Just after dawn on May 5, scientists working along a stretch of the Mekong River in Cambodia released an endangered giant freshwater stingray that had been caught on a fisherman’s line. At 13 feet long and 400 pounds, the giant animal pancake was larger than a hibachi table.
“He was shaking and I told him, ‘Calm down, we will release you soon,’” said Chea Seila, coordinator of the Wonders of the Mekong Project.
The giant freshwater stingray, Urogymnus polylepis, It is the largest species of stingray in the world, also known as whip. With dark brown tops and creamy white bottoms, the animals glide across riverbeds in search of fish and invertebrates. Although they can grow to epic proportions, overharvesting for ray meat, accidental deaths in fishing nets, and habitat fragmentation and degradation from dams, pollution, and other human activities have put the animals at risk of extinction. .
After receiving a call from the fisherman who caught the ray, Ms. Chea and her team drove eight hours through the night to help with its release. They arrived at 3 am and waited with the fish until the sun came up. More people were needed to gently move the animal, which was armed with a poisonous spike that could be more than a foot long and capable of piercing bone.
Before releasing the ray, Ms. Chea and her colleagues took noninvasive samples that would help with future study of the species. They then helped guide the colossus back into the depths of the Mekong.
“He calmly swam away, but then he reappeared, which made us very, very happy,” Ms Chea said.
That a ray of this size could still be found in these waters was extraordinary, experts said.
“It shows you that nature is so beautiful, but also resilient,” said Sudeep Chandra, a limnologist at the University of Nevada, Reno and a co-scientist with the Wonders of the Mekong Project. “Even with major environmental problems in the Lower Mekong, such as dams, forest changes and overfishing, these large and charismatic species are still there, wanting to persist.”
Of course, that’s not always the case, Chea said. The people who live along the Mekong rely on the river’s bounty for food and income. Stories abound in those communities about much larger rays that have been cut into small pieces for sale at the local market, she said. In fact, Ms. Chea said, another giant stingray was caught in April. However, he was already dead when they found him.
Giant freshwater rays aren’t the only huge, endangered creatures in need of preservation along that stretch of the river. It is also home to giant softshell turtles, the giant Mekong catfish, and the giant barb, a type of fish. The Wonders of the Mekong association is working with scientists to better understand the habitat.
Much of what is known about large rivers as ecosystems comes from the Mississippi River and the rivers of Europe. But all of these are in temperate regions, Dr. Chandra said. In contrast, the Mekong is tropical and prone to large seasonal deluges. This gives the Mekong a dynamic and largely unstudied ecology, he said.
For example, Dr. Chandra and his team were surprised to recently discover that beneath the surface of the Mekong there were hidden pools more than 250 feet deep. If you could somehow submerge the Statue of Liberty and its pedestal into one of these chasms, only the torch would remain above the water.
Such pools are likely to play an important role in the life cycle of the river giants. With underwater submersibles, environmental DNA samples, and sensors that can provide information about changes in the river in real time, scientists working with the Wonders of the Mekong Project hope to learn more about these habitats and protect them from environmental threats.
Ms. Chea has been working in these communities since 2005, building trust and creating alliances between the project and the people who share the river with these species. And that work appears to be paying off. Now when someone accidentally drags a giant creature, she can reach for a phone instead of a fillet knife.
Ms Chea said a local leader told her he had never seen a giant freshwater stingray. And during the launch, she saw him talk to two young children.
She said she heard him identify the animal and say, “They should protect it so that their children in the future will also know that we have a giant stingray in our town.”