LINES OF THOUGHT ACROSS SOUTHEAST ASIA

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Conservation

Cambodia’s Tonle Sap Lake receives a record fish release

Mekong giant catfish were among the threatened species freed in Southeast Asia’s largest lake to counter persistent threats

March 24, 2022
Cambodia’s Tonle Sap Lake receives a record fish release
A fish attempts to escape the net of Ros Narin, an officer at the Freshwater Aquaculture Research and Development Centre in Prey Veng Province

The gulping fish stopped wriggling once Samol Chhuoy lowered it into the motionless waters of Tonle Sap Lake, causing the reflection of the Mekong giant barb to ripple.

“Bye-bye. Good luck,” said Chhuoy, a Ph.D. student with Wonders of the Mekong, as he released the giant barb, Cambodia’s national fish, into Southeast Asia’s largest freshwater lake.

The last part to disappear into turbidity was the fish’s dorsal fin and an attached lime-green tag – labelled 3415 – with a Khmer-language note instructing fishermen to take the captured fish to local authorities for a cash reward.

Tag number 3415 was one of nearly 1,600 threatened fish – representing three species – poured into the lake as part of the largest single release by Wonders of the Mekong, a research project funded by the U.S. Agency for International Development.

Researchers hope the captive-raised fish, including a 5-foot-long, critically endangered Mekong giant catfish, will bolster wild populations.

Video produced by Anton L. Delgado

“We are trying to restore threatened fish populations and biodiversity in the Tonle Sap Lake,” said Zeb Hogan, an associate research professor at the University of Nevada, Reno, and Wonders of the Mekong project lead. “These are some of the most incredible, largest and most endangered fish in the world. We are lucky enough to be able to put a few back into the wild.”

Releasing the fish had dual purposes: conservation and research. While not all of the species are meant to be harvested if caught, the information gathered from the recapture of certain fish is “the first step of understanding how restoration of these endangered fish might work,” Hogan said.

Even though the fish were released into a government-protected reserve, historic threats like overfishing, dam development and climate change remain for these species, especially beyond the reserve’s boundaries.

For a splash of extra protection, Wonders of the Mekong staff named the big Mekong giant catfish Samnang, the Khmer-language word for “Lucky.”

Nearly two weeks after the release, Hogan confirmed there have been just over a 100 preliminary reports of recaptured fish, though none of Samnang.

Zeb Hogan, an associate research professor at the University of Nevada, Reno, and Wonders of the Mekong project lead, is handed an endangered striped river catfish (pangasianodon hypophthalmus) by Samnang Yann, a student volunteer from Cambodia’s Royal University of Agriculture.

The evening before the release on 4 March, fish were plucked from tanks and plopped onto tables. Once Hogan had a handle on their slippery scales, tagging was quick. He measured lengths, tagged dorsal fins, read out labels and tossed them back into the tanks.

“We tag them in order to track their growth, survival and movement in Tonle Sap and beyond,” Hogan said. “This is the first step for research and conservation to see if releasing fish like this can be a long-term strategy to help with the conservation and improvement of fisheries in Cambodia.”

Tonle Sap River connects the freshwater lake to the Mekong River, which flows through China, Myanmar, Thailand, Laos, Cambodia and Vietnam. The Mekong Basin is home to thousands of freshwater fish species.

There were three kinds of fish released: more than 1,560 endangered striped catfish (pangasianodon hypophthalmus), two Mekong giant catfish (pangasianodon gigas) and approximately 30 giant carp, also known as the Mekong giant barb (catlocarpio siamensis). The giant catfish and barb are both critically endangered.

Fishermen reporting the recapture of the fish enables Wonders of the Mekong to collect data, Hogan explained that fishermen will be allowed to harvest captured striped catfish, though not the other two species.

“We were expecting some of these fish to be caught again. We don’t get any information about them unless they are recaptured,” Hogan said. 

Most of the recaptures reported since the release have been of striped river catfish landed by fishermen in Chong Kneas, Kampong Phluk and Kampong Kleang, the nearest fishing communities to the release site, Hogan said.

“The farthest recapture reported so far has been in Pursat, on the other side of the lake, which shows significant movement in a relatively short period of time,” Hogan said. “The fact that we’re getting reports of recaptures is a good thing from a research perspective and for improving these actions going forward.”

Elizabeth Everest, a researcher at Wonders of the Mekong through the University of Nevada, Reno, and Samnang Yann, a student volunteer from Cambodia’s Royal University of Agriculture, remove dead fish from a batch about to be released in Tonle Sap Lake.

Wonders of the Mekong distributed the reward information through local media outlets, posters and some of the larger lime-green tags. Fishermen will be rewarded 10,000 riel ($2.47) for returning a fish tag or calling in information. During this process, information on the fish’s size, location and method of the capture would be recorded.

“The most important thing for this research to be successful is engagement from fishermen. Without those fishermen reporting tags, we won’t have any information,” said Ngor Peng Bun, a fish ecologist and fisheries science dean at Cambodia’s Royal University of Agriculture. “This is all being done in the name of conservation. All of these fish are rare and important to protect.”

The International Union for Conservation of Nature’s assessments for the three released species list their primary threats as “biological resource use” through fishing and harvesting and “natural system modifications” via dam and water management.

“As long as I have been studying them, these fish have been so rare that it has been hard to conduct a contemporary study of their role in the ecosystems,” said Hogan, who has researched fish in the Mekong River system since 1996.

Ros Narin holds out a plastic bag for the Mekong giant barb (catlocarpio siamensis) held by Cho Heng. The two Freshwater Aquaculture Research and Development Centre officers captured several of the critically endangered species for release into Tonle Sap Lake.
“Bye-bye. Good luck,” said Samol Chhuoy, a Ph.D. student with Wonders of the Mekong, as he released a Mekong giant barb (catlocarpio siamensis), Cambodia’s national fish, into Tonle Sap Lake.
A critically endangered Mekong giant barb (catlocarpio siamensis) is held in the hands of Cho Heng, an officer at the Freshwater Aquaculture Research and Development Centre in Prey Veng Province.
A Mekong giant barb (catlocarpio siamensis) is tagged before being released into Tonle Sap Lake by Wonders of the Mekong, a research project funded by the U.S. Agency for International Development.

“But we do know these large migratory fish are among the most vulnerable in an ecosystem, so they are often the first to disappear, which is a warning sign for other species,” he said.

The success of fish reintroductions depends on protection of their habitat at every stage of their life cycle, Hogan said, explaining the need to safeguard rearing areas like Tonle Sap Lake where fish can grow larger, migration corridors the fish take from the lake to the Mekong River and spawning grounds where breeding occurs.

Lack of protection or management at any stage could contribute to the extinction of some of these species, Hogan said.

“Releases are just part of the solution. There are a lot of other threats to these fish, but this is a first step,” Hogan said. “We are trying to do something positive by getting these fish back into the wild, giving them a chance to survive and studying them so we can figure out the next step.”

Poum Sotha, director general of the Fisheries Administration, the main government partner of Wonders of the Mekong, presided over the official release ceremony at an administration enforcement station on Tonle Sap Lake’s former Fishing Lot 4.

“These fish, like the Mekong giant barb, are the identity of our country,” Sotha said during his 21-minute address attended by dozens of local officials and researchers. “The purpose of this release is to be a role model of how fishermen can participate in conservation because we, the citizens of our country, need to participate in preserving the fish.”

The sun sinks into the horizon of Tonle Sap Lake behind a Cambodian Fisheries Administration enforcement station in former Fishing Lot 4, approximately half an hour from Chong Kneas.

In the days leading up to the release, rusted yellow and red minivans were fitted with oxygenated tanks to transport the fish from the rearing centre in Prey Veng Province to the banks of Tonle Sap Lake near Chong Kneas.

The vans stopped twice during the roughly eight-hour drive at night. First, for dinner. Second, to refill the big blue fish tanks. The driving joys of Cambodia’s national highways had caused water to slosh over the tanks and onto the van floor.

Song Sinat loads threatened fish into an oxygenated water tank outfitted to fit a van to transport the fish from the Freshwater Aquaculture Research and Development Centre in Prey Veng Province to Tonle Sap Lake.
Song Sinat loads threatened fish into an oxygenated water tank outfitted to fit a van to transport the fish from the Freshwater Aquaculture Research and Development Centre in Prey Veng Province to Tonle Sap Lake.

Dawn marked a grateful end to the trip. Somewhat sore humans unloaded the fish-filled vans at a Fisheries Administration aquaculture facility on the outskirts of Siem Reap, where the fish were held before being driven 30 minutes to the lake.

At each stage of this odyssey, at least three people were needed to move Samnang, one of five Mekong giant catfish donated to the Fisheries Administration and Wonders of the Mekong by a local fish trader who collected the egg more than a decade prior.

The lessons expected to be learned from Samnang’s release will define how future releases of the other four Mekong giant catfish are conducted, Hogan said.

The release event in early March ended with more fish in the water and officials ferried to land. With a half-hour commute back to the banks of the lake, Hogan sat down for a snack and patiently waited for the ferry’s eventual return.

“Today is starting to look up,” said Hogan, taking a fork-full of instant noodles and removing his University of Nevada baseball hat for what seemed to be the first time since the proceedings began.

The sound of slurping filled the silence.

As his bowl emptied, Hogan looked up thoughtfully at the seemingly endless expanse of Tonle Sap Lake. He described his plan to use scenes from the day’s events in his forthcoming book, “Chasing Giants: The Search for the World’s Largest Freshwater Fish.”

“This release is not the end of anything except for the book,” Hogan said. “The future is uncertain and there are a lot of challenges for these fish, but I personally have to have some optimism that this is the beginning of a conservation success story.”


Photos by Anton L. Delgado for Southeast Asia Globe. Additional reporting by Vatana Un.



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