‘Death spiral’: Mekong River megafish have shrunk by half, study reveals | Fish

The size of the megafish in the Mekong river has decreased alarming in recent years due to overfishing, a study revealed. The length of the most important and threatened freshwater giants, some as large as grizzly ones, has decreased by 40% in seven years.

Some fish, such as the giant mekong catfish, have been studied for a longer period and show a weight of 55% in the last 25 years, going from an average of 180 kg (397 lb) to 80 kg.

One of the study teams, the biologist Ngor Peng Bun, helped catch a gigantic catfish in 2000 which weighed 270 kg, before scoring and freeing it. “It was huge-unforgettable,” he said, and almost capsized his boat. The species, known in Khmer under the name of Trey Reach, or Royal Fish, is now the shadow of his old self.

The giant barb, the largest carp in the world and the national fish in Cambodia, has shown a similar trajectory. The two species are in particular in danger.

Size is a question of survival because large fish – which are more likely to be captured – exponentially produce more eggs, scientists said. A 300 kg catfish can produce 10 to 20 times more offspring than a 50 kg fish, for example. Many of the largest species are also long life and slow to mature, which means that death increases can tipport the collapse of the population.

Mekong giants are crucial for the river ecosystem but also at the heart of the livelihoods of millions of people who depend on fishing. Scientists found a sign of hope when in 2022, a Fisher captured and published a record of 300 kg Stingray. It was the largest freshwater fish never seen and showed that some giants remain.

Fishing and hunting often target the largest animals and have led to the narrowing of many species, including cod in the Baltic Sea, salmon in Alaska and sharks, and has led to smaller defenses in African elephants.

Dr. Zeb Hogan, an associate teacher of research at the University of Nevada, United States, and part of the study team, said that the rapid narrowing of Mekong Megafish was surprising and shocking.

“We have seen this scheme in Atlantic cod fishing, where decades of selective size fishing eliminated the largest and fertile fish, causing spectacular collapse. As body size and reproduction capacity decrease, [the Mekong] The risk of fish entering a “spiral of death”, in which the populations persist but are no longer viable, “said Hogan.

Sophorn Uy, at the Royal University of Agriculture of Phnom Penh and in a part of the team, said: “Knowing that these giants shrink, both in size and in number, it is like losing a small piece of Cambodia itself. Their existence carries a deep cultural and ecological meaning.”

The study, published in the journal Biological Conservation, analyzed seven years of data monitoring of 23 sites in the lower mekong basin and included 257 species of fish. Complete data was available from 2007 to 4. Hogan said that the tendency to reduce the end reduction.

In addition to overfishing, the Mekong megafish are struggling with dams, which block their migration to Frai terrains; The climate crisis, which upsets seasonal triggers of temperature and precipitation; And the destruction of flooding seasonal forests for agriculture, which is an important habitat.

Hogan said: “This 300 kg stingray has shown us that it is not too late. New records are still underway. But they will notify little unless we are working to protect these species and the river system they call at home. The future of Mekong giants is suspended.”

The stingray was labeled and followed for two years, which he spent in a protected area along a 3 -mile river section (5 km). “Connectivity [along rivers] And protected habitat – it’s the Holy Grail, “said Hogan.” If you have, then these fish can survive. “”

Catrimer Le Mégafish is already illegal in certain countries through which the Mekong flows, but the application remains a great challenge, scientists said. “Local fishermen were essential to collect our data,” said Sophorn. “They are on the front line and must be part of the solution.”