Researchers might have solved an enormous thriller surrounding a really massive fish.
Around the world, freshwater fish are in hassle. That’s very true of enormous species. But one latest episode shocked scientists: A large stingray was pulled out of the Mekong River by Cambodian fishermen final 12 months. The fish, a feminine, weighed 661 kilos, or about 300 kilograms, and set a document for the heaviest freshwater fish ever caught.
The discovery was shocking as a result of the species, often called the enormous freshwater stingray, like most of the different massive fish of the Mekong, is listed as endangered. Yet, right here was proof that massive ones, in some way, nonetheless exist.
“Imagine an era where whale populations are in broad decline — numbers are declining dramatically, whales are getting smaller and are seldom seen — and then, all of a sudden, Moby Dick appears,” stated Zeb Hogan, an aquatic ecologist on the University of Nevada, Reno. “It’s a shock and also opens the door to so many questions.”
Nearly a 3rd of freshwater fish worldwide are threatened with extinction. Since 1970, 94 p.c of larger species, people who weigh greater than 66 kilos, have declined, researchers have discovered.
In the Mekong, all the different massive fish are on the point of extinction. “So how does the world’s largest freshwater fish persist?” Dr. Hogan stated. “And what can we learn from them about saving the Mekong system as a whole?”
Cambodian scientists named the record-breaking stingray Boramy, which is Khmer for “full moon,” impressed by her spherical form and the lunar part that night. Before releasing her, in June final 12 months, American researchers implanted an acoustic telemetry tag close to her tail. Giant stingrays are usually not aggressive, however the group needed to work with warning. That tail has a venomous barb that may attain virtually a foot lengthy and might penetrate bone.
The group has been monitoring Boramy’s actions ever since as a part of the Wonders of the Mekong mission, which goals to take care of the financial, ecological and cultural property of the Lower Mekong, a stretch of the river that’s central to the livelihoods of some 50 million individuals.
It seems, one of many keys to Boramy’s sturdy structure could be the truth that she tends to remain near residence.
According to findings revealed in May within the journal Water, her territory is surprisingly small for a fish of such measurement, encompassing only a few miles in a stretch of river identified for its deep swimming pools, its excessive species rely and its inhabitants of endangered Irrawaddy dolphins.
The space is into account for designation as a UNESCO World Heritage website, which might result in safety from the Cambodian authorities. But a number of main hydropower tasks, which might require large dams, have additionally been proposed.
Overall, the Mekong is more and more threatened by dams, and in addition by overfishing, sand extraction, air pollution and local weather change.
Boramy’s short-range tendencies stand in sharp distinction to different giant species within the river, just like the Mekong large catfish, which may migrate 600 miles or extra to spawn and feed. And, Boramy’s choice for a small territory in all probability applies to massive freshwater stingrays basically, in response to one other research by Dr. Hogan and colleagues that was revealed in June.
Using acoustic telemetry, the researchers tracked 22 large freshwater stingrays in a piece of the Mekong in Thailand and located that most of the animals additionally confined themselves to comparatively small areas, on the size of some miles.
“We were quite surprised by this, because we thought they’d migrate around,” stated Dr. Chayanis Daochai, an aquatic veterinarian at Chulalongkorn University in Bangkok and a co-author of the research revealed in June.
The researchers in Thailand additionally noticed that female and male large stingrays of all ages tended to stay collectively, one other discovery that stands in distinction to different Mekong megafish, which normally spend elements of their lives in separate sections of river.
Taken collectively, these findings might assist clarify why large freshwater stingrays are usually not but as imperiled as different giant Mekong species, Dr. Hogan stated. Because they don’t have emigrate lengthy distances as a part of their life cycle, they will eke out an existence in locations the place the water high quality continues to be good and native communities are dedicated to conservation.
In July, Dr. Hogan and his colleagues revealed extra proof indicating that enormous stingrays are nonetheless repeatedly caught within the Mekong and different Asian rivers. What’s extra, fishermen throughout the species’ vary have been reporting encounters with stingrays weighing a number of hundred kilos.
The findings counsel that defending key sections of the river might go a good distance towards defending large freshwater stingrays, as long as the river as an entire doesn’t grow to be closely polluted or dammed.
“Given the pervasive and systemic threats to megafish as a group, the path forward for saving the stingray seems less insurmountable,” Dr. Hogan stated. “And efforts to protect it could also benefit these other species that are facing extinction.”
Source: www.nytimes.com