In terms of fish production, total world figures show an increase from 68.5 million tons in 1977 to 76.8 million tons in 1982 (Table 1) corresponding to an average annual growth rate of 2.3 percent. These nominal catch values include the sum for capture fisheries plus aquaculture since aquaculture yields are not distinguished in the primary data. However, these totals consist of three main components, each of which shows different trends. The first, and most important component, is capture fisheries for direct human consumption, the second is capture fisheries production for reduction to fish meals and oils, and the third is aquaculture.
Capture fisheries for direct human consumption did not show any significant increase in this period of time. Of the 8.3 million ton increase in total world production between 1977 and 1982, 5.6 million tons was due to catches of sardines, anchovies and similar pelagic species which, to a great extent, are used for reduction to fishmeal and oils. A study carried out in 1981 (FAO, 1982) indicated that of the demersal fish catches, one third was reduced to fishmeal in addition to about 40 percent of the small pelagic species. The ratio of fish for food to fish for reduction to fishmeal and oils has fluctuated from about 2 to 2.5:1 in recent years, suggesting that some of the fish which were used for reduction in the past are now being consumed directly as human food, to meet the increased demand (see Table 2). It is also worth noting that by 1981 aquaculture production represented 14 percent (7.4 million tons) of the total fish and shellfish resources for direct human consumption.
More recently, preliminary estimates of aquaculture production, collected through questionnaires by the Aquaculture Development and Coordination Programme (ADCP) of FAO in 1984 and by the authors, show a considerable increase in total production for the years 1982–83, reaching amounts in the range of 8.9 to 10.5 million tons, suggesting a considerable increase in the aquaculture share of fish production for direct human consumption.
Fish and shellfish are an important component in the daily animal protein supply of third world populations. The proportion in the developing world averages 20.7 percent of the total daily animal protein supply (including meat and offals, eggs, fish and seafood, and milk and derivates), with values ranging from 9.4 percent for Latin America to 31.3 pthe Far East (see Table 3). Taking into consideration the inability of capture fisheries to meet the total demand for fish and shellfish products, in particular in the developing world where population growth rates are high and fish and shellfish are major protein sources in the diets, it is clear that aquaculture is likely to have a more important role in the future. This trend is already reflected in national development programmes of many developing countries as well as in those of the financing community.
In the case of brackishwater aquaculture the most important organisms for the subject of this paper are tropical species of penaeid shrimps and finfish, including milkfish and mullets. Brackishwater aquaculture has developed over the last three or four centuries to include at present a total area of several hundred thousand hectares, mainly in Southeast Asia. Modern and technically complicated production in coastal ponds dates, however, only from the beginning of the 1960's. The dominant product of coastal brackishwater ponds in Southeast Asia has been milkfish, Chanos chanos, with shrimps representing a welcome secondary yield from the same ponds. The total surface areas used for brackishwater ponds are very large in Indonesia and the Philippines, (205,000 and 196,000 ha, respectively) and much smaller in Thailand, Burma and Malaysia (32,000, 4,000 and 1,200 ha, respectively).
Estuarine and coastal marine environments are often very productive biological systems, having an abundant supply of nutrients such as phosphate and nitrate to stimulate primary production by phytoplankton and macrophytes, as well as substantial inputs of organic detritus from land. Shallow marine waters generally also have abundant oxygen derived by exchange of dissolved gases with the atmosphere, and are well buffered against changes in acidity by the presence of appreciable dissolved carbonate and bicarbonate ions. The basic concept of using pond systems fed by such productive coastal waters, partially diluted by natural freshwater runoff, to enhance the yield of desirable culture organisms, is clearly sound. By excluding predators, stimulating primary production with inorganic and organic nutrients, (and in some cases adding prepared feeds), it is feasible to obtain yields of culture organisms per unit area of ponds far above that possible with capture fisheries in coastal waters. With hatchery-derived larvae to increase stocking densities and the ability to control the size and timing of culture organism harvests, it is possible to maximize the economic returns based on market conditions. Yields up to 2.5 t/ha/yr for a variety of fresh and brackishwater species have been obtained in large areas of ponds in China (including Taiwan), as well as elsewhere, using semi-intensive management practices, i.e., by using the natural productivity of the pond enhanced by fertilization and with some supplementary feeding. 1
During the last two decades biologists working in aquaculture have emphasized a number of aspects of artificial reproduction of fish and shellfish. This research resulted in techniques that have freed the industry from dependency on natural reproductive cycles, which, in most cases resulted in marked seasonalities in the supply of seed to stock the ponds. Unfortunately not all species have proven to be relatively easy to breed in captivity and mullets and especially milkfish are amongst these difficult ones. On the other hand, hatcheries for mass production of shrimp fry are now a reality and all the main commercially interesting species of penaeid shrimps can be artifically reproduced, although with varying degrees of success.
These changes have led to a situation in which, due to the availability of more complete technology for production of shrimps, the limited and erratic supply of milkfish fry, and the high market price for the shrimps compared with that for milkfish, more and more producers are switching from milkfish to shrimp culture or at least are incorporating shrimps in polyculture with milkfish in the ponds.
These trends have been reinforced by the inability of world capture fisheries to meet the demand for shrimps on international markets; most of the shrimp fishing grounds are either near their maximum levels of exploitation or showing signs of overexploitation. Shrimp landings have stagnated at around 1.7 million tons/year for several years and it is the opinion of many experts that this level is not likely to be appreciably increased.
Shrimp production from aquaculture represents only a minor fraction of the world aquaculture production (in weight) but its growth rate during recent years has been much higher than that of finfish, mollusc or seaweed culture. Estimates obtained through questionnaires indicate that from around 71,000 t for the years 1979–80, annual crustacean aquacultural production had reached 123,000 t by 1982–83 indicating an annual growth rate of 18 percent. Of these 123,000 t, over 110,000 t of production were penaeid shrimps.
With the exception of Ecuador, which produced about 23,000 tons (heads-on) of brackishwater prawns in 1982, this type of aquaculture is dominated by Asian countries. Indonesia (30,600 t in 1982), India (between 10 and 15,000 t in 1984), Thailand (between 11,500 and 15,000 t in 1983), Taiwan, province of China (20,000 t in 1984), China (8,000 t in 1983) and Bangladesh (5,000 t in 1984) were responsible for about 75 percent of world brackishwater aquaculture prawn production. Other countries with estimated aquaculture prawn annual production in excess of 100 t were: the Philippines (3,000 t in 1982), Japan (2,000 t in 1982), Panama (1,700 t in 1984), Peru (1,030 t in 1983), Malaysia (500 t in 1984), Honduras (350 t in 1984), Brazil (160 t in 1984) and Colombia (around 100 t in 1984). Small amounts were also produced in Vietnam, Singapore, Korea, U.S.A., Guatemala, Martinique, Mexico, Bahamas and Antingua.
Brackishwater shrimp aquaculture production currently yields about 7 percent of the total annual shrimp landings of 1.7 million t, and thus contributes a minor, but growing segment of the total harvest of shrimps. Almost 70 percent of shrimp total landings are made by Asian countries (Table 4), with North American countries accounting for 15–20 percent, South America and Europe each about 5–10 percent, and Africa a minor contributor («5 percent). The ten largest exporters of tropical shrimp in 1981 were: India, Mexico, Indonesia, China, Thailand, Malaysia, Taiwan, province of China, Ecuador and Australia (Table 5). Although annual shrimp landings in excess of 15,000 t are achieved by a relatively large number of countries (20), the world imports of shrimp are dominated by a much smaller number of countries, with two countries (Japan and U.S.A.) accounting for almost two thirds of the total import market (Table 6). Together, Japan, U.S.A. and Western Europe completely dominate the world shrimp import market.
However, the three major import markets are served in quite different ways. Japan's imports consist mainly of raw headless shell-on frozen shrimps derived mainly from Asian countries (Hempel and van Eys, 1985) with India and Indonesia as the major suppliers. The U.S.A. market prefers white shrimps, which come mainly from South and Central America, but almost one half of its supply is from domestic landings. Cultured white shrimp from Latin America are well accepted by this market. Europe consumes considerable quantities of coldwater shrimps, mainly in northern Europe, while southern Europe shows a preference for Mediterranean and tropical species, mainly in head-on form. African landings tend to be channelled into the European market. Significant exports of coldwater shrimp (around 80,000 t), primarily to European countries are supplied by Denmark, Greenland and Norway. The international shrimp market is obviously quite complex, and involves a substantial number of countries, but to a first approximation, the portion of the large demand of the richer temperate zone countries which is not met by domestic fisheries, is supplied by developing countries, especially in tropical and subtropical Asia and Latin America. Of the total world landings, at least 40 percent of the equivalent live weight enters the international market rather than being consumed by the country of landing. For the larger, more valuable warmwater penaeid landings, the proportion of the total catch which is exported is much larger. The wholesale market value of shrimp imports to the 15 leading markets (Int. Trade Centre, 1983) in 1981 was approximately US$ 3 billion, representing a major source of income to developing countries.
Over the past few decades a number of developing countries have invested heavily in shrimp trawlers as the international market for shrimp expanded, driven by the very high prices commanded by large tropical shrimp. For example, in the Philippines, the wholesale price at landing centres for penaeid shrimp during 1979 and 1980 was about US$ 8/kg, or from 5 to 15 times higher than nearly all of the other categories of the total of 60 species items reported, (SEAFDEC, 1982). Using an estimated total wholesale market value of US$ 3 billion for the 600,000 t of shrimp which entered the international market, the mean value in recent years has been approximately US$ 5/kg. As shrimp landings have levelled off under heavy fishing pressure and some of the stocks have been overfished, the market stimulus to invest in brackishwater aquaculture has obviously been very strong. Summaries of trends in the world market for shrimp almost all point to such aquaculture development as the key to future expansion or stabilization of shrimp production (Int. Trade Centre, 1983; SCSP, 1983; Branstetter, 1983; Hempel and van Eys, 1985).
