Future management strategies for riverine fisheries should be concerned not just with achieving or maintaining a certain level of production, but also with ensuring that the maximum number of fishing folk, traders and other support personnel make a reasonable living from the fish resource. If this goal is accepted, then decreases in catch per unit effort should be of concern to the manager even where total production goes up since such decreases are apt to be associated with lower net incomes and an increased incidence of poverty. Hence the biologist's concern with such measures as production and catch per unit effort need be linked with the social scientist's concern with value of the total catch and with value of the catch to the different categories of fishing folk for whom net income received is a more important index than size of catch.
Accelerated change within riverine ecosystems in the tropics has made their management increasingly difficult. Major changes relate not just to the water resources of the river basins but also to human communities, including communities of part-time and full-time fishing folk. Welcomme (1979) has produced a useful four stage framework for examining the modification of floodplain rivers. Not only does this framework illustrate the impacts that multipurpose river basin development has had on fisheries, but it also emphasizes that management solutions must make sense in terms of multiple and frequently conflicting uses of water resources. As for communities in which fishing is an important fulltime or parttime occupation (hereafter called fishing communities) we also use in this report a four stage framework to emphasize the dynamics involved within fishing communities
Welcomme's framework illustrates an accelerating historical sequence in which flood control measures and dam construction are transforming river systems. Even more dynamic is the transformation of traditional fisheries along those river systems. Thirty years ago, Welcomme's slightly modified river systems would have been primarily associated with traditional fisheries. This is no longer the case since the large majority of local and immigrant fishermen along tropical river systems are intensifying production in response to market demands. Throughout the tropics, such transformations are altering the nature of multispecies fish stocks on the one hand and reducing catch per unit effort on the other. What is badly needed now is a fifth stage when fishing communities work closely with governmental and other agencies to effectively manage fish resources in the interests not just of production but also of employment and improved living standards. It is hard to imagine such strategies working without strong local participation, on the one hand, and locally and governmentally enforced restricted access on the other.
A number of problems -- both local and exogenous -- threaten the continued viability of riverine fisheries. These factors include: (1) the over-exploitation of certain fish stocks by local commercial fishermen; (2) the further pressure placed on the capacity of fisheries by the immigration of outsiders and the encroachment of non-local fishermen; and (3) environmental modifications that reduce the productivity of fisheries resulting from (a) the construction of dams and irrigation canals; (b) the pollution of fisheries from both agricultural and industrial sources; and (c) the clearance of upper catchment basins and floodplain forests for agricultural, fuel wood and other purposes.
Welcomme summarizes the evidence on over-fishing for all types of riverine fisheries in the late 1970s by stating that “well-documented examples of overfishing at the [fish] community level are rare and when recorded are often traceable to environmental variables… or to other human interventions. However, heavy fishing [can hasten] the decline by making the fish stocks less resistant to changes arising from other sources… it may be concluded that the ability of fish communities in rivers to support heavy fishing is very good and that most systems are still exploited at a reasonable level. … However, certain individual stocks are vulnerable and may easily disappear. Furthermore environmental pressures, when added to fishing pressures, may cause a collapse in the fishery” (1979:225).
While there are still fewer well-documented cases of overfishing of fish stocks by artisanal fisherfolk, limited access management strategies, even where they exist, are of decreasing effectiveness in protecting fisheries resources. There are two reasons for this. The first relates to population increase within the fishing community, and an intensification of fishing effort because of more efficient gear and increasing exports of fish. The other relates to the arrival of increasing numbers of immigrant fishermen who are overwhelming local communities even where they use legal techniques and conform to local customs (and frequently they do neither). For reasons such as these, an increasing number of competent observers have suggested cases where a combination of local and immigrant commercial fishermen along tropical rivers are overexploiting fish stocks. While the nature of riverine fisheries makes it difficult to assess the validity of these statements, there is little doubt that catch per unit effort has decreased significantly along certain rivers as fishing effort has intensified. Examples include Zambia's Kafue River (Hayward, 1982); the Amazon (Goulding, 1981); and the Maracaibo of Columbia and Venezuela (Beckerman, 1983).
In the Amazon case, Goulding feels that recent declines are due primarily to the high intensity of fishing since the mid-1970s, though changes in water level may also be a significant factor. In the Maracaibo case, Beckerman is even more convinced that intensified production is responsible. There a local Indian group, the Bari, depend heavily on the bocachico (Prochiloidus reticulatus). Between 1970–72 and 1983 average weights have declined from about 330 grams to 150 grams. “Commercial fishing downstream is almost certainly responsible” (1983 written communication to the authors), though Beckerman also notes the dumping of outdated insecticide in the river as another factor. Though there is little evidence in either of these cases that the multispecies fishery as a whole is threatened, the evidence does suggest that the living standards of fishing communities are in jeopardy. Noting in 1977 a catch per unit effort of 26 kilograms of fish per day (which is close to Smith's late 1970s estimate of 23 kilograms elsewhere in the Amazon basin), Goulding concludes that “given the present economy of the Amazon fisheries, somewhere between 20 and 30 kilograms per man day fished is the minimum level at which the commercial fisheries can function economically.”
Welcomme's cautiously optimistic assessment of the status of riverine fisheries in the developing world probably underestimates the impact of recent heavy population movements into areas supporting riverine fisheries and the consequences of the expansion of highly commercialized fishermen into the traditional fisheries of subsistence or semi-commercial fishermen. The explosive growth of the Amazon fisheries during the late 1960s and early 1970s, for example, was primarily the result of the rapid increase in immigrant population from eastern Brazil that swelled the number of men looking to fishing as a way to earn a living in the Amazon. Elsewhere, as in the arid and semi-arid lands of Africa, people are turning to riverine fishing not so much to earn a living but to survive -- the upper reaches of the drought-stricken Niger being a case in point.
In Zambia, a growing number of people are moving into the fishing sector because of the difficulty of finding employment in urban areas and the “formal” sector of the economy. The number of fishermen exploiting the Kafue River fisheries, for example, has grown rapidly in recent years as “men without capital, including rural and urban school leavers, men leaving low wage jobs in town, off-season… cane cutters, and more experienced fishermen from the northern fisheries” move into the area in search of employment. Most work as crew members on boats owned by absentee entrepreneurs, many of them civil servants or technical workers in Lusaka who have turned to the informal fishing sector as a way to beat the high cost of living in urban areas (Hayward, 1981 :6–7).
Elsewhere, the livelihood of many small-scale artisanal fishermen exploiting local fisheries is being threatened by the encroachment of highly commercial fishermen from the outside who are moving or expanding their area of operation as yields begin to decline in over-worked fisheries. In the Amazon region, for example, Smith reports that some of the vessels in the huge Manaus fishing fleet journey as far as 1700 kilometers from their port in search of fish. In their efforts to make a profit they have begun to penetrate “lakes hitherto only fished by subsistence folk. Several clashes have occurred between commercial fishermen and inhabitants of lakes in the region. In 1971 several lives were lost in the Manaus area over disputes regarding fishing rights” (Smith, 1981:122).
Among the nonfishing interventions by humans that affect the viability of riverine fisheries, dam construction has perhaps been the most significant and the most widely publicized. Dams, such as those already in place on a number of major rivers in Africa and India, adversely affect downstream fisheries primarily by (1) altering the seasonal flood to which many species of fish and many fishing folk have adapted and (2) blocking the migratory route of such commercially valuable species as Hilsa ilisha in India.
The loss of floodplain area necessary for the feeding and breeding of many riverine fish species can significantly reduce the productivity of fisheries downstream from dams. Welcomme (1979) notes, for example, that the productivity of the Niger River below the Kainji dam fell by 50 percent in three years (1967–1969) after the construction of the dam reduced the duration and magnitude of the downstream flood.
The restriction of the migratory route of many fish species can also lead to a serious decline in the productivity of riverine fisheries. Though some dams have successfully employed “ladders” that allow fish to pass the dam, in general these have been a failure in tropical rivers. In Brazil, for instance, many of the “Piracema” species have almost disappeared from the Rio Grande and its tributaries in the state of San Paulo because of dams that block the migration path of the fish. Though there are no immediate plans to dam the Amazon River, proposed dams on tributary rivers could seriously disrupt the currently very productive Amazon fisheries (Smith, 1981:127–30).
While the reservoirs backed up behind dams may more than compensate for the loss of productivity downstream as is the case with the Volta (Ghana) and Aswan High (Egypt and the Sudan) dams, different communities of fishermen may be involved, with living standards seriously declining below the dam unless fishermen leave their homes and move elsewhere. In the Volta case, many Tongu fishermen were forced to move permanently from their communities on the lower Volta River to Lake Volta after dam closure in the early 1960s disrupted the downstream fisheries (Lawson, 1972). Furthermore the electricity generated through large-scale dams, and the increased irrigation that often occurs, speed urban-industrial and agricultural development which negatively impact upon riverine ecosystems through increased pollution.
Pollution of riverine fisheries both from industrial effluents and agricultural chemicals is a growing concern in developing areas of the world. In India, “domestic sewage and industrial wastes are perhaps the greatest menace to Indian riverine fisheries and modern agricultural practices are increasing the pollution by pesticides.” On the Hooghly river, for example, a branch of the River Ganga in West Bengal, a 92 kilometer stretch “receives over 252 million gallons daily of liquid wastes from about 161 factories comprising textile and cotton mills, tanneries, paper and pulp mills, jute mills, distilleries, etc., and storm water and domestic sewage from the towns and cities situated on either sides of the banks” (Jhingran and Tripathi, 1977:43).
While less heavily populated countries in the developing world do not suffer from the extreme pollution problems found in India, there is already cause for concern in many areas (Welcomme, 1979:243–246). Comte (1982), for example, discusses the increasing problems with industrial and agricultural pollutants in Lake Victoria and the adjacent river system of western Kenya. Though not extensively documented, there concern is growing about the impact of agricultural chemicals, especially insecticides, that can easily contaminate nearby water sources, especially in areas using irrigation. Both industrial and agricultural pollutants tend to affect many different species of fish, killing some outright, reducing the growth rate or increasing the susceptibility to disease of others. Overall, pollutants in riverine fisheries result in a reduction in species diversity and a shift toward relatively smaller and shorter-lived fish (Welcomme, 1979:243–246).
Another environmental threat to the continued productivity of riverine fisheries is the clearance of the floodplain forests that are so critical to the ecology of many fish species. Both Goulding (1980 and 1981) and Smith (1981) warn that plans to develop forested floodplain areas for agricultural and livestock development schemes in the Amazon region will have adverse consequences for the many fish species that spend at least a portion of their life cycle feeding on the fruits of trees and other vegetation in the flooded forests. And it will have adverse effects on the many people dependent on those fish for a relatively low priced source of protein (Goulding estimates that “the food chain leading to about 75 percent of the total commercial catch originates in flooded forests, ” 1980:253).
The threat to the productivity of Amazon fisheries has already been realized in the Mekong - Grand Lac fisheries of Cambodia. Hickling has argued that the widespread clearance of floodplain forest for agricultural purposes was at least in part responsible for the decline in the yields of the Mekong - Grand Lac fisheries from 61,000 tons to 28,200 tons in the mid-1950s. He noted that by 1955 there was “greatly increased clearance of the flood forest for agriculture, which not only destroys a part of the source of food for the fish, but leads to erosion and, by deposition of the eroded soils in lakes and lagoons, is tending to fill them up. Both factors must be adverse to the fishery” (Hickling, 1961:143).
Increased deforestation in the upper catchment basins of many tropical rivers is also having an adverse effect on water quality through increased siltation and alteration of river regimes with increased runoff during the rains and reduced flow during dryer periods. Though of less significance than agriculture in the large majority of cases, fisherfolk contribute to the problem when they cut or purchase wood for smoke drying fish.
