they may escape into nature and establish viable populations that compete with natural ones, or that they will cross-breed with specimen from natural populations, thus diminishing genetic diversity. Thus, hybrid cultivation in Amazonian fish culture requires intensive research aimed at avoiding these problems, e.g., by the produc- tion of mono-sex hybrids or triploids.
It may be argued that fish culture on a major scale is economically not viable, as long as there is productive fishery for the same species. However, stocks of highly valuable species are, at least regionally, over-fished and prices are increasing; in addition, fish production is highly seasonal, which leads periodically to low supplies.
Fishery is concentrated mainly along the large whitewater rivers whereas new urban centers develop along the new highways, far away from the landing sites of fishing vessels. Here, fish culture has the advantage of low transport costs from producer to consumer.
Today, fish culture in Amazonia remains a complementary activity to fishery, providing high-quality fish at reasonable prices during the entire year. Over the long run, some species, such as tambaqui, pirarucu, and large catfish, have export potential, but this requires large-scale production at low cost throughout the year.
This can, however, be achieved, as shown by Vietnam, which in two decades established a catfish (Pangasius pangasius) culture industry whose current annual production is more than 1 million tons, with a considerable portion being exported. The várzea plays a minor role in fish culture not only because of direct competition with regional fishery but also because of fluctuations in the water level of large bodies of water, which create serious technological problems.
Nonetheless, the availability of cheap fish as food for highly prized carnivorous species, such as pirarucu and large catfish, may provide opportunities in specially adapted lakes.
The major problems of agriculture in the várzea can be summarized as follows.
1. The period of plantation and harvesting is determined by the hydrological cycle, which is not in synchrony with the natural plantation cycle. The highest water level is reached about 3 weeks after the beginning of the dry season. Since the growth period of crops coincides with the dry season, when there is a water defi- cit in the soils, expensive irrigation is required for many crops.
2. When the river rises quickly, farmers may lose a portion of their crops.
3. Very high floods can lead to the loss of those perennial crops that are scarcely flood tolerant and are therefore planted on the highest levees, such as bananas, manioc, and papaya.
4. The concentration of production to within a specific period may result in an excess of products at the market and thus to a decrease in prices.
5. Várzea soils are very heterogeneous in structure because of small-scale changes in the sedimentation pattern. This limits the potential level of mechanization and the establishment of large monocultures.
6. There are severe deficits in infrastructure, such as transport, schools, hospitals, and a reliable supply of electricity.
7. There are periods of heavy insect molestation, e.g., mosquitoes, and horseflies, lead to extensive losses.
An economic analysis of the agrarian production systems of the várzea identified two different approaches. Traditional systems are low-profit subsistence systems in which diversified production minimizes the risks. These systems still contain many elements of the “caboclo culture,” considered by Parker (1989) to be a biological, cultural, and historical link to the floodplain Indians of post-contact Amazonia.
Such elements are, for instance, the maintenance of species-diverse home-gardens and the practice of mutual aid systems, such as the preparation of cassava flour, the clearing of new land for farming, large-scale fishing and hunting operations, the construction and maintenance of community infrastructure, and mutual assistance in the case of diseases, accidents, travel, etc. (Noda et al. 2000).
Modern systems are labor-intensive and specialized, produce for local markets and compensate higher risks with higher profits, as shown in Table 23.2. Mutual aid is substituted by the regular payment of farm workers. Specialization directed at vege- table and fruit production is associated with the highest labor and land productivity, but the products are perishable. Production is feasible only near urban centers and the losses are high. During the last several years, efforts have been made to overcome the periodicity of the productive cycle. One such approach to maintain production during the high-water season is the planting of vegetables on the highest levees in wooden cages mounted on posts, to protect the crops from flooding. These efforts should be assisted by the government with on-farm research to overcome technical problems because: (1) even on small plots the várzea can sustainably produce enough to meet a considerable part of the local demand for fruit and vegetables and (2) they allows many people to remain in rural areas, because of the high demand for labor, rather than migrate to the over-crowded cities. Furthermore, well-targeted marketing cam- paigns can be used to revive interest in several local high-quality products that have
disappeared from the market because of low acceptance, such as taioba (Colocasia sp.) and ariá (Calathea allouia) (Bueno et al. 2000). These products can be reintroduced in the food offered not only to local people but also to tourists.
An over-reliance on specific crops can negatively affect biodiversity in the várzea.
For example, in the middle of the last century, large areas were deforested for the cultivation of the fiber crops jute (Corchorus capsularis L. [Tiliaceae]) and, to a lesser extent, mallow (Urena lobata L. [Malvaceae]) (Homma 1998). When the boom
Table 23.2 Comparison of the land and labor productivity associated with different production systems of the central Amazonian várzea (Modified from Junk et al. 2000b)
Land
productivity Labor
productiviy Gross farm income US$ ha–1 US$ man–1 day–1 US$ year–1 Arable farminga
Staple-crop farming 424 2.32 1,781
Vegetable farming: Low income 468 2.24 1,639
(mixed farming) Medium income 883 4.59 3,890
High income 1,130 7.62 6,890
Vegetables
(intensive) Tomatoes 1,680 16.80
Cucumber 1,300 12.20
Lettuce 3,050 19.20
Fruits
Papaya 1,896 8.50
Passionfruit 1,846 8.00
Banana 916 8.00
Other field crops
Watermelon 430 16.00
Jute 480 1.80
Animal farminga Cattle-ranching
(extensive) Beef 33.8 4.90
Cheese 30.6 5.56
(intensive) Milk 59.7 6.97
Water-buffalo ranching
(extensive) Meat 32.9 11.25
Forestryc
Selective logging 15 – 57e
Forest culturec 79 – 237e
Fisheryd
Actual 338
Potential 675
a Junk et al. 2000b
b Gutjahr 1996
c Details in Table 23.3
d Theoretical production of comestible fish 90 g m–2 year–1 (Bayley 1983) with a market value of US$ 1 kg–1; present use: 50% (Junk et al. 2000b). Cost for fishing effort: 25%.
e Based on an exchange rate of 1 US$ = 1.80 BR$
T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T
ended, in the 1980s, these areas were abandoned and subsequently became colonized first by large perennial grasses (Echinochloa polystachya, Paspalum fasciculatum) and later by a species-poor secondary forest that today represents the main forest cover of the lower Amazon várzea. This experience supports the need to protect at least part of the várzea alta because of its importance for biodiversity (see below).