Giant ray discovered in a deep pond at the bottom of the Mekong River | National Geographic

Stung Treng, Cambodia

When you see the Mekong River slowly flowing from Laos through sandy beaches and lush islands to neighboring Cambodia, it’s hard to imagine the amount of life beneath the mysterious river’s surface.

An estimated 200 billion fish spawn in this part of the river alone, which is about 150 kilometers long, making the nearly 4,400 kilometers long Mekong River one of the most fish-rich on the planet. Ponds at the bottom of the river, which can reach depths of 80 metres, serve as refuges for some of the world’s largest and most endangered freshwater fish.

The biodiversity of the Mekong River is generally not visible to the naked eye. But last week it actually came out of the depths, when fishermen pulled out a giant four-meter freshwater ray weighing more than 180 kilograms from the dark depths of the Mekong River. The female ray was accidentally caught after eating a smaller fish on a hook. Since the Hunters did not want to kill the giant ray, they called the rescue team. Experts were able to remove the hook from the stingray, weigh and measure the animal, and then return it to the river unharmed.

For Zeb Hogan, who has spent years searching for giant fish in the Mekong River, including the nearly extinct giant Mekong catfish and giant Siamese carp, the capture of this giant illustrates the enormous ecological and biological importance of the deep pools in the river’s upper reaches. The Cambodian part of the Mekong River, an importance confirmed by Hogan’s recent expeditions to these ponds. This part of the river is also home to the rare Irrawaddy dolphin and Kantor’s giant soft-shelled turtle.

“This is the last place on Earth where we still find these creatures side by side,” said Hogan, a fish biologist at the University of Nevada in Reno and head of the USAID research program Wonders of the Mekong.

In the week before his capture, National Geographic researcher Hogan led a science expedition to this area. Two other NatGeo researchers have joined the international team of experts: Kakani Katija, a deep-sea expert, and Kenny Broad, an environmental anthropologist and cave diver.

The expedition was the first of its kind and aimed to explore the deepest parts of the Mekong River. The team’s “eyes and ears” functioned as a few small remote-controlled submarines equipped with lights and cameras, as well as submersible cameras and video cameras with bait attached to them. The researchers also collected DNA samples to track down rare or as-yet-unidentified species in a river that, despite its enormous importance, has not yet been thoroughly studied.

holes in the bottom

The Mekong River rises over the highlands of Tibet and passes through six countries on its way to the South China Sea. With nearly a thousand species of fish, the Mekong River Basin is known as one of the most important biodiversity hotspots on the planet. This system is the world’s largest inland fishing ground, providing livelihoods for tens of millions of people in the area.

The secret behind the Mekong’s tremendous productivity lies in the monsoon floods, which raise the river’s level by up to 40 percent each year and carry huge numbers of juvenile fish downstream and scatter them over the flooded river basins, where the fish continue to flow. grow. to grow. Many Mekong fish species migrate long distances during their life cycle to their upstream spawning grounds, including deep ponds in northern Cambodia.

Researchers have been familiar with this area for some time, where every year a vast system of streams, tributaries and wooded islands is flooded. In the dry season, the area is a haven for many important Mekong fish species, including some giant species. But due to its remoteness, scientific investigation of the area – especially in the deep ponds at the bottom of the river – is not easy.

Katia directs the Bioinspiration Lab at the Monterey Bay Aquarium Research Institute and sees great similarities between the deep ponds in the Mekong River and the deep-sea landscapes his team typically studies: a deep-sea ecosystem, with little daylight and terrestrial currents along the bottom. . “What makes working in the Mekong River so challenging, especially when it comes to shooting techniques, is the turbidity of the water and very limited visibility, even in the deepest areas,” she says.

This became apparent during the multi-day expedition to the Mekong River, when Katiga and her team deployed a small remote-controlled submarine to study the river bed. From a search boat on the surface, they could watch computer screens as the little submarine floated through thick clouds of silt, where the view was no more than a foot or so.

But videos taken at a depth of eighty meters still show several species of fish, including the giant migratory catfish that lived in Cambodia. you see shit is called. These species were once the main fish of local fishermen in the border area with Laos, but these important inland fishing grounds no longer exist as the fish migration route was cut off in 2020 by the construction of Don Sahong Dam near the Lao-Cambodian border.

Files are recorded you see shit He was especially important to Hogan, as he had been researching these inland fishing grounds for more than two decades and trying to figure out how the distribution of fish species had changed since the dam was built.

Broad has extensive experience diving in the “blue holes” under the sea off the Bahamas and has compared diving in the Mekong to “swimming in a bathtub full of water”. Cafe con lychee† If you add to that the strong current, depths of more than 80 meters and different types of debris, you’re talking about a very challenging environment to explore, he says.

Depth giants

Scientists from the Mekong Wonders Project have spent the past few years researching villages and fish markets to better understand the aquatic biodiversity of the deep ponds at the bottom of the Mekong River. In collaboration with the Cambodian Department of Fisheries, the project has also created a local network of fishermen who inform scientists about giant fish catches and endangered species.

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