active and responsible involvement of the people as one of the decisive factors for its success. Additionally, it stresses the relevance of vertical and horizontal integration for coastal aquaculture.
Aquaculture, the raising of aquatic organisms in a controlled environment, is a relatively new technology in tropical Africa. Freshwater fish culture has been practised for a considerable time in some African countries and has yielded good, sometimes spectacular, results. Coastal aquaculture, however, has to be considered in, its very early stage of development in the continent. Coastal areas suitable for aquaculture are believed to exist in abundance and a rising interest among policy-makers and economic planners in exploiting these resources has been observed.
In the course of rural development, coastal aquaculture can offer attractive possibilities to improve the structure of the rural socio-economy:
rational exploitation of existing resources;
production of valuable animal proteins for human consumption;
creation of income and employment;
diversification of primary production;
substitution of imports, and
increase of foreign exchange earnings through export of high value products.
The achievement of all or some of the above objectives will depend - apart from the material or technical requirements - largely on the way in which coastal aquaculture is planned and implemented. If, for example, the main emphasis of the national development plan is placed on the creation of employment and food for people from the existing resources, a low-cost input, labour-intensive method of production should be chosen; if generation of foreign exchange is of greater importance, high-value species suitable for export should be cultured.
Aquaculture production, unlike capture fisheries, can be planned similar to agricultural production, because of the direct relation between inputs and outputs. Although there will always be a number of variables which cannot be fully determined in advance (input-cost variations, demand variations, etc.), a technical and economic feasibility study can usually extrapolate expected outputs and cost-benefits with a reasonable degree of accuracy.
The appraisal of the technical and financial viability of technological change has been verified in the case of many such projects, whereas the social and economic benefits envisaged to be generated often fall short of the expected. Repeated and costly failure with respect to the positive and measurable socio-economic impact of a promising technical innovation has revealed, in recent years, the relevance of socio-economic factors and their consideration in the planning and implementation of development projects. In analysing the negative experience, governments and international agencies have come to the conclusion that an approach to development which limits itself to technical and financial considerations will possibly stimulate increased production; whether this will bring forward a positive change in living conditions of the people involved remains problematical. Consequently, a reorientation of development concepts has taken place during the last few years. The limited and technocratic strategy to increase production by providing material inputs and technical assistance has been expanded to include non-techno-economic considerations. After years of concentrating on the improvement of the input-output ratio of production, a concept wherein the producer was merely one of the production factors, the feasibility of a proposed technical innovation is now also judged by its anticipated impact on the standard of living within the rural population. The small farmer, the landless labourer, and the artisanal fisherman, have become the ‘object’ of development. The consideration of technical and economic feasibility of a development effort is now often being supplemented by anticipating its social impact.
The described re-oriented approach to development requires, consequently, a new approach to project planning and implementation. In this paper we shall examine and discuss the aspects, variables, and parameters usually subsummed under the term ‘socio-economic’. As presently used, socio-economic aspects comprise the complexity of non-technical and non-economical1 considerations which are decisive in the process of project planning, implementation, and evaluation. To make this complex operational, we will divide it into categories of social, economic and cultural aspects, and variables, always keeping in mind that only the realization of their interdependence and interaction allows a comprehensive analysis. Additionally, it should be mentioned that the scope of this paper allows us only to point out and discuss selected aspects and variables of each category; the actual analysis may consider additional aspects specific to the socio-economic entity which is to be examined.
The general hypothesis which this paper attempts to verify can be formulated as follows:
the innovation of a technology in an existing socio-economic reality will result in social change, and
the character of this change will be determined by the value given to socio-economic factors during the innovative process.
An approach to project planning oriented toward improving the living conditions of the people affected will result in a design of the expected technological changes to achieve the postulated socio-economic results. It will alter the technology to be appropriate, to ‘fit’ the reality according to the existing resources and needs of the individuals and social entities involved.
At this initial stage of planning two dimensions are, therefore, to be taken into consideration:
the socio-economic reality, and
the social postulate.
Together with the appraisal of the technical and financial viability of a project which proposes the development of coastal aquaculture, a comprehensive study of the socio-economic dynamics of the rural society should be undertaken. Only knowledge of the present social, economic and cultural organization of the community which is going to be affected by the project will provide a reflection of its possible impact. In the following paragraphs we will discuss some of the variables which interact in most rural societies and which will determine whether coastal aquaculture can be successfully integrated into a social system and its economic base.
2.1.1 Demographic and economic parameters
2.1.1.1 Demography. The evaluation and interpretation of demographic data will result in an understanding of the population structure. Relevant demographic data to be compiled usually comprise:
2.1.1.2 Infrastructure. An evaluation of the infrastructure of an area will identify the constraints to development. The aspects to be investigated are:
2.1.1.3 Sector analysis of the local economy. The analysis will investigate the different sectors of an economy, usually dividing it into: (a) a primary sector as agriculture, fisheries, forestry, mining, etc.; (b) a secondary sector as industry and manufacture, and (c) a tertiary sector as services, trade, tourism, etc.
For each sector, the analysis will briefly examine the following:
2.1.1.4 Income distribution. The distribution of income in the different strata of a society will identify underprivileged population groups and allow, by estimating the purchasing power within different strata, the extrapolation of the domestic market potential. For each occupational group, relevant to the development effort, the following data should be collected:
2.1.1.5 Expenditures and consumption patterns. The household expenditure pattern of the different strata of a society provides information about the general standard of living and the nutritional status. Household expenditure and consumption habits can be analysed if the following data are compiled and cross-referenced for different income groups:
If the above-listed data have been compiled and interpreted, we dispose of most of the principal parameters which determine the economic basis of a society at a given moment. We have, so to speak, a static image of the society. Having analysed the data and parameters we can, in many cases, anticipate existing structural deficiencies. To achieve an understanding of the dynamics of the society, we shall examine the social factors which may explain some of the structural deficiencies reflected in the economic data.
2.1.2 Social dynamics and variables
To understand the interaction of individuals and groups in a social system, the factors which determine its functioning (or non-functioning) must be identified. These factors will vary in significance from case to case but, in general, we can assume the following to play an important role:
In addition to the above variables, other factors will have to be examined in most of the specific studies depending on the special conditions of the social system in question. Whereas the initially-discussed demographic and economic parameters can normally be quantified, the variables which determine a social system require a qualifying analysis and are often better expressed in narrative form. The same methodology will have to be used in discussing the aspects which belong to our third category.
1 In the sense of how the individual can change from one organization to the other
2.1.3 Socio-cultural aspects and considerations
Having studied the economic base and the organizations of a social system, and in order to complete our evaluation of the socio-economic reality, we shall examine a selection of socio-cultural variables which explain the role and status of individuals and nucleus groups such as families, clans, etc., and their motivational structure and limitations. Such variables are, for example:
From the analysis of these and other socio-cultural characteristics of a social entity, we can approximate the innovative potential of the individual, as well as group attitudes toward change. We can identify culturally motivated constraints and predict, to a certain extent, how the individual will react to technological change and its social implications. From the evaluation of the socio-economic reality which we have however roughly attempted to outline, we can now formulate the social postulate.
Most nations of the African region can be sociologically defined as transitive societies, and many areas suffer from structural underdevelopment. The identification of the nature and magnitude of such deficient structures was, apart from analysing the major determinants of a social system, the purpose of the previous section. To formulate a social postulate, which reflects existing deficiencies and at the same time takes into account the technical and economic feasibility of coastal aquaculture development projects, we have to run three criteria against each other:
the technical and economic parameters which determine the feasibility of coastal aquaculture;
the actual needs of the people and/or the requirements for a structural improvement of their community, and
the potential impact of the innovation of coastal aquaculture with respect to those needs and requirements.
As the three criteria consist of many variables, it would be inadequate to demonstrate their interaction using a simplified model. We shall, therefore, leave the level of abstraction which was useful for the general analysis of a socio-economic system and use a case study to discuss the potential role of coastal aquaculture in rural development and the relevance of economic, social, and cultural factors for the planning of such a development.
Many parts of the east coast of Africa are potentially suitable for coastal aquaculture. In 1977, a mission of the interregional Aquaculture Development and Coordination Programme of the Food and Agriculture Organization of the United Nations selected the Malindi area in Kenya for the establishment of a pilot project to demonstrate the feasibility of coastal aquaculture. A preparatory phase was started in 1978 and, after finding the techno-biological conditions satisfactory, construction of the pilot farm commenced in May 1979. The author visited Malindi in May/June 1978 to study the socio-economy of the area and provide recommendations for a strategy to replicate coastal fish farming along Kenya's coast. Following the order of the three criteria established in the previous section, we will now, for the Malindi sub-district, discuss the different variables and their implication for a social postulate.
2.3.1 Technical and economic parameters
For the Malindi project the culture of mullets, siganids and shrimps was recommended because of:
The expected production of a 50-ha coastal aquaculture venture would, if appropriately timed, be 1 200 kg of finfish and 500–600 kg of shrimp per week, having a value of about US$ 2 000. The gross annual income would thus be about US$ 106 000 per year. The major factors on the cost side would be stocking material, feeds and fertilizers, labour and the depreciation of the costs of construction plus interest. Stocking material (fry and juveniles of the proposed species) can be caught in the coastal waters and require only labour and equipment (boats, nets, etc.). The same applies to farm construction, which is done by manual labour. Feed and fertilizers (maize bran, trash fish, slaughterhouse wastes and livestock manure) can be acquired locally. The availability and costs of the different inputs are presently being investigated by the pilot project; therefore, a detailed financial cost benefit analysis would be premature at this writing. However, in addition to the predicted technical and biological feasibility, the present estimates with respect to the commercial viability of coastal aquaculture in the Malindi area indicate the probability of high profit margins. The technical and financial feasibility has to be considered the conditio sine qua non of coastal aquaculture development, and having confirmed it as highly probable, the next step was to study the local socio-economy and identify structural deficiencies.
2.3.2 Requirement to improve the standard of living of the population
To identify the needs of underprivileged population groups in the sub-district, some of the relevant results of the study pointing out structural deficiencies will be briefly examined in the following (using the methodology discussed in 2.1).
2.3.2.1 Demographic parameters. Due to the unavailability of recent population figures, the present population had to be estimated, using the results of the last census and approximate growth rates (urban 7 percent/annum, rural 3.1 percent/annum). According to the calculation, the present population of the sub-district is almost 140 000, of which about 13 percent live in urban areas. The average density is 24 persons/km2 with a significant (up to 600 persons/km2) concentration close to the coast. Sixty-five percent of the people are of local African origin (Mijikenda), 30 percent are Bajuni or Swahili people (northern tribes who have frequently intermarried with Arab immigrants and have immigrated south during the last centuries). Five percent are Asian and European. The female/male ratio is about 52:48. Because of the high degree of subsistence production, the economically active population could not be assessed, but unemployment and underemployment is evident, especially among the rural population.
2.3.2.2 Infrastructure. Along the coast the infrastructure of the district is relatively developed, with road and air connections to Mombasa and Nairobi, the major urban centres of Kenya. Malindi is connected to various rural centres by earthen and gravel roads.
2.3.2.3 Sectors of the economy, income distribution and expenditure. The economy of the Malindi sub-district can be divided into three major sectors: (1) agriculture and animal husbandry; (2) fishing, and (3) trade, services and tourism. Industrially the district is underdeveloped.
Agriculture and animal husbandry provide almost 90 percent of the employment and income in the sub-district. Due to the fact that most of the small farmers do not hold legal titles to the land they cultivate, they are reluctant to change their cultivation patterns from subsistence to cash crops (60 percent produce only for subsistence, while 40 percent produce for subsistence and for the market). The result is an extremely low income for the small farmers (K.Sh. 500–3 000 (US$ 65–400)/household/year). This production structure also limits the domestic market potential of the area (only 15 percent of the population is involved in the monetary exchange).
Artisanal fisheries, the other traditional sector of the local economy, provides less than 5 percent of the employment in the sub-district. In the last decade there has been an increased demand which has increased the income of the average fisherman above the local (and national) average. Using only slightly modernized gear (the design of fishing craft has not changed at all), the artisanal fishermen, and especially the ones who own a boat, now realize a relatively substantial yearly cash income (between K.Sh. 2 500 and 12 000 or US$ 340–1 600). The landings are commercialized, mainly outside the district, by three commercial and one parastatal company. The development of a processing industry is not considered feasible because of the instability of supplies.
The tertiary sector (including the tourist industry) provides almost all wage employment in the sub-district (about 5 000–6 000 permanent jobs, directly and indirectly). Trade, services and tourism account for most of the economic growth in the district. Unlike the traditional sector, it potentially concentrates revenue for further investment and provides incentives for primary producers.
The disparity between this dynamic modern sector and a stagnating traditional production structure, between relative wealth in the urban centre and widespread poverty in rural areas, is also indicated in significantly different consumption patterns. Living mainly on home-grown staple foods, the family of the low-income small farmer consumes an insufficient amount of animal protein.
Summarizing the analysis of the local economy, the most significantly underprivileged population group consists of the small, subsistence-crop growing farmers and, only secondary, artisanal fishermen not owning boats and gear.
2.3.2.4 Social and cultural characteristics. Studying the social and cultural characteristics of the two population groups identified as economically underprivileged, the author found two considerably different socio-cultural systems.
The economically less deprived of the two groups, the artisanal fishermen, were ethnically almost 100 percent Bajuni. A case study of one of the typical fishing villages revealed a traditionally orientated and relatively closed society with an intact super-structure based on the Islamic religion and on traditional leadership. A pronounced cultural identity, stable value and behaviour patterns, and a strongly expressed individuality were complemented by a high self-assessment, to which the relatively high average incomes contributed considerably. Consequently, occupational mobility was low and the innovation potential of this group appeared to be marginal.
Quite contrary to the Bajuni fishermen of the Malindi area, the small subsistence farmers, who belonged almost entirely to the Mijikenda people, had no apparent religious or political superstructure. Their only cultural homogeniety appeared to be their ethnic origin. Their social organization was atomistic and corresponded to the scattered distribution of their settlements. Leadership structures were difficult to identify, and the author did not succeed in finding commonly shared value and behaviour patterns. The innovated potential was limited to the extent that there was an expressed fear of losing the existence minimum their subsistence agriculture provided by taking up something new. However, providing the demonstrated certainty they could succeed in another occupation, their innovation potential and occupational as well as geographical mobility had proven to be substantial. The major constraint limiting their initiative in this respect seemed to be the existential risk involved. Comparing the socio-economic and the socio-cultural characteristics of both population groups, the small farmers could be easily identified as the more adequate target group to be involved in the development of coastal aquaculture:
Summarizing, their needs could be reduced to the two crucial components of most rural development efforts in structurally underdeveloped socio-economies: the creation of employment and the generation of incomes.
2.3.3 The potential socio-economic impact of coastal aquaculture development
The case study assumed from previous studies, the technical feasibility of coastal aquaculture in the area and, through the analysis of the socio-economic reality, identified an adequate target group and its actual needs. Now we must examine the ways in which coastal aquaculture can possibly contribute to the objective implied above, while still exploiting the resources in a rational way.
To involve the indicated population group, as small-scale primary producers, directly in coastal aquaculture had to be disregarded following the results of the socio-economic and socio-cultural analysis:
An indirect involvement, as a wage labourer, therefore, would appear the only way to produce an immediate socio-economic impact. Once employed and paid on a regular basis, the small farmer could become acquainted with the new technology and could, by receiving adequate training, acquire the technical and commercial expertise enabling him later to become a fish farmer.
2.3.4 The social postulate
For the case discussed, we would formulate the social postulate for the development of coastal aquaculture as follows:
The exploitation of the existing potential for coastal aquaculture should, in its initial phase, use only a part of the area available. It should be undertaken labour-intensively and produce a maximum of permanent employment opportunities. Employees should be recruited from small farming families in the area and be given appropriate training throughout their employment period. Once qualified for the task, they should be provided with land, credit, and technical assistance, to enable them to undertake coastal aquaculture on their own (on an individual or on a cooperative basis). This procedure should be repeated until the existing land, suitable for coastal aquaculture, has been distributed and exploited to the extent where the largest number of families can earn a decent income without endangering the natural balance of the environment.
In the previous section we used a case study of an existing socio-economic reality to construct a social postulate for the development of coastal aquaculture to optimize the social benefits of such a development. Whether this postulate can be transformed into reality will depend on many factors which will be experienced only in the course of the proposed strategy. It also remains to be seen whether the proposed strategy actually proves to be adequate with respect to the reality the author attempted to analyse. Experiences in other countries, however, have proved two aspects of coastal aquaculture to be of special importance: an adequate legal framework, and an appropriate marketing system.
Coastal aquaculture is an established technology in many parts of the world, especially the culture of crustacea, and offers an impressive profitability to the investor due to high world market prices. Although initial investment is high, operating costs are low, especially in an extensive culture system where feeding and fertilizing are not practised. Suitable land can, in many cases, be purchased inexpensively, as mangrove areas do not usually offer alternative means of exploitation. Additionally, labour costs are usually low in structurally underdeveloped coastal areas because of widespread unemployment and underemployment.
Since the structural dichotomy of many developing countries tends to concentrate productive assets, surplus capital is often generated, waiting to be invested. Coastal aquaculture, undertaken on a profit-maximizing basis, offers an attractive investment opportunity for many private investors at present.
To illustrate the somewhat dubious effect such development would have for a national economy, we shall discuss a case where the development of coastal aquaculture was characterized by a demonstrated lack of national planning in general and socio-economic considerations in particular: the shrimp culture industry in Ecuador.
During the last ten years about 16 000 ha of Ecuadorian coastal areas were transformed into ponds to raise shrimp. This explosive exploitation of a natural resource was, and still is, carried out extensively, in ponds up to 70-ha large and without feeding and fertilizing. Pond construction was done by earth moving machines and filling and draining of the ponds by pumps. Estimates indicate that the initial investment required to construct 1 ha of pond and to operate it 1 year was between US$ 2 000 and US$ 3 000, while the gross return was sometimes up to US$ 4 000 at the end of the same year. Such profit margins lead to a total private investment of about US$ 40 million into the industry within the decade and resulted in an annual production of shrimp of 1 144 t (1976).
This spontaneous and unplanned development has caused severe environmental problems to the coastal strip, because mangrove areas are being deforested indiscriminately. Through the destruction of mangroves, small-scale industries which produced charcoal and tannin from the mangroves are diminishing, reducing income and employment opportunities along the coast. Furthermore, it is suspected that pond construction of the magnitude described endangers the breeding cycle of shrimp and many other marine fish species, thereby jeopardizing capture fisheries and the supply of shrimp larvae for stocking the ponds. At the same time, the shrimp culture industry has generated only a very limited number of employment opportunities for the local people, as pond construction and operation is mainly carried out by machinery. An estimated 2 000 artisanal fishermen derive their income from the capture of juvenile shrimp to be stocked in the ponds. The employment opportunities created attracted people who had been working in the banana plantations, because the shrimp industry offered better wages. This drain of qualified labour caused difficulties to the banana industry.
From the macro-economic point of view, it remains doubtful whether the production of shrimp and their export has produced an adequate impact on the national economy, i.e., by means of internal capital accumulation. Although most of the 263 companies which operate the ponds are national, they undergo regular taxation and probably reinvest a sizeable part of the revenues in the national economy. The export marketing is dominated by international private capital. Considering the high world market price of shrimp against the relatively low domestic price, we can easily estimate the profit margin of export marketing to be enormous. Whether these revenues are recirculated domestically is doubted by most of the persons who have studied the industry.
Ecuador has experienced the hazardous exploitation and, in some areas, partial destruction of a valuable national resource. This is due to the fact that no legal framework exists to regulate the explosive development of shrimp culture. A more rational distribution of the suitable land, an obligation to use semi-intensive or intensive culture practices, and limitations regarding maximum pond sizes would have resulted in perhaps a slower, but more balanced and less dangerous growth of the industry.
Directing the investors toward a more labour-intensive operation of the ponds would have created much needed employment for the local population. A nationally controlled export marketing would have ensured that the exploitation of national resources would contribute by recycling revenues, to the overall development of the economy.
We have discussed and roughly outlined the initial phase of the development of coastal aquaculture, and its planning with respect to possible and desirable social benefits. We have considered and extrapolated desired positive impacts and possible negative effects. However, our approach was that of the planner, the development expert, the policy maker. We have, although parenthetically, made the small farmer, the landless labourer, and the artisanal fisherman the ‘object’ of our approach to development. This reduction of the small producer as the target of the development effort may, or may not be legitimate for the initial planning of coastal aquaculture. Now, for its implementation, our approach will have to be supplemented with the realization that man is also the subject of development. Consequently, all efforts must be made to integrate the target population group actively into the process.
Considering all of the relevant economic, social and cultural aspects in the planning phase, and designing the development strategy according to the conclusions required considerable abstraction. Now, during implementation, the adequacy or inadequacy of the chosen strategy will be revealed as the abstraction faces reality. The strategy will have to be altered according to the exigencies, i.e., it has to be flexible. Above all, the acknowledgement of the individual members of the target group to be object and subject of the planned development must result in a socio-psychological approach to their involvement which stimulates and motivates the individual. Such an approach would include the promotion, among the target group, of awareness regarding constraints and limitations hampering social and economic progress of their families and communities and, consequently, their full participation in the planning and implementing of the development effort intended to improve their lot.
The active involvement of the people into the implementation of technological change, not only as an anonymous labour force, but as the implementing agents, will transform an exogenous innovation into an integral means of their struggle for a better standard of living. In the case of coastal aquaculture, the people must participate in the procurement of inputs and the commercialization of the produce, as well as in the culture operation. Only if the vertical integration of coastal aquaculture becomes transparent to those involved can they understand the causal connection of the different activities. A former farmer, fisherman, or worker becomes a fish farmer only if, through carrying out qualified work, he can identify himself with his new activity. If technological change eliminates the former professional identity, it must compensate for the resulting alienation of the individual by building up a new professional self-consciousness.
Another crucial factor in successfully implementing coastal aquaculture development is to gradually transfer responsibilities to the individuals involved. Experience has shown that successfully operating projects collapse and are abandoned because the project staff neglected to make the individuals involved carry out qualified tasks and the staff failed to delegate responsibility. If we expect coastal aquaculture to become, as a long-term objective, a means of rural development undertaken by the people, we must allow the people to experience the resulting benefits as well as arising responsibilities. A development project which reduces the function of individuals to assembly-line like activities will remain an external component of their lives.
Thus far, we have discussed some aspects of the implementing process which were relevant to the individuals directly involved in coastal aquaculture. Without doubt, each project will, during its implementation, face a variety of additional considerations and problems concerning its potential and intended role in rural development. Lastly, the success of a project in this sense will depend, apart from material inputs and technical assistance, on the factors roughly outlined in this paper: namely, adequate perspective planning and an implementation strategy which follows the postulated objectives.
If we innovate a technology in a socio-economic system, the technology, once it has become a productive asset to the economy, will influence and alter the system. On the other hand, the socio-economic system will determine the quality and quantity of the technological change. The acknowledgement of this interaction and the reflection of the socio-economic context of a project during its implementation will facilitate its integration. To become an integral element of rural development, coastal aquaculture has to interrelate with parallel efforts to improve the socio-economic structure of the society. With this horizontal integration into development plans which comprise, for example, land reforms, efforts to diversify production of overall strategies to become more self-reliant will increase the contribution of coastal aquaculture to integrated rural development.
A vertical integration of coastal aquaculture in the local economy would strengthen its role in the productive structure, and result in increased socio-economic benefits. Vertical integration can, to mention some possibilities, involve:
the use of waste products from other industries, as trashfish, slaughterhouse wastes, or agricultural by-products. This would, although to a limited extent, improve the rentability of those industries and, at the same time, exploit existing resources more productively;
the promotion of a local marketing system for the produce, which would provide further income and employment opportunities;
the encouragement of a locally based processing industry, which would, apart from again creating employment, increase the quality and marketability of the product.
Coastal aquaculture can increase its range and effectiveness considerably if it is integrated into an overall structural development. At the same time, horizontal and vertical integration of coastal aquaculture will transform a technical innovation into a strong and balanced constituent of a diversified and self-reliant rural economy.
by
M. Pedini
Fishery Resources Officer
Inland Water Resources and Aquaculture Service
FAO, Rome
1 Published also in 1981 as FAO Fisheries Circular 732, 14 p.
Penaeid shrimp culture is becoming increasingly important in tropical developing countries with suitable areas for culture and fast growing species. Problems in the existing fishing grounds due to overexploitation led to development and refinement of cultural practices in many countries. The current practices of penaeid shrimp culture in tropical countries are discussed and examples are given on the techniques involved and production obtained in Southeast Asia, India and Latin America.
Problems that have arisen concurrently with this development as the utilization of the mangal ecosystem for conversion into ponds, and the problem of not totally suitable techniques for culture in potential acid sulfate soils are dealt with. The Ecuadorian province of El Oro is taken as an example of the first problem, while the Philippines have provided the subject matter for the second problem. Alternative strategies are suggested in order to avoid the repetition of the same mistakes when planning the development of new virgin areas as could be the case of African countries. As a final point, the development of hatcheries to supply seed for new areas to be developed under intensive management, and to act as seed banks for distribution of seed to farmers, is contemplated and the new developments are reported.
Penaeid shrimp are one of the important resources of the coastal fisheries, and in terms of value per unit catch and total value of the catch on a worldwide scale, are surely among the most important as they are considered a luxury food commodity in international trade.
Although penaeid species are found in all the seas of the world up to subpolar latitudes (Wickins, 1976), their distribution is mainly tropical and subtropical. The majority of the species of high commercial interest and the most productive fishing grounds are found between the tropics.
The high demand for shrimp from the developed industrialized countries, especially the U.S.A. and Japan, has been - since the beginning of the fifties - a strong incentive for developing countries with good shrimp fishing grounds to concentrate on this fishery in order to export the product and obtain valued foreign currency. The two countries mentioned above (U.S.A. and Japan) absorbed up to 80 percent of the total world production of frozen shrimp (Shigueno, 1975).
This high demand and the high prices brought by frozen shrimp in the international markets have led to a rapid increase in the number of shrimp trawlers in the fishing fleets of developing countries, not accompanied, however, by stock assessment studies or by sensible restrictions in the allowed catches in most cases. Processing plants have followed the development of the fishing fleets, and they have been forced to improve the quality of their frozen products in order to comply with rising standards, especially sanitary, demanded by the countries that absorb their product.
The massive exploitation of this coastal resource has led to situations in this decade in which, as a result of overfishing of fishing grounds in countries that allowed an indiscriminate growth of their fishing fleet, some of the stocks have been depleted, are decreasing or - in the best of the hypotheses - have reached their maximum sustainable yield. This does not mean that areas in which increased fishing pressure is possible no longer exist, although other circumstances not directly related to the area itself may endanger their development. Amongst these external sources of stress for the fishing industry the more important are the increased operating costs due to the energy crisis, and rising inflation (this being more acute in many developing countries). The increase in pollution of the coastal areas in some developing countries due to growing industrialization and urban pollution is another key factor which affects primarily the nursery grounds of the penaeid shrimp thereby reducing recruitment. The combination of these factors makes the development of fishing grounds more difficult as time goes by, but at the same time increases the chances of shrimp culture development so that this receives more and more attention both from the public and the private sectors.
Shrimp culture is a relatively recent practice, and commercial shrimp culture can be dated from the beginning of the sixties (Shigueno, 1975) in Japan, although in several countries of Southeast Asia the trapping and growing of penaeid shrimp in intertidal ponds has been a traditional practice for several centuries. Regarding Latin America, where shrimp culture has also taken a strong foothold, the commencement of activities can be dated from the late sixties (Cobo Cedeño, 1977). Africa, in spite of the existence of coastal areas with good potential for development and the presence of species which are successfully cultured elsewhere, has not developed shrimp culture to any significant extent. A few trials have been carried out only in Tunisia (Brunel, 1976) and Ivory Coast (Griessinger, pers.comm.).
Industrialized countries like the U.S.A., Japan and some European countries have devoted great efforts and funds to the development of shrimp culture. The results up to now have been to a certain extent successful only in Japan, where about 1 000 tons of cultured shrimp are now produced each year. This is due to the very special internal market for shrimp which, having very high prices for live Kuruma shrimp, Penaeus japonicus, can support an industry with very high production costs. Besides their culture operation for the table market, the Japanese are also involved in very ambitious projects for restocking the Seto Inland Sea with millions of postlarvae and juveniles in order to improve the catches from their shrimp fishing grounds. Positive results have still to be proved.
In the U.S.A. and in Europe, the lower market price for shrimp makes the whole cultural operation uneconomic, although a great deal of technology has been developed. For these countries it is now a question of refining the existing know-how in order to lower the production cost so as to be competitive with the prices of landed shrimp. This is a most challenging endeavour and rising inflation is pushing many investors to tropical countries where existing techniques can be adapted and lower production costs can be expected.
Many advantages do exist for the establishment of shrimp culture in the tropics as well as some disadvantages, but the former seem to outnumber the latter, at least for the numerous local and foreign entrepreneurs who have entered this field in the last ten years. Firstly, the tropics are the natural habitat of the majority of the fast growing species of penaeids and thus a supply of gravid females, and in many cases abundant wild fry, is guaranteed. This would be the case of India, countries of Southeast Asia and in Latin America, as well as Africa. The tides are another positive factor. Tides from 2 to 4 m are not uncommon in the tropics. This allows the filling and draining of tidal ponds without use of external energy for pumping thus lowering costs. Also, land is less expensive and more available, and due to the interest shown by many governments, coastal areas on lease are obtained relatively easily. There is an abundance of labour at low cost. Taxation is also mild. These factors, positive for the development of the industry, have backfired in some cases where development has been too rapid and indiscriminate, creating local problems which are difficult to solve. We will come back to this point later on.
As examples of the existing diversity in shrimp farming, we will briefly discuss the current cultural practices in some countries of the tropics. However, before describing the different types of culture the correct terminology should be established. In order to standardize criteria we will follow the terminology used by Ravagnan (1978), cited by Ardill (1979). We will call it intensive culture when all nutritional needs of the organisms cultured are coming from external sources; semi-intensive culture when part of the nutritional requirements come from the environment (pond or natural lagoon), and extensive when no fertilization or feed is used to supplement the natural production of the cultural environment.
Amongst the Southeast Asian countries, Thailand is the one that has developed the mono-culture of penaeid shrimp to a larger extent. The main part of the cultured Thai shrimps comes from extensive ponds that cover over 12 000 ha (ASEAN, 1976). The average production is on the low side, and due to the lack of proper records the figures reported are quite different. Figures ranging from 25 to 625 kg/ha/year have been reported (Anon., 1973), but Teinsongrusmee (1970) reports average production per year of 338.75 kg/ha for the central areas of Thailand. More recent papers report average production of 109 kg/ha/year (Pongsuwana and Bhukaswan, 1977).
The average size of the ponds is 10 ha (range 2–80 ha). They are shallow ponds with a depth of water from 10–40 cm in the flat central area and up to 1.5 m in the peripheral canal. The ponds are sited in intertidal areas and the tides are used to fill and drain them. Pumping is frequently used to fill the ponds to a level above high tide (Padlan, 1979) and especially to increase the stocking of postlarvae and juveniles. No fertilizer or supplemental feeding is added to the ponds in most cases. The main species cultured are: Penaeus merguiensis, P. monodon, Metapenaeus brevicornis, M. ensis and P. indicus. More recently, intensive culture practices have started using hatchery reared postlarvae of P. monodon (Kunvankij et al., 1976), stocking them at densities reaching 60/m2. The feed used was trash fish, crab meat, mussels and rice bran. Production of P. monodon was 5 100 kg/ha in 225 days in one trial using a pond of 0.48 ha, and 2 544 kg/ha after 165 days in a second trial in the same pond, but using a lower stocking density of 21 postlarvae/m2. The mortalities experienced were fairly high: 78.8 percent in the first case and 61.8 percent in the second trial. However, the total production of the pond was much higher since other species of shrimp were harvested as well as crabs and sea bass, raising the total pond production to as much as 13.3 tons/ha for the 14-month culture period.
This example has been included as an indication of the potential productivity with intensive management, but extrapolations for investment planning over large areas must be avoided because the expansion of this type of culture would necessitate such inputs in terms of post-larvae and feed that will be rather difficult to meet at present and in the near future.
The Philippines and Indonesia share a similar system in which penaeid shrimp, mainly P. monodon and P. merguiensis plus small shrimp of the genus Metapenaeus, are cultured as secondary crop in milkfish ponds. Vast areas are available for this type of polyculture (180 000 ha of tidal ponds in Indonesia and 176 000 ha in the Philippines), but the average production reported is rather low, ranging between less than 100 kg/ha/year and 300 kg/ha/year. The average pond in Indonesia has a surface area of 2–3 ha, a depth of 30–50 cm in the flat areas and 75 cm to 1 m in the peripheral canal. They are filled by the tide which also carries in the postlarvae and juveniles of penaeids. The fry gatherers working for the milkfish industry also collect postlarvae of P. monodon for stocking in ponds. The type of management of these ponds is mostly extensive. At present, efforts are made by the Government of Indonesia to develop hatcheries and semi-intensive systems of culture, this latter aided by the FAO/UNDP Project. Promising results have been obtained.
In the Philippines, the average pond is a little larger (4–5 ha) with depths of 0.5 m in the flat area and 1–1.5 m in the peripheral canals. Different size ponds are used: nursery ponds where initial stocking densities are high (40 000/ha), and growing ponds in which much lower densities are used (2 000/ha).
Fertilizers are used to enhance the natural food production and the ponds are managed in such a way that the growth of “lumut” (a complex formed by Chaetomorpha spp. and Enteromorpha spp. algae) is favoured. This could be described as a semi-intensive management. As well as in Indonesia, substantial effort has been devoted in the last years to the development of hatchery techniques and more refined methods of pond management.
A more extensive type of shrimp culture is practised in Singapore and Malaysia in trapping ponds. These are ponds ranging from 4–50 ha with a depth of water of 0.5 m in the flat area and as much as 2–3 m along the peripheral dykes. The tides provide the fry stock and there is an almost continual collection at the spring tides by bagnets installed in the sluices during the outflow of the water. The control of the pond condition is minimal but this continuous process of stocking and harvesting gives fairly good results with production reaching up to 700 kg/ha/year in Johore Province, Malaysia. Some control on the predators that enter the pond with the shrimp during the periods of high tide is practised by using tea seed cake. However, this trapping method is practised in a limited area (≃ 800 ha).
India is another country in Asia where shrimp culture is practised over a large area. In this country several stock assessment surveys have been carried out and the conclusions are that the commercial shrimp fisheries (very important, and with most of the catch exported) have reached their maximum in certain fishing grounds. This obviously favours the development of shrimp culture and substantial efforts are made to improve the extensive type of management of the over 14 000 ha of paddy fields and backwaters existing in the state of Kerala (4 500 ha) and brackishwater ponds called “bheris” in West Bengal (9 600 ha) (Anon., 1978). The traditional culture practices are similar in a way to the trapping ponds of Malaysia and Singapore with continuous stocking and harvesting and a very short period of culture. Figures as high as 1 500 kg/ha/year have been reported, but more normal values range from 500 to 1 200 kg/ha/year. In the seasonal culture type practised in paddy fields, rice is cultivated during the monsoon from June to September, and shrimp from October to May. As well as in Malaysia and Singapore, many predators may enter the ponds together with the shrimp postlarvae and juveniles as no adequate screening of water is practised.
In Latin America we have examples of shrimp culture in Mexico, Panama, Costa Rica, Ecuador and Peru. In all these countries the development of shrimp culture as such is a relatively recent event, and can be dated as starting in the second half of the sixties, with the exception of Mexico, where the very extensive lagoon fishery called “tapos” are a tradition. Three different types of shrimp culture can be recognized in Latin America: first the very extensive lagoon fishery of the “tapos” where existing coastal lagoons are managed as enormous ponds by placing screens and controlling to a certain extent the intake of postlarvae and juveniles, and blocking them inside until harvest time. Second is the method practised in the pacific coast of other Central American countries, like Panama and Costa Rica, that mixes U.S.A. hatchery techniques for production of postlarvae, with tidal ponds in the Southeast Asian style with improved semi-intensive management. The third method is the one practised in Ecuador and in Peru where marshes and mangrove areas have been transformed into ponds, in most cases with pumps for water control, and using wild fry as stocking material. This is another case of extensive management.
The “tapos” fishery has been studied in detail by several Mexican authors whose contributions have been reviewed recently by Edwards (1978). The total production (1974) for the coastal lagoons amounts to 15–20 percent of the total catch on the Pacific side and the species harvested are P. stylirostris in the lagoons with salinities near sea levels (from Sonora to Baja California) and P. vannamei in lagoons with lower salinities (Sinaloa - Nayarit states). A good example of this fishery is the lagoon complex Huizache-Caimanero in the state of Sinaloa. The mechanic of the “tapos” is the following: a screen barrier is placed across the channels leading to the lagoon in mid-August. This barrier has several collectors, which are sort of traps, where the shrimp concentrate and are fished during their emigration toward the sea. The fishery starts in September and goes on to early January. There is a closed season from mid-April to mid-August in which the “tapo” is dismantled to favour the immigration of postlarvae and juveniles into the lagoon. Once the “tapo” is in place the shrimp cannot get out of the lagoon in which they have been feeding during the juvenile phase until the onset of their emigration to the sea. Due to the very large size of these lagoons, no other form of management is possible at present without large capital investment, and the production is greatly influenced by the weather conditions of the year. However, the average production can be estimated at around 100 kg/ha/year, although the prospects for improvement are considerable both through refinement of the tapos management (as a result of the better understanding of the bionomics of the species involved) and through intensification of the cultural practices in the peripheral areas of the lagoons, starting by improvements in the control of predators, and using wild fry as stocking material.
Ecuador started the development of shrimp culture in 1968 by building the first ponds in salty marshes of the El Oro province. The expansion of this industry has been tremendous and by 1978, 213 companies existed with concessions for pond construction covering over 16 000 ha (Anon., 1978) although not all of them are operational. The production has risen at the same pace, growing from 45 tons in 1972 (Cobo Cedeño, 1977) to 1 144 tons in 1976.
The areas selected for construction of ponds have been the “salitrales”, alluvial salty soils adjoining the mangals of El Oro, Guayas and Manabi provinces. These areas have access to fresh and brackish water due to their proximity to the mangals, and are flat and deprived of vegetation so that construction of the ponds if facilitated. Cobo Cedeño (1977) has described in detail the system used for shrimp culture in Ecuador. The ponds are large, measuring from a few hectares to more than 70 ha (Neal, 1976) and initially were built by digging a peripheral canal to build the dykes, which left a wide, rather shallow central area. Pumpe of large sizes are used to fill the ponds, but considering the size of the larger ponds, are surely insufficient to ensure a rapid exchange of water in emergencies that may arise, like low values of dissolved oxygen or phytoplankton blooms. No hatcheries are used to produce the seed, which is collected by hand from the wild during the peak seasons in the channels of the mangals and in artificial channels built in the mangals and near them for this purpose. The main species collected and cultured is P. vannamei, of which it is reported that 20 000 to 40 000 postlarvae or juveniles are stocked per hectare. However, this does not take into account the number of postlarvae that enter the pond during the pumping. Some rough screening of the pumped water is made, but predators - especially in larval forms - still enter the ponds. The management of the pond is extensive, and the high fertility of the water of the mangals, as well as of the soils, accounts for the rather good production that is reported to be on the average between 300 kg/ha/year and 450 kg/ha/year (Neal, 1976). Not all the concessions (16 000 ha) are in full operation and thus the total production in 1976 was 1 144 tons. The new and future developments include the construction of hatcheries for seed production due to the increasing scarcity of wild seed in the El Oro province and improvements in pond design, using heavy machinery to build the ponds, levelling soils and lowering the flat area so as to get deeper ponds. Since harvesting the larger ponds has always been quite difficult, it is foreseeable that new developments will limit the size of ponds to surface areas below 10 ha.
The rapid development of shrimp culture in Ecuador has been rather uncoordinated by the public sector and thus serious problems have arisen. To start with, the area of “salitrales” in the El Oro province has been the most heavily reclaimed so that all the 7 540 ha available have been conceded and some 2 500 ha of the existing 22 000 ha of mangal have been deforested for conversion into shrimp ponds, while concessions on 5 180 ha have been given for the Guayas province “salitrales” where 30 000 ha are reported to be available.
This overcrowding of ponds in El Oro province is worrisome due to the fact that the deforestation of the mangals has commenced, as these are the natural habitat of postlarvae and juveniles of penaeids during these phases of their life cycle, and are the place where they find food and shelter before their emigration to the sea. The reduction of their habitat and the increase in demand for wild postlarvae and juveniles for stocking purposes in the newer ponds has already created some problems, which will increase in the future if the operation is intensified and more mangal is converted into ponds.
Taking into account a stocking density of 35 000 postlarvae and two crops per year and per hectare, it has been calculated (Anon., 1978) that for the 16 100 ha of pond concession a maximum amount of 1 100 million postlarvae would be required. From studies carried out by several authors in Mexico, in the lagoon complex of Huizache and Caimanero, it appears that the population density of the postlarvae and juveniles of the penaeid species present in the lagoons, the same as in Ecuador, varies from 0.3 individuals/m2 in the flats of the lagoon to a maximum of 1 individual/m2 in the zone of the channels surrounding the mangal, that appears to be the preferred habitat (Edwards, 1978).
If we extrapolate this situation to the Ecuadorian mangals, with due caution, and assuming that the population densities should be similar, we find for the El Oro province (22 500 ha of mangal) a maximum of 225 million resident population of postlarvae and juveniles. If this province would exploit the 10 000 ha of existing concessions at the densities mentioned above, it would require 700 million postlarvae to stock the ponds, a figure that possibly could not be met by the existing population which could provide seed for about 3 200 ha. Although too many assumptions are implied in this reasoning, due to the lack of data on the bionomics of these penaeids in Ecuador, it may help to explain the already existing problems of obtaining enough seed for stocking in this area. Apart from the fact that some decrease in future recruitment in the area could be expected if the fishing mortality (for stocking purposes) on the natural population of postlarvae would exceed 90 percent. This percentage has been estimated as normal mortalities for the period spent by P. vannamei in coastal lagoons and mangrove areas in Mexico (Edwards, 1977).
This uncontrolled rapid development has been caused by the lack of control on the release of concessions by official institutions, and especially due to the lack of coordination between the two main institutions involved, the Dirección de la Marina Mercante (DIMERC) which has jurisdiction on the beaches and mangroves up to 8 m inland from the line of the highest tide, and the Instituto Ecuatoriano de Reforma Agraria (Ecuadorian Institute for Agrarian Reform) that can release concessions for “agricultural” use from that limit. Cases of illegal appropriation of mangal areas and “salitrales” have also taken place.
Furthermore, the rapid development of this industry, has diverted part of the labour working in the banana plantations, as qualified labour, to the shrimp farming industry, as unqualified labour, due to the higher earnings, but creating a socioeconomic problem to the banana industry and raising in general the cost of labour.
In a situation like that, in which the capital invested could be estimated to be between 34 and 45 million dollars, the risk that an excessively rapid growth, not properly planned, could lead to a sudden collapse due to the lack of seed for stocking, creating serious socio-economic problems, is high. This aspect is treated more in detail by Schmidt (1979).
The Peruvian situation shows some similarities with that of Ecuador. Shrimp culture in Peru is limited to the areas around the mangal of Tumbes, that could be considered the natural continuation of the El Oro mangals. The suitable area available is more reduced, covering 3 000 ha. The type of culture practised is similar to the Ecuadorian and although the development of shrimp farming started three years later than in Ecuador (in 1971) the same explosive development has taken place, leading to similar problems.
In Central America, Costa Rica and Panama also started shrimp culture at the beginning of the seventies. However, in these countries there was a transfer of know-how from the U.S.A. that resulted in more sophisticated cultural practices than the ones described above. In both countries the development of shrimp farming has taken place along the Pacific coast which offers better tidal ranges for the culture. Also, in both cases, the development has been limited to a few hundred hectares of ponds, although there is still considerable potential area for development (in the case of Panama, around 8 000 ha - Pretto, personal communication).
Hatcheries have been developed for the production of seed using the techniques developed in the U.S.A. for mass production of postlarvae. Unfortunately, being private companies, very little information is released as it is considered propietary, and almost no data exist on the results obtained.
In Costa Rica more than 100 ha have been cleared and converted into ponds, and it is known that the cost of construction has been much higher than estimated. Problems associated with potential acidic soils common in mangrove areas have also arisen, making more difficult the normal operation of the ponds, and requiring frequent flushing of the ponds.
It is easily foreseeable that the economically appealing shrimp market will attract more countries with potentially good areas and suitable species into the practice of shrimp farming. Africa, being a practically virgin area has the greatest potential for development, and it would be desirable that in planning their shrimp farms the African countries incorporate the lessons provided by the past experience in other parts of the world and thus avoid the repetition of the same mistakes.
In countries where large areas are already under culture, as in Southeast Asian countries, efforts have been directed towards giving general recommendations and technical instructions on how to manage shrimp ponds. ASEAN has been very active in this respect in the last four years, and as a result many documents have been produced, including a manual on the culture of penaeid shrimp (ASEAN, 1978). Although the author's feelings about these initiatives are generally positive considering the technical details and advice contained in this literature, planners should handle it with care and not consider it as recipes which will lead to the best results. Initially, it must be taken into account that these are documents directed at countries where the development (mainly intended in terms of construction of the ponds) has already been carried out, but not always in the best possible way, and are sometimes aimed at improving the existing conditions. Therefore, the development of virgin areas should be started with an open mind not simply directed at copying existing models. More broad and scientific criteria may help to adapt the positive points of the different techniques to the particular characteristics of every site or area, and to discard the practices which have shown exceedingly weak points in other places.
Needless to say, not only technical aspects have to be considered, but being an industry that generates cash income rather than food to the farmers, the socioeconomics of the area which is meant for development have to be carefully considered. The present paper will not deal with these aspects which will be treated elsewhere, but the author stresses the importance of conducting socioeconomic studies of the areas to be developed prior to any large scale planning.
Another important factor to consider is the need for the governmental institutions to keep a tight control on the areas to be developed and to set a coordination mechanism in case more than one governmental institution is involved. This would prevent situations of explosive development as in Ecuador that later on are very difficult to correct, and which can risk the failure of an activity that had very good chances.
Parallel to the development of one area, or even better prior to its development, studies have to be carried out in the area to as certain the amount of land available, the tidal ranges, the nature of soils (a most important factor), the quality of the water available, and the proximity of nursery grounds. Concerning the last point, an attempt should be made to quantify the availability of wild seed over a full representative cycle. The variations in the meteorological conditions have to be checked for at least a full year if historical records over extended periods are not available, as well as the availability of fresh waters. The time spent in these preliminary studies will pay in the long run since they will help to decide the most appropriate type of management for the local conditions, rather than to adopt a technology developed for other areas, which may prove too unsuitable under the local conditions.
Regarding the selection of sites for placing the ponds, the mangals have been too often a target area. In some cases there has been no other choice, as in the densely populated countries of Southeast Asia, but their conversion into fish and shrimp ponds or more generally their exploitation and deforestation pose several serious questions that are not yet answered. Christensen (1979) has produced an interesting paper in which the alternative uses of the mangal are studied in detail for the Chanthaburi province in Thailand.
It has been clearly shown by many authors that the mangal ecosystem plays a significant role in the life cycle of many of the economically important species of penaeid shrimp. One of the salient characteristics of this ecosystem is the high primary productivity of its benthic community for which figures of 5.6 g C/m2/day have been reported (F. Golley, H.T. Odum and R.F. Wilson, 1962). The mangrove trees provide an enormous quantity of organic matter as detritus, mainly in the form of leaves (E.J. Heald and W.E. Odum, 1970), which are colonized by bacteria and especially by fungi which initiate the process of decomposition of this organic matter and convert it into microbial and fungal biomass. By feeding on this detrital matter, enriched by the bacteria and fungi growing on it, the juvenile shrimp, that can be classified as opportunistic omnivores, gain the main part of their protein diet (Odum and Heald, 1972; Adams and Angelovic, 1970). Recent experiments (Edwards, 1977) show that when growing juvenile phases of P. vannamei in cages on the bottom of coastal lagoons in Mexico, at densities of 2.5 individuals/m2, the growth observed, 0.88 mm/day, was similar to that obtained in marking and recapture experiments in the same lagoon. When the cages were lifted 30 cm from the substrate, growth was negligible (0.03 mm/day) although all specimens survived and were in good condition. This fact proves that juvenile shrimp of this species need a substrate highly rich in organic matter for proper growth.
The effect of the intricate roots of the mangal ecosystems for juvenile forms must also be taken into account as shelter against predation.
These points would support the conservationist ideas of mangal preservation, since they can, in certain cases, support populations in excess of 1 juvenile/m2, and are therefore an important source of seed for the industry.
It seems therefore that an ideal situation is found when ponds can be built in flat areas deprived of vegetation, as the Ecuadorian “salitrales”. However, in the cases where mangals are going to be converted into ponds, previous planning will be needed to determine the total area that can be converted as a function of the amount of wild postlarvae that the rest of the mangal could provide for stocking the ponds. Spacing of the farms with mangrove areas in between would also be desirable.
A further point that must be considered is the arguable adequacy of mangal areas for conversion into ponds, apart from the considerations of their value as nursery grounds. It appears that in many areas of Southeast Asia and Central America, where mangals have been converted into fish and shrimp ponds serious problems have been experienced. Firstly, with the excessive clearing and excavation costs due to the amount of roots that have to be removed; and secondly with soil and water quality related to the problem of potential acid sulfate soils, and the traditional management practice of periodic draining and drying of the pond bottom soils, that in the case of potential acid sulfate soils will transform them into acid sulfate soils.
It has been previously mentioned that the mangals show very high figures of benthic primary productivity, due to the input of decaying organic matter from the trees and the associated microbial and fungal biomass. This suggests a high oxygen demand in the benthos that may, in many occasions, lead to development of anaerobic processes. In these cases, sulfur bacteria become active and use sulfates (normally present in brackish water in concentrations higher than 300 mg/l) as a hydrogen acceptor, to oxidize the organic source of energy, and reduce the sulfates to sulfides (Ivanov, 1968). The sulfides either accumulate as hydrogen sulfide gas in the soils or combine with iron to from the mineral pyrite that accumulates in soils. If these soils containing high amounts of pyrite are exposed, the mineral is oxidised producing a very acidic reaction from which sulfuric acid is produced and active iron is liberated. The acid lowers the soil pH and after the pond is filled it is diluted in the water causing a drop in pH which is unbearable by most aquatic organisms. In the soil the acid attacks minerals liberating, apart from iron, aluminium and manganese in active form, which combine with inorganic fertilizers trapping them in the bottom of the pond as insoluble compounds, thus preventing their use by algae.
Since this problem was discovered, the remedy applied has been to flush and dry newly constructed ponds for extended periods until the pyrite is leached out of the soil, or to apply lime to neutralize the acid. Liming is a very expensive method due to the lime requirements of this type of soil and, for example, Potter (1976) estimated that well over 20 tons/ha was required for a site in the Philippines. Neither method is satisfactory. Furthermore, since the dykes of the pond are made of the same soils as the bottom, another problem appears associated with rains. During the dry period, pyrites are oxidized which can lower the soil pH to values below 4 which in turn inhibits the growth of grass on the banks, that would limit erosion. When the rains come, the acid material is flushed into the pond, lowering the pH of the water, and causing fish and shrimp kills. Potter (1976) summarized the problems encountered in ponds built on potential acid sulfate soils in the Philippines. They have poor fertilizer response and low natural food production, resulting in slow growth of the organisms cultured. Acid runs off after heavy rains, causes mortalities of fish and shrimp and there are serious problems of dyke erosion.
All these points tend to indicate that the traditional pond construction and management practices in mangrove areas should be reconsidered for these special areas presenting potential acid sulfate soils. Simple analytical procedures have been developed (Potter, 1976) to test the degree of potential acidity that can be expected from a soil before the excavation of the pond, so that it would be possible to decide first if ponds should be constructed, secondly the most appropriate type of construction and lastly the most effective type of management.
Since the remedial measures tested so far have not yielded any good results, perhaps a total change in the type of management could be a more appropriate answer, if it is decided to use a mangal area that has shown an acid sulphate soil reaction.
Frequently, areas with superficial soil of low potential acidity may overlay soils with much higher potential acidity, which once the upper layer is removed by digging the pond, are exposed and concurrently oxidized.
What the author would propose for these areas is to abandon the practice of total excavation to construct pond area that can be filled by tides, and revert to the construction of a peripheral canal to raise the dykes, minimizing the disturbance of the good surface soil of the central part, from which however mangrove trees and big stumps should be removed. Filling of the pond could be done by pumping in cases where tides are insufficient to maintain a water depth of 50 cm over the central elevated portion of the pond. Cook (1976) has discussed the pumping versus excavation hypothesis mostly from the economic point of view, and according to him for Malaysian conditions it could also be more economic to pump water to maintain the water level, apart from other listed advantages of such a type of pond. From the point of view of management of potential acid sulfate soils, this practice would leave the deeper layers of the soil undisturbed, and being waterlogged they would not oxidize. In addition, the traditional practice in some countries of periodic drying of the pond bottom as well as the practice of fertilization with inorganic fertilizers, that can be trapped in these soils, should be re-examined.
In a certain way, improvements in management could be possible by:
use of pumps for filling the pond and renovating and aerating the water;
by giving supplementary feeding instead of fertilizers; and
practising a programme of continuous stocking and harvesting of the pond.
A further point is that by leaving a top layer in the central part of the pond and by offering the feed in the peripheral areas, the on-going process of organic detritus decomposition by fungi and bacteria could continue in the central part, thus providing a natural protein for the stocked postlarvae and juveniles.
Of course, this is not a magic recipe and it can be seen only as a suggestion for areas with potential acid soils. The problem of acid leaking from the banks and erosion remains, although Potter (1976) has suggested the use of African star grass Cynodon plectostachyus, an acid resistant grass, as a possible means to ease this problem.
It is easily foreseeable that great changes in cultured shrimp production are not likely to happen in the next five or ten years, considering the already large size of this cultural practice and the number of farmers involved, especially in India and the Far East, but there is still room for improvements in the efficiency of the existing practices in every country, improvements that will require good extension services to help the farmers. There are still areas that could be converted into ponds, although in some places these areas are mangals and with the growing awareness of their importance from an ecological point of view, some reluctance to their release for conversion into ponds can be expected, thus limiting the expansion.
Regarding the source of seed, wild seed will continue to be the main supply, although more and more hatcheries will be developed as the techniques for induced maturation of parental stock are perfected, more knowledge about disease prevention and treatment is gained, and survival rates are improved through development of more reliable production techniques, lowering the cost of production of postlarvae to acceptable levels for the farmers.
The possible improvements for the extensive and semi-intensive practices will require a certain amount of applied research in several fields such as control of pests and predators, bionomics of the species involved (in case of exploitation of coastal lagoons through systems similar to the “tapos” fisheries) and fertilizer effects in brackishwater ponds, in order to improve production without raising the cost. It is felt that the simplest initial step could be done through development of selective screening systems in the ponds that are filled and emptied periodically by tides as in Malaysia, or where pumps are used to fill them as in Thailand or Ecuador, as limiting the predation would increase survival of shrimp. Another simple step would be the shortening of the period of culture in the ponds, or - to put it in a different way - to have continuous harvesting and stocking, whenever possible. It has been debated for a long time whether it would be desirable to grow large or small size shrimps. Although the price of large shrimp in the market is higher than for the small shrimp, the total revenue from a pond could be higher as the production of small-size shrimp will also be higher than that of large-size shrimp. This point has been dealt with in more detail by Cook (1976) and readers are referred to this very interesting paper.
Regarding the effects of fertilizers, both organic and inorganic, in brackishwater ponds, and the understanding of their dynamics in the pond which could lead to more scientific and simple recommendations on their use, it is felt that this is a longer term endeavour, but a necessary one. In this respect, brackishwater pond research lags far behind that of fresh-water ponds, and more effort should be devoted in order to avoid unnecessary waste of fertilizers and the resultant increase in production costs.
It is perhaps in this field that more diverse and subjective recommendations have been made. The past trial and error procedure applied in some countries like Indonesia and the Philippines to find appropriate fertilizer dosage cannot be accepted as recommended doses for other areas even in the same countries, as the reaction of the ponds in terms of productivity may be very different from what is expected. It is now also obvious that substantial amounts of fertilizer, every day more valuable, have been lost when fertilizing ponds built in acid sulfate soils.
Perhaps it would be opportune to mention here that we are still lacking an understanding of the pond ecosystem as a whole, in order to be able to assess the relative importance of the different cycles on the pond ecology and thus be able to take decisions for management purposes. Attempts to establish mathematical models have been started, necessarily simple now and susceptible to much improvement (Cassinelli et al., 1978), but this line of research is to be encouraged. In the long run, the basic knowledge gained could be used by the industry and in different regions by utilizing local parameters in the models. Another good point about this sort of exercise is that it will identify the priority areas that require more research in order to improve the fitness of the models.
Shrimp hatcheries are a clear need where intensive management of shrimp ponds over not too large areas, in the order to a few hundred hectares, are envisaged. In these cases, large quantities of shrimp postlarvae or juveniles of the same age, needed to reduce problems of cannibalism due to the high stocking densities, cannot be practically obtained from the wild in a very short time. This would require employing a large number of workers, and it is therefore necessary to resort to the synchronous production of batches of several million postlarvae in some cases.
Several types of hatcheries have evolved since the initial developments in Japan, and it can be said that a continuous refining process has been going on since then in order to lower the cost of the postlarvae produced, which has been high from the beginning.
The development of hatchery techniques had two main bottlenecks in the past which for a long time had prevented their economic operation. One was the need to obtain gravid females from the wild, requiring renting or purchase of trawlers to obtain a few adequate specimens per fishing operation, a rather questionable procedure from an economic point of view. The second point has been the dependency of the hatcheries on the many times scarce and too expensive cyst of Artemia salina as a main food item for the carnivorous larval stages.
Recent development seems to throw some relief on these two aspects and will contribute to the expansion of the hatcheries in many countries.
Regarding the first problem mentioned, eyestalk ablation in some tropical penaeid species has been the tool to obtain induced maturation in parental stock kept in captivity. However, it was necessary to perfect the techniques of broodstock maintenance and only recently (Halder, 1978; Santiago, 1977; AQUACOP, 1977, 1979) have papers reported the techniques for closing the cycle of cultured penaeid species as P. monodon, P. vannamei and P. stylirostris. No doubt these reported techniques are still perfectable and will be perfected but the dependency on wild gravid females can now be considered as belonging to the past.
As far as the second problem is concerned, the pressing need to reduce the amounts of A. salina nauplii to be consumed by the larval shrimp, due mostly to their scarcity, led to detailed studies of the nutritional requirements of the shrimp (although not yet complete) (New, 1976) in order to prepare artificial diets and, another line, to find feed cultures that could be produced locally from inoculums (mainly rotifers and copepods) and be cheaper than the imported A. salina cyst. New sources of A. salina cyst have also been identified in other countries than the U.S.A., and techniques are being developed for inoculation of salt ponds with cysts in tropical countries during the dry seasons, in order to produce enough cysts for the local needs, so that very likely the price of packed cysts will come down as the competition increases and it will be possible to become independent of the supply of cysts by using inoculation techniques.
Another relatively important point that had reduced the effectiveness of hatcheries in the past in terms of survival was the tendency to keep postlarvae for about 15 days or more in the tanks (until reaching a P15 stage) and after this period to stock them in the ponds, with the result that the tanks had lower production in terms of batches produced per year, and there were high initial mortalities when stocking the production ponds. These difficulties have been eased by the development of techniques for nursing the postlarvae in specially designed raceways (Mock et al., 1973) at densities up to 10 000/m2, until they reach a pond stocking size of 2 cm. By using this nursing technique, the larval rearing tanks can produce more batches per year and the overall efficiency is improved since also a higher survival rate in the ponds is normally achieved.
Other refinements in hatchery techniques, like the use of airlifts instead of aerating stones and better filtration systems, have contributed to make the whole operation more economical and especially more reliable, thus explaining the expansion of shrimp hatcheries in the last years.
In the long run, large hatchery systems could also be used as government seed banks to supply the required seed to the farmers and to ease conditions when wild seed would be scarce due to environmental problems in the nursery grounds. The largest hatchery known to this author, that of Marifarms Inc. in Florida, U.S.A., produced 375 million postlarvae in 1971 and 368 million in 1972 (Kittaka, 1977) enough to stock over 1 000 ha of ponds under intensive management, and between 5 000 and 10 000 ha under extensive of semi-intensive management. Hatcheries of this size are uncommon at present, but it is not unrealistic to think that they will become more abundant in the future.
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