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Source of income: Tourists and locals travelling in a ferry and boat along the Tonle Sap river during the recent Visak Bochea day in Phnom Penh. — AFP Source of income: Tourists and locals travelling in a ferry and boat along the Tonle Sap river during the recent Visak Bochea day in Phnom Penh. — AFP

Phnom Penh - 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 Cambodia does not have that, then there would be a lot of problems, he said, adding “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 were already seeing those changes happening.

“The six hydropower dams have already 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 lakes fishery accounts for some 75% 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, noting that models already show a drop in fisheries production by as much as 70% by 2040 from current levels.

Fish catch data collected over a 15-year period and ending in 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.

Source: The Star Online | 2 August 2017

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