Field Notes Tonle Sap Lake

Stimson Southeast Asia program director Brian Eyler recently visited Plov Tuok, a community of 800 floating homes atop of Cambodia’s Tonle Sap Lake — the largest lake in Southeast Asia and the world's largest inland fishery. The visit was facilitated by the International Union for the Conservation of Nature (IUCN), and Brian witnessed first-hand the progress of fish conservation zones that were established by local villagers and IUCN in 2014.

These are his field notes.

The Tonle Sap is the world’s largest inland fishery with more than 350,000 tons of fish harvested from the lake each year...

To put this into perspective, the yearly catch is more than double what comes out of all of North America’s rivers combined. Each year Cambodians consume an average of 75kg of wild caught fish, making fish the top contributor of protein to Cambodian’s diets. This also makes the entire population reliant on the future of the Tonle Sap’s fish production.

What isn’t consumed as fresh fish is processed by local communities into prahok, a pungent fermented fish paste that can be eaten throughout the year. Farmers travel from faraway provinces to exchange rice or cash for prahok. The seasonal gathering of communities and families to make prahok is a millennia old cross-cutting tie that binds social cohesion and reinforces local Khmer tradition.

The massive volume of fish produced by the Tonle Sap comes from the Mekong's flood cycle when each year, the river running out of the Tonle Sap into the Mekong mainstream reverses direction. During the monsoon season, so much water flows through the Mekong system that it causes the Tonle Sap to back up and expand five times its dry season size.

The lake's depth fluctuates between less than a meter in the dry season and nine meters at peak flood season. The yearly influx of water sends fish eggs and juveniles into the flooded areas to feast on a smorgasbord of organic matter not otherwise available during the dry season. This abundance of nutrient availability creates an explosion of the Tonle Sap's fish population.

To adjust to the lake’s seasonal rise, communities of Khmer fishermen build stilted homes close to the lake’s edge. Most go to the lake every morning to fish and check their traps. In the monsoon season, livestock and local gardens are raised on floating platforms.

The landscape looks entirely different in the dry season. Locals still fish on the lake, but some also plant cash crops like mung beans and cassava in nutrient rich fields exposed by the retreating floods.

More than 100,000 people live in these resource rich communities and their livelihoods depend on a successful fish harvest. But cash cropping pressures the locals into converting the flooded forest into farm fields and this threatens the provision of nutrients that supports the explosion of the fish population during the monsoon season.

Other communities like Plov Tuok live in floating homes on the lake. In the Khmer language, Plov Tuok means “the way the boats go” and over the years, the boat traffic drew outsiders to fish in the community’s waters. Historically, fishing on the Tonle Sap was managed by commercial firms with licenses for huge fishing lots.

This practice excluded locals from fishing and into the early oughts threatened to entirely deplete the lake of its fish. In 2012 Cambodia’s Prime Minister Hun Sen abolished the commercial lot system as a way to conserve the lake’s resources and designated the lake as a common fishing area for local residents.

However, a lack of foresight and planning created a free-for-all situation for local fishermen who further depleted the lake of fish...

In Plov Tuok, locals and outsiders targeted a deep pool in the dry season where fish were known to use as their habitat. They nearly succeeded in removing all the fish from the pool. For two years, annual fish catches were at all-time lows for the community and many considered leaving to find wage work in Phnom Penh.

In 2014, the European Union provided financial support to establish a 24 hectare fish conservation zone at Plov Tuok. The Fisheries Action Coalition Team, a local NGO, and IUCN worked with the local community to protect the deep pool and prevent outsiders from fishing there.

The IUCN team frequently engaged with community members who at first did not understand the conservation approach. A ranger team composed of community members monitored the zone day and night in boats during the dry season.

When the occasional violator was caught, the rangers would invite them for tea and explain the benefits of fish conservation. After a few seasons of successful monitoring, outsiders knew to avoid fishing in or near the zone. And then the fish came back. Even some endangered fish species like the Mekong Giant Barb are beginning to reappear according to a local who showed me a photo of a Giant Barb that he caught and released.

The zone’s creation also helped protect the community’s “Ghost Forest” a large patch of flooded forest used to bury the community’s deceased in the ground during the dry season or in coffins in trees during the monsoon season when the water was high.

Locals prioritized the forest as important cultural space and its inclusion in the conservation zone has prevented the forest from being cut down or picked over for timber. It is one of the few remaining intact forest spaces around the lake and is home to a variety of mammal, lizard, and bird species.

Today, Plov Tuok thrives.

The local commune chief told me, “The people are happy and they have the urge to protect fish. They are happy because the fish are abundant.”

Only a few of Plov Tuok’s youth have left to seek jobs elsewhere and the commune is abuzz with activity entirely conducted on the water. Success can be attributed to IUCN’s approach to build capacity within the local community, effective local leadership, and investment in physical infrastructure to mark the limits of the conservation zone.

IUCN has provided a small investment grant to the community which will provide funding over the next five years to maintain the conservation zone’s infrastructure and compensate locals to keep up patrols. Beyond that time frame however, the future of the conservation zone is uncertain.

My talks with community members also revealed concerns about how dams upstream of the Tonle Sap will impact the lake’s natural resources. Most were aware that dams could cut off the migratory pathway of the fish between the lake and breeding grounds upstream. But few understood how dams threatened the Tonle Sap’s annual reversal and flooding cycle.

Upstream mega-dams in China have a regulatory effect on the river's hydrology, delivering more water in the dry season and less water in the monsoon season. But thousands of communities along the Mekong and Tonle Sap lake rely and thrive on the provisions of the annual flood pulse and have adapted their livelihoods. Regulating water flow is a direct threat to their livelihood and the viability of the Tonle Sap's fishery.

Laos has plans to build more than 150 dams upstream of the Tonle Sap on the Mekong’s mainstream and tributaries and Cambodia has plans for dozens upstream.

This increase of river regulation will keep more water in the lake permanently and with less water flowing into the lake during the monsoon season, fewer nutrients will be available for the robust food web that makes this lake the world’s largest inland fishery.

Indeed, Plov Tuok community members confirmed that the lake in 2017 flooded earlier than usual and maintaining higher level longer than expected.

As I boarded the boat to leave Plov Tuok, a local man sent me away with words of assurance, “We’re not going to back down on this success. If we do nothing we will not succeed. If we do something then there will always be obstacles along the way.”

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Created with photos and videos by Brian Eyler, Google Earth, and Open Development Mekong

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