What is threatening Mekong Delta fisheries?
Recent data and reports show the richest inland fishery in the world, situated in the Mekong Delta in Southeast Asia, is under serious threat from the twin effects of global warming and the more direct actions of man on the landscape. In the longer term, if these conditions continue, major export species could be affected.
An unusual drought from mid-May has reduced water levels in the upper section of the Mekong River to record lows. As a result, sea water is encroaching from the south caused by the annual tide, which this year is pushing further up the river and bringing in more seawater than normal – salt water has been found 60 km (37.3 miles) inland according to a report by the BBC World Service in Vietnam. The highest salinity is likely to be reached in March 2016, with the level beating the previous record set in the dry season of 2005.
In addition, a proliferation of hydropower dams in the north and large-scale sand mining are endangering the delta. As a result of these changes, an alarming 500 hectares (5 sq km) of land are being lost to soil erosion every year.
The Mekong Delta, where the mighty Mekong River splits into literally thousands of channels and small waterways, covers areas of Cambodia, Laos, Thailand and Vietnam. It houses an extremely rich inland fishery where hundreds of species are caught. The Tonle Sap to the north of the Mekong Delta in Cambodia is also being affected and the livelihoods of thousands of fishermen are in jeopardy. Tonle Sap is one of the biggest freshwater fisheries lakes in the world where catches make up about 60 percent of Cambodia’s total inland haul.
World Bank figures put the total catch at 138,600 metric tons (MT) in 1995, though more recently the Mekong River Commission (MRC), an intergovernmental body, has estimated the catch at between 177,000 and 252,000 MT.
It is not just freshwater fisheries which are being affected. Saltwater intrusion destroyed more than 6,000 hectares (60 sq km) of rice fields last year. Ironically this devastation could be of benefit for seafood export markets as many rice farmers are turning to saltwater shrimp farming, mostly the white legged shrimp, Penaeus vannamei.
In the north, the building of hydropower dams is causing the most concern. China has already built six “mega dams” on the Mekong River and is planning another 14 during the next decade. Dam construction on the upper Mekong has already had an impact downstream, especially along the Thai-Lao border where communities have suffered declining fisheries and changing water levels that are seriously affecting their livelihoods.
Meanwhile Laos, Cambodia, Thailand and Vietnam are planning to build a dozen more dams on the lower Mekong, thus blocking fish migration and affecting the river’s ecology. There is also evidence that new dams retain vital nutrient-rich sediments which replenish the river bed and on which marine life depends.
There is a third disturbing development in that tens of millions of cubic meters a year of sand are being mined from the lower Mekong River. The dredging is to allow big ships to enter smaller tributaries and canals but the waves they cause break embankments and flood homes.
The Intergovernmental Panel on Climate Change has long warned that the Mekong Delta will feel the effects of climate change. Unfortunately the countries in this region are embroiled in dam development disputes and are not working together to adapt to the new conditions.
The crucial question as far as export markets are concerned is what will happen with shrimp and fish farming operations in the Mekong if these environmental changes continue.
The extensive shrimp farming operation already written about (see SeafoodSource 1 September) where shrimp are put out in flooded rice fields is a first step toward solving a potential freshwater shortage.
The situation for pangasius is different in that the fish can live in brackish water and is not so dependent on freshwater. But in the long run there will be also problems if the salinity continues to rise and water levels to shrink.