Why We Shouldn’t Dam the Mekong

Zeb Hogan
Thursday, December 8, 2011

Biological Treasure Trove is World’s Most Productive River

Giant catfish
Giant catfish
Zeb Hogan

The Mekong River is still a relatively healthy, natural, free-flowing river. It is one of the most biodiverse rivers on Earth (in terms of freshwater fish). Most of its habitats and connections between habitats are still intact. Remarkably, the Mekong is still capable of producing 2.6 million tons of fish a year, despite fishing pressures from millions of people who depend on the river for sustenance. That makes it the most productive river in the world.

The Mekong is also home to many species of giant fish. It's unclear why so many species of giant fish occur in the 4,350-kilometer (2,700-mile) river, which runs from southern China to Vietnam. Certainly part of the answer is the river's size: Large rivers have more space and more food to accommodate larger fish.

Another part of the answer may lie in the productivity of the Mekong River Basin ecosystem, including the floodplains and flooded forests that provide an abundant source of food for many species of fish during the rainy season.

The hydropower dam planned on the Mekong River in Xayaburi Province, northern Laos, is a threat to the survival of the wild population of Mekong giant catfish. Under threat are the suspected spawning locations for many species of fish. The Xayaburi Dam is the first lower Mekong River mainstream dam to enter a critical stage of assessment. The four Mekong nations are expected to make a decision on the dam by January. The other dam closest to being approved is Don Sahong. The Sahong channel is the most important migratory pathway in Southern Laos.

One of the largest fish in the world, the Mekong giant catfish (Pangasianodon gigas) can reach 3 meters (10 feet) long and weigh up to 300 kgs (650 pounds). It is one of the most endangered fish in Southeast Asia. It is listed on the IUCN Red List of Threatened Species as Critically Endangered, and is listed on CITES and the Convention on Migratory Species. This is a culturally important and charismatic species. As a vulnerable Mekong endemic, the giant catfish symbolizes the ecological integrity of the Mekong River. Thus, the protection of this species is an important part in the sustainable management of the Mekong River Basin.

Almost all of the information that we have about this species – that the Mekong giant catfish is highly migratory, seems to need specific cues to spawn, cannot reproduce in reservoirs, and probably spawns in northern Thailand and in Laos – suggests that the Xayaburi Dam and other Mekong dams will have serious negative impacts.

The same is true of other species of Mekong giants: We know very little about the ecology of these species, but what we do know suggests that they need healthy, free-flowing rivers to survive.

Without further study, it's highly likely that mainstream dams will drive at least one, if not all, of these species to extinction. We've seen something similar happen on the Yangtze, where the two largest species are in grave danger after major dam construction (one, the Chinese paddlefish, may already be extinct).

Other threats to the Mekong’s megafish include over-harvest, habitat degradation (such as dredging and blasting upstream of the only known spawning ground of Mekong giant catfish), and invasive species. Up to 80% of Mekong giant fish are at risk of extinction.

Way Forward

There are several actions that would help ensure the survival of the giant fish species of the Mekong, including:

  • Maintaining connectivity between rearing grounds and spawning habitat. Many species of Mekong fish have complex life cycles that involve long-distance migrations. Maintenance of migratory pathways is crucial. Existing fish passage technologies cannot handle the massive volume of fish migrations, which can reach up to three million fish per hour at peak migration times.
  • Healthy flows for a healthy, productive river.  Both the fish and the fisherfolk of the Mekong are adapted to the natural cycle of dry season/rainy season. Flows often cue fish to migrate or spawn and the high flows of the rainy season open up vast habitats for feeding fish. Likewise, local people have invented all manner of ingenious ways of catching fish, and most of these methods are adapted to a specific site, flow, and time of year. If dam projects proceed, it will be critical to design dams in concert with an environmental flows management plan that allows for the most natural river flows possible. Implementation of such a plan will need upfront funding and long-term commitments.
  • Regulation and monitoring of harvest. Over-harvest is a serious threat to the Mekong's largest, longest-lived, and most vulnerable species. Mekong giant catfish, "dog-eating" catfish, and giant barb (Catlocarpio siamensis) are extremely rare, with only 5-10 adult fish caught per year. In areas with heavy fishing pressure (and that includes virtually the entire Mekong Basin), catch of the largest fish must be regulated to ensure their survival. Lessons from other parts of the world indicate that relatively slow-growing large-bodied fish cannot sustain heavy fishing pressure indefinitely.
  • Research and decision-making based on research: Research on the ecology and conservation status of giant fish is urgently needed in the Mekong River Basin. The "dog-eating" catfish is a case in point. We know almost nothing about it and yet it is undoubtedly one of the largest, rarest, and most vulnerable fish in Southeast Asia. It’s likely that at least 100 times more research is being done on salmon in the US Pacific Northwest than on fish in the Mekong, but the consequences of losing the Mekong’s fish are 100 times more significant in terms of biodiversity and potential impact to livelihoods.

Zeb Hogan is an assistant professor in the Department of Natural Resources and Environmental Science at the University of Nevada. He leads the Megafishes project (megafishes.org), an effort to protect the world's largest freshwater fishes.