The Tonle Sap is “doomed”.
The ecosystem of the gigantic lake – whose annual flood cycle has been the pulse of Cambodia for millennia, and on which millions depend for food and irrigation – is set to spectacularly collapse, throwing into question everything from Cambodia’s food security, to its economy, to its demographics.
At least, that is, if drastic measures aren’t taken – and soon.
Such was the prevailing sentiment at the International Symposium on Flood pulse Ecosystems, where researchers convened last week in Siem Reap for a conference whose tone alternated between frustrated and funereal.
In more than a dozen interviews, Cambodian and international experts from a range of natural and social sciences studying the Mekong River, the Tonle Sap and the surrounding floodplain pointed to the already-visible effects of climate change, overfishing and dam construction on the indispensable ecosystem as cause for tremendous concern.
Acknowledging that changes have already been seen in annual rainfall and to the all-important “flood pulse” – the cyclical flooding of the Tonle Sap from the Mekong River that is crucial for fish production and floodplain agriculture – Environment Minister Say Sam Al pledged support for researchers and issued a call for solutions.
“The seasonal flood pulse cycle is very important. If we do not have that, then there would be a lot of problems,” he said, going on to ask the room: “How much change can the lake tolerate?”
The short answer, experts said, is not much.
University of South Florida Professor Mauricio Arias, a leading regional hydrologist who has studied the flood pulse for over a decade, said that dams built upstream along the Mekong River, as well as the effects of climate change, have irreversibly harmed the ecosystem.
“We talk about how climate change will affect, or how the dams will affect, but we’re already seeing those changes happening,” he said, adding that six hydropower dams already have left “strong signatures” on the flood pulse. Three dams are currently under construction in the Upper Mekong River, while 27 tributary dams are in the works in the lower basin.
“We’re going from a wild Mekong . . . to a closed river system that’s boring and dead [like the] Colorado River,” Arias said, referring to a river in the American West that was heavily dammed.
This will almost certainly have an effect on the productivity of Tonle Sap wetlands, which are dependent on the natural variation of the flood pulse. The lake’s fishery accounts for some 75 percent of the country’s protein production.
On top of the ecological threats, overfishing is already straining the country’s freshwater fisheries.
“The doubling of the population on the lower Mekong basin over the last 30 years has been a major driver of change,” said Ratha Chea, a freshwater ecologist and hydrologist at the University of Battambang.
As a result, he said, fishermen are working longer to bring in the same catch and travelling further from the lake shore.
“This could be a sign that the lake has reached its bearing capacity,” he said. Chea further noted that models predict a 70 percent drop in floodplain sedimentation by 2040, which would deprive fish of their principal nutrient source and drive down production.
Fish catch data collected over a 15-year period ending 2015 show that while production has remained steady in terms of total catch, the composition of that catch has changed dramatically.
More and more, fishermen’s nets are filled with a selection of small species of fish, while larger fish are becoming rarer, said Ngor Peng Bun, a Fisheries Administration officer and doctoral candidate at the University of Toulouse who analysed the data.
“This is not a good sign,” he said. “This is the sign of an unsustainable fishery.”
Kevin McCann, an ecologist from the University of Guelph, described the data as “frightening”. An expert in modelling ecosystems, McCann said that the changes in the fish population indicate that nature’s ability to respond to heavy fishing has reached its limit.
“Within that, if you even look at the fast growing things, they’ve been getting truncated . . . That’s the last straw before the system can’t respond anymore,” he said.
Evan Fraser, a food security researcher from the University of Guelph, said that the likely consequence of maintaining the status quo – while adding more dams and suffering droughts in the region – could be a “precipitous” decline in the fisheries.
Fraser’s research on how communities may respond to declining fish production shows that in the absence of a policy that gives them something else to do they will initially just fish more aggressively. But as catches get poorer, Fraser continued, people will move away, contributing to already existing concerns about migration.
Chris Jacobson, a researcher from Australia’s University of the Sunshine Coast, who spent 2015 and 2016 conducting fieldwork on migration in collaboration with the UNFAO, the Environment Ministry and the University of Battambang, sees financial hardship ahead for floodplain farming communities.
She found that in four communes in three provinces around the lake climate change was driving half of all migration. Migration had also affected half of all households, she found, and among land-owning farming families, nearly one-quarter had at least one family member migrating due at least in part to climate change.
On top of that, she said, only half the time did sending a family member away from the countryside to generate income actually help feed more mouths, with food insecurity peaking at around 60 percent for migrant households and at 45 percent for nonmigrant households in September when rice is planted.
“We don’t know whether those communities have the resources to make that switch or are stuck in a poverty trap,” she said. Such concerns raise questions about what will happen should those who rely on the water switch to agriculture.
For Jacobson, there’s a crucial need for more information about how to address loss of livelihood due to environmental changes before a policy solution can be devised.
While many farmers around the lake are already migrating for economic survival – largely to Thailand or Phnom Penh, according to Jacobson – livelihood changes among fishermen could lead to “social upheaval”, which could potentially make food insecurity worse.
For Fraser, there’s no shortage of precedents to look at when it comes to a rural-to-urban migration motivated by ecological factors.
“We’ve got lots of historical examples: the drought in Syria that brought people into the city, the drought in Rwanda in the 1990’s that is now seen as one of the catalysts for the Rwandan genocide,” he said.
“Going back even further you’ve got the French Revolution that began as El Niño-induced droughts that pushed people out of the countryside and into the streets of Paris. Typically history tells us that when this dynamic happens people start taking to the streets in the cities, protesting political corruption and a lack of services, poor infrastructure, imbalanced power, and poor economics.”
Environment Minister Say Sam Al acknowledged the security concerns about social disruption, saying a scientific assessment is needed.
“We will be committing funding to research [locally],” he said, adding that funding would come through on a case-by-case basis and that the ministry will also seek to improve research facilities at universities throughout the Kingdom.
While the prognosis was dour among many experts, they also noted that it is not too late for government to act decisively to manage the changes.
For Mauricio Arias, the professor, investment needs to be made to develop forecasting tools to anticipate changes better.
“We need to know if a massive fire is going to happen ahead of time . . . and forecast on a seasonal basis what will be happening with the water, the landscape and the fish production,” he said.
According to Vittoria Elliot, the Mekong science director for Conservation International, the ability to implement policy exists, but solutions – for now theoretical – urgently need to be tested.
She said there’s “still hope” for the fisheries, but sees the window of time to act as no more than three years – in 2020 a hiatus on building new dams is lifted. She predicted the planned 2,600-megawatt Sambor dam in Kratie province would be the final straw for the country’s fisheries if it is built.
“When you stick the Sambor dam in, then there’s no point in any of us talking about developing community fisheries,” she said.
For Ratha Seng, a socio-economist at the University of Battambang who studies community fisheries, government reform is also needed.
“We [the scientific community] want to solve the problem, but we cannot do anything without the participation of the government,” he said, adding “we have quite a few science results but translating them into something that will help make policy decisions is the next challenge”.
“We’re at the tipping point.”
NOTE: This article has been updated to reflect revised figures from Ratha Chea, a freshwater ecologist and hydrologist at the University of Battambang, on the future productivity of the Tonle Sap Lake.