The waters of the Mekong River and its tributaries have yielded a significant proportion of the protein consumed by the inhabitants of the countries through which it flows. While capture fisheries have contributed the bulk of production traditional fish farming has drawn on wild fry spawned by the diverse species of the Mekong River basin. Thus aquaculture was closely tied to the same fish stocks exploited by the fisherfolk of the lower Mekong Basin.
Reliable statistics of fisheries production in the basin are sorely lacking. Many estimates are no more than educated guesses. The large undocumented subsistence fishery contributes to the uncertainty. The Mekong River Committee has compiled current estimates and projected future demand based on fish consumption surveys (MRC 1992). Current landings are estimated at 868,000 tonnes. The inland fish production of 620,000 tonnes represents 71% of the total, the remainder being coastal capture and brackishwater aquaculture. Freshwater aquaculture produces around 27,400 tonnes, or 4.4% of inland fisheries production. It should be noted that figures for freshwater aquaculture in Viet Nam were not available for inclusion in the estimates.
There is no historical regional catch data which would indicate trends in landings. Anecdotal evidence seems to point to stagnation or decline, as in Lao PDR.
Per capita fish consumption in the four countries of the basin ranges from 30 kg in Viet Nam to 6.5 in Lao PDR, the lowest (MCR 1992). Estimated fish consumption for Laos should be treated with caution. It is derived from the estimated fish production and population. However, the estimated fish production for the country is probably seriously underestimated. Singh (1990) figured production from wetlands in Laos at only 38 tons, whereas Claridge (1996) maintains it should be on the order of thousands of tonnes. Claridge bases his comments on similar fisheries in Sumatra and the high consumption of fish by rural inhabitants in Lao PDR.
Projected demand is based on the assumption that 50% of animal protein requirements will be met by fish consumption. In this scenario, the minimum required production for the actual population of Lao PDR was 91,000 tonnes in 1990, or 3.4 times the estimated production. In the year 2000, this rises to 112,000 tonnes, or 4.2 times 1990 production. By 2025, this minimum requirement will have risen to 177,000 tonnes, nearly 7 times the 1990 catch (MRC 1992). In the face of declining or stagnant capture fisheries, aquaculture production will have to increase significantly if the population's minimum protein requirements are to be fulfilled.
Sustained production from capture fisheries in the lower Mekong basin faces growing challenges from several quarters. In addition to overfishing, major threats to fish production in the lower Mekong basin arise from deforestation, dams and industrialization.
As population increases, pressure on fishery resources will inevitably rise apace with the rising population. Both national and regionally coordinated management plans will be essential to insure sustainable catches. The existing data base is woefully inadequate for management purposes, but hopefully within the framework of the Mekong River Commission, this situation will improve.
Destructive fishing practices appear widespread, but their impact is unknown. Poisoning is common on tributaries of the Mekong. Small mesh gill nets and fishing on spawning grounds are also leading to resource depletion.
Upland degradation has severe effects on fisheries. Siltation interferes with spawning and migration, as well as eventually filling small reservoirs and wetlands. Acid runoff upsets primary production on which fish stocks depend and may be toxic in extreme cases. Fish kills have been noted during episodes of excessive runoff and accompanying high sediment loading.
The major cause of deforestation in Lao PDR is swidden agriculture, although industrial logging may become a more serious threat in the future as timber companies look for new sources of raw material. About 47% of the country retains its forest cover, but the annual rate of deforestation is 0.9%, of which only 0.1% is due to logging (RAPA 1996). The Lao government is trying to address this problem through controlled expansion of permanent paddy cultivation, the introduction of sedentary cropping systems on sloping lands, agroforestry development and supporting social development work.
Dams, actual and contemplated, along the course of the Mekong and its tributaries present a serious threat to fisheries, but on the other hand create opportunities to develop reservoir fisheries and aquaculture, partially compensating for the lost production.
Dams negatively impact fisheries in two major ways: they eliminate wetlands and block migration routes. Wetlands are crucial for the spawning and juvenile production of many species of Mekong fishes. They also serve as productive fishing grounds, particularly as waters recede during the dry monsoon. Dams block fish migration to spawning and feeding areas. Without adequate passageways for migratory species, entire fisheries are likely to disappear. While fishways are possible, little is known of the migratory behavior of most of the fish inhabiting the Mekong and its tributaries. Detailed knowledge of migratory behavior is required to design effective fish passages. Even so, the diversity of migrating species and their associated behavior may render fishways ineffective.
Some of the lost production can be made up by development of reservoir fisheries and aquaculture. Stocking of reservoirs with economically valuable species has been successful. Promising cage culture trials have been undertaken in Lao PDR. Fisheries in some reservoirs have increased landings, but the value of the fisheries may decline as fish populations shift from high value predators to low value small sized plankton feeders of the herring family.
Given the low level of industrialization in the Lower Mekong Basin, industrial pollution would not seem to pose much of a threat to fisheries. This could change with the increased mining and associated toxic runoff.
Gravel dredging in the main river channel may have deleterious effects on fisheries, but no studies have been done in Lao PDR to ascertain what effect, if any, this activity might have on fisheries.
