Dams over troubled waters

VietNamNet Bridge 28 May 2011 

Much has been said about the impacts of dams on freshwater fish stocks in the Mekong River. However, the effects on marine fishery output also deserve thorough consideration.

The Mekong Delta boasts Vietnam’s biggest marine fishery output although its coastline is only some 736km long, less than a quarter of Vietnam’s.

Figures from the General Statistics Office show that marine fishery output in the Mekong Delta hit 606,500 tons in 2009, almost equal to that of Vietnam’s southeastern region, central and northern central regions and the Red River Delta combined, and nearly eight times that of the Red River Delta (77,900 tons). The Mekong Delta had 25,000 fishing boats in 2008, including 6,000 off-shore vessels, and saw its fishery export jump from US$1.2 billion in 2003 to US$4.2 billion in 2009. In fact, its export destinations number more than 130 countries at present.

The fishing industry also fuels the growth of some other sectors such as processing, transport, commerce and material supply. It is thus no surprise why Kien Giang’s fishing ports are the biggest in Vietnam. The south’s abundant seafood output is ascribable mainly to nutrients supplied by the Mekong River.


The plume

The Mekong River basin extends far beyond its estuary to include a plume, whose seafood output depends on nutrients from the river. On average, the Mekong River discharges some 475 billion cubic meters of water per annum into the sea. The volumes discharged peak in October and hit their trough in May.

Together with climate change, pollution, overfishing and the decline of mangrove forests, hydropower dams have posed a threat to the Mekong Delta’s fishery output. The strategic environmental assessment (SEA) report compiled by the Mekong River Commission (MRC) contends that the primary biological productivity of nearby coastal areas will fall due to a nutrient supply crunch. Consequently, the fishing industry and supporting sectors will suffer.

The report states that the delta’s marine fishery hinges on approximately 16,000 tons of attached nutrients deposited by the Mekong plume in the shallow, near-coastal shelf of the region. The issue is to what extent marine fish stocks will be affected by current and upcoming hydropower dams.

Experience from the world

The detrimental effects of dams on marine fishery have been evident in many countries for a long time. A report by A.A. ALEEM published in Marine Biology and presented at a conference in September 1970 in Tokyo indicated that the construction of Aswan dam in Egypt and disruptions in the flow of the Nile River into the Mediterranean River since 1965 (35 billion cubic meters per annum) were deleterious to coastal areas in the region. Brackish-water fish stocks also dropped.

The nutrient content slid sharply, plankton virtually vanished and sardine catches plunged from 15,000 tons in 1964 to 4,600 tons in 1965 and 554 tons in 1966. As nutrients, organic substances and silt deposits shrank, biodiversity was adversely affected. Coastal erosion also accelerated, inflicting damage on reservoirs and leading to an urgent need for remedies.

Meanwhile, statistics from the Food and Agriculture Organization (FAO) show that Australia’s freshwater and marine fishery outputs in 2005-2007 reached about 140,000 tons per annum on average. According to the Australian Bureau of Agricultural and Resource Economics, the country’s marine fishery output dipped below 250,000 tons in 1997-2004.

These figures trail far behind the Mekong Delta’s although Australia has a coastline of 35,000km (only the continent is considered), nearly 50 times as long as that of the delta. In fact, Australia’s marine fishery output is approximately the same as Kien Giang Province’s (239,000 tons in 2000). This is ascribable to Australia’s vast deserts and low rainfall, which cause limited surface runoff and nutrients. As a result, Australian waters are not conducive to marine life.

Once hydropower dams along the Mekong River have all been inaugurated, the Mekong Delta risks facing the same problem, triggering a domino effect that leaves many sectors in tatters. Farmers, in particular, will be hit the hardest.


Research is vital

A growing consensus among scientists is that the dams are among factors that will reduce nutrient supply and fish catches in the Mekong River. The SEA report also forecasts that silt and nutrient supply to nearby coastal areas will fall by some 50-75% by 2030 and exert pernicious impacts on marine fishery output, as well as Vietnam’s fishing industry and related sectors, which have clocked up blistering growth over the past decade.

The report admits that scientists have only a tenuous grasp of the Mekong River’s marine fishery potential even though its seafood catches have surpassed 500,000 tons per annum. It is added that when the impacts have been clearer, estimated losses are likely to be enormous.


Unlike in the case of other important rivers such as the Amazon, the Yangtze or the Mississippi, the plume of the Mekong River has not been the subject of extensive and intensive research. Socio-economic and environmental impacts on the Mekong Delta remain murky, making it hard to assess the transnational effects of hydropower dams on the Mekong River.

It is clear, however, that the Mekong Delta is prone to a growing array of disasters with grave environmental, economic and social implications. The damage that hydropower dams inflict upon the Mekong River’s marine fishery output and productivity will probably be irreparable and permanent. Research on the magnitude of such damage is therefore crucial, as is that on natural processes in coastal areas and at estuaries. This task entails efforts, time and money, and must be implemented as soon as possible.

Source: SGT