September 26, 2023

Researchers might have solved an enormous thriller surrounding a really massive fish.

Freshwater fish are in bother all around the world. That is very true for giant species. However one latest incident stunned scientists: Final yr, Cambodian fishermen pulled an enormous stingray from the Mekong River. The fish, a feminine, weighed 661 kilos, or about 300 kilograms, and set the report for the heaviest freshwater fish ever caught.

The invention was surprising as a result of the species generally known as the large freshwater stingray, like many different massive Mekong fish, is listed as an endangered species. Nevertheless, right here was proof that vast ones in some way nonetheless exist.

“Think about an period when the whale inhabitants is in sharp decline — the numbers are in sharp decline, the whales are getting smaller and infrequently seen — after which abruptly there’s Moby Dick,” stated Zeb Hogan, an aquatic ecologist on the College of Nevada at Reno. “It is a shock and likewise opens the door to plenty of questions.”

Almost a 3rd of the world’s freshwater fish are endangered. The researchers discovered that since 1970, 94 % of the bigger species that weigh over 66 kilos have shrunk.

Within the Mekong, all different massive fish are on the verge of extinction. “So how is the world’s largest freshwater fish preserved?” Dr. Hogan stated. “And what can we be taught from them about saving the Mekong system as an entire?”

Cambodian scientists have named the record-breaking stingray Borami, which suggests “full moon” in Khmer, impressed by its spherical form and moon part that night. Earlier than releasing her, US researchers implanted an acoustic telemetry tag close to her tail final June. Large rays should not aggressive, however the crew needed to proceed with warning. This tail has a venomous barb that may attain almost a foot in size and may penetrate bones.

Since then, the crew has been monitoring the actions of Borami as a part of the Miracles of the Mekong undertaking, which goals to protect the financial, environmental and cultural values ​​of the Decrease Mekong, a piece of the river that performs a key function within the livelihoods of about 50 million individuals.

It seems that one of many keys to Borami’s robust physique could also be the truth that she tries to remain near residence.

Based on findings revealed in Could within the journal Water, its territory is surprisingly small for a fish of this dimension, overlaying only some miles of a piece of the river recognized for its deep swimming pools, massive variety of species, and inhabitants of the endangered Irrawaddy dolphins.

The realm is into consideration for inclusion on the UNESCO World Heritage Record, which can end in safety from the Cambodian authorities. However a number of massive hydropower tasks have additionally been proposed that will require large dams.

Typically, the Mekong is more and more threatened by dams, in addition to overfishing, sand mining, air pollution and local weather change.

Borami’s propensity for shut vary contrasts sharply with different massive species within the river, akin to the large Mekong catfish, which might migrate 600 miles or extra to spawn and feed. And Borami’s choice for small territory seemingly applies to massive freshwater stingrays on the whole, based on one other research by Dr. Hogan and colleagues revealed in June.

Utilizing acoustic telemetry, the researchers tracked 22 large freshwater stingrays in a stretch of the Mekong River in Thailand and located that lots of the animals additionally dwell in comparatively small areas, a couple of miles throughout.

“We had been fairly stunned by this as a result of we thought they might migrate,” stated Dr Chayanis Daochai, an aquatic veterinarian at Chulalongkorn College in Bangkok and co-author of the research revealed in June.

Researchers in Thailand have additionally seen that female and male large stingrays of all ages are inclined to dwell collectively, one other discovery that contrasts with different Mekong megafish that usually spend a part of their lives in separate sections of the river.

Taken collectively, these information might assist clarify why large freshwater stingrays should not but as threatened as different massive Mekong species, Dr. Hogan stated. Since they don’t have to migrate lengthy distances as a part of their life cycle, they’ll ek out a existence in locations the place water high quality remains to be good and native communities are dedicated to conservation.

In July, Dr. Hogan and colleagues launched further information exhibiting that big rays are nonetheless frequently caught within the Mekong and different Asian rivers. What’s extra, fishermen all through the species’ vary report sightings of rays weighing a number of hundred kilos.

The findings counsel that defending key sections of the river can go a great distance in defending large freshwater rays, except the river as an entire turns into closely polluted or dammed.

“Given the pervasive and systemic threats to megafish as a bunch, the street to saving the rays appears much less insurmountable,” Dr. Hogan stated. “And efforts to guard it might additionally profit these different endangered species.”

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