Watch a giant stingray’s safe return to its river home

After dawn May 5, scientists on a stretch of the Mekong River in Cambodia released a giant, endangered freshwater stingray caught on a fisherman’s line. It was 13 feet long and 400 pounds.

“It was shaking, and I told her, ‘Calm down, we will release you soon,’” said Chea Seila, a coordinator for the Wonders of the Mekong Project.

The stingray, Urogymnus polylepis, is the world’s largest stingray species. The animals slide across riverbeds in search of fish and invertebrates. Although they can grow to epic proportions, overharvesting for the meat, accidental deaths in fishing nets, and habitat fragmentation and degradation from dams, pollution and other human activities have made the animals endangered.

After receiving a call from the fisherman who caught the stingray, Chea and her team drove through the night to assist with its release.

Before freeing the stingray, the team took noninvasive samples that would help with future study. Then, they helped guide it back to the Mekong’s depths.

That a stingray of this size could still be found in these waters was extraordinary, the experts said.

“It shows you nature is so beautiful, but also resilient,” said Sudeep Chandra, a limnologist at the UNR and co-scientist on the Wonders of the Mekong Project.

Much of what is known about big rivers as ecosystems comes from the Mississippi River and rivers in Europe. But all of these are in temperate regions, Chandra said. In contrast, the Mekong is tropical and prone to huge, seasonal deluges. This gives the Mekong a dynamic and mostly unstudied ecology, he said.

For instance, Chandra and his team were surprised to discover recently that beneath the Mekong’s surface, there were hidden pools more than 250 feet deep.

It is probable that such pools play an important role in the life cycle of the river’s giants. With underwater submersibles, environmental DNA sampling and sensors that can provide information about the river’s changes in real time, the scientists working with the Wonders of the Mekong Project hope to learn more about these habitats and protect them from environmental threats.

Chea has been working in these communities since 2005. That work seems to be paying off. Now, when someone accidentally hauls in a giant creature, they may reach for a phone instead of a filet knife.