GIANT FRESHWATER STINGRAYS
The giant freshwater stingray is a species of stingray native to large rivers and estuaries of Southeast Asia. It is one of the largest freshwater fishes in the world, with reports from the Chao Phraya and Mekong Rivers of individuals weighing 500 to 600 kilograms (1,100 to 1,300 pounds). Its numbers are dwindling due to overfishing and habitat loss, and it is in danger of extinction. The smaller freshwater whipray of New Guinea and northern Australia was once considered to be conspecific with the giant freshwater stingray but is now recognised as a separate species. [Source: Wikipedia]
Freshwater giant stingrays are among the largest of the approximately 200 species of rays. They can be found in a handful of rivers in Southeast Asia and northern Australia. The giant freshwater stingray was originally described from Thailand (where it occurs in the Chao Phraya, Nan, Mekong, Bangpakong, Prachinburi and Tapi Rivers). The giant freshwater stingray is also found in Indonesia (the Mahakam River Basin in Kalimantan) and Malaysia (the Kinabatangan River in Sabah). There are also records from various other river systems in the region. It is not clear whether all these fish are a single species or are subspecies or are a species complex. Dr Terry Bertozi, of the Evolutionary Biology Unit of the South Australian Museum in Adelaide, Australia, and is collecting genetic samples to determine whether these are the same species of stingray found in the rivers of Northern Australia.
Behavior and Characteristics of the Giant Freshwater Stingray
The giant freshwater stingray has a distinctively shaped oval disc that is widest towards the front. It is relatively thin, more or less oval-shaped pectoral fin disk and minute eyes. The snout is very broad with a projecting triangular tip. The mouth is small.The whip-like tail measures 1.8 to 2.5 times the length of the disk and lacks fin folds. The serrated spine on the tail is the largest of any stingray, reaching 38 centimeters (15 inches) long. It is covered with a sheath of toxic mucus and is capable of piercing bone. [Source: Wikipedia]
The upper surface of the body and tail are covered with small, rough tubercles, becoming sharp on the tail beyond the spine. The back is uniform brown to gray in color, sometimes becoming lighter towards the margins. The underside is white, with a distinctive broad, black band edged with small spots around the margins of the pectoral and pelvic fins. The tail is black past the spine. This species reaches at least 4.88 meters (16 feet) long and 2.13 meters (7 feet) across.
Much is still unknown about the mammoth ray species, including whether or not it can swim out to and survive at sea. The species was first described scientifically only in 1989. Its population is unknown. Many questions about it remain including: Is it truly a freshwater species? Where does it breed? What are its migratory patterns?"
The giant freshwater stingray prefers a sandy habitat. The diet of this species consists of benthic fishes and invertebrates, which it detects using electroreceptive ampullae of Lorenzini. As in other stingrays, reproduction is ovoviviparous, with females giving birth to one to two offspring at a time. A 4.3 meter (14 feet) captured female has been observed giving birth to three newborns measuring 34 centimeters (13 inches) across. Males mature at 1.37 meters (4.5 ft) across.
Endangered Giant Freshwater Stingray
The giant freshwater stingray is threatened by overfishing and habitat loss; the World Conservation Union has assessed the giant freshwater stingray as endangered over most of its range, except in Thailand where it is Critically Endangered. It is occasionally caught as bycatch by longlines and gillnets in central Thailand and likely elsewhere. This species is sold for meat and possibly cartilage; adult fish are not usually used for food but may still be killed or maimed by fishers. There is a growing sport fishery for this species. When caught on a line, it may bury itself under large quantities of mud, making it almost impossible to lift. It is also capable of pulling boats significant distances or underwater.
In Thailand, the freshwater stingray is assessed as Critically Endangered with a high risk of extinction. A combination of deforestation, dam construction, and development has degraded, altered, and fragmented river habitats such as that only a fraction of Thailand's native fish species still breed in the wild. In the 1990s, the Thai government initiated a captive breeding program to bolster the population of this and other freshwater stingray species until the habitat degradation can be remedied. However, the program was later put "on hold".
Search for the Giant Freshwater Stingray: the World’s Largest Freshwater Fish?
Michael Casey of Associated Press wrote: “American biologist Zeb Hogan is on a worldwide quest for the largest freshwater fish. He has heard the stories of Cambodian fishermen catching rays that weighed more than 1,100 pounds with wingspans of 14 feet. But so far they are just stories. If he can confirm them, his find could eclipse the world record now held by the Mekong giant catfish: a 646-pound specimen caught in 2005 in Thailand. "It could be the largest fish in the world and we know next to nothing about it," Hogan says. "I've spent five years on the Mekong looking for rays and only saw two or three. They were nowhere near the size I'd heard about." [Source: Michael Casey, Associated Press, July 20, 2008 /=]
Hogan's quest is part of the Megafishes Project financed by the National Geographic Society. The three-year project, which started in 2006, aims to document and protect freshwater giants that weigh at least 200 pounds or measure at least 6 feet long. It will take Hogan to 14 freshwater systems on six continents, including the Mekong, Nile, Mississippi and Amazon rivers. Time is running out for many of the species. The Chinese paddlefish and the dog-eating catfish in Southeast Asia are on the brink of extinction because of pollution, overfishing and dam building. In the Yangtze, where the Three Gorges Dam is a serious threat, Chinese paddlefish haven't been caught since 2003. "Of the two dozen or so species of giant fish, about 70 percent are threatened with extinction," says Hogan, an assistant research professor at the University of Nevada, Reno.
Hogan dresses like a tourist, with a baseball cap and shorts, and has the boyish enthusiasm of an explorer. He spends much of the year searching for these large fish. He has focused mostly on Asia, where he once traveled 36 hours by road to catch the taimen in Mongolia. He just returned from Bhutan, where he scoured river canyons for mahseer. Hogan said he was drawn to the freshwater ray, known scientifically as Himantura chaophraya, because so little is known about it.
Hogan spent the last few years on the Mekong in a futile effort to catch rays because the nets of Cambodian fishermen were no match for them. Rays also are nearly impossible to spot because they spend much of their time scrounging for small fish, shrimp, crabs and mollusks that live on the bottom of muddy rivers. Hogan got wind of big rays being caught and released by Rick Humphreys' company FishSiam in Thailand. Unlike the Cambodian fishermen, FishSiam uses modern rods and reels used to catch other big game fish. At first he was skeptical, then excited.
Catching a Small Giant Freshwater Stingray
Reporting from Samut Songkram, Thailand, Michael Casey of Associated Press wrote: “Rushing across a temple parking lot, British angler Rick Humphreys yells, "We've got a fish." He jumps into a small motorboat on the Mae Klong River in time to see Wirat Moungnum bring the prize to the surface: a rare giant freshwater stingray that weighs as much as 44 pounds. It bursts through the murky water exposing a soft, white underbelly the size of a trash can lid. The crew scrambles to string a rope through its gill-like slits and wrap a towel around its 5-foot-long tail, which has a venomous barb. "It's a start," Humphreys says almost apologetically. The specimen is a tenth the size of the largest rays. "There are a lot bigger ones than that." [Source: Michael Casey, Associated Press, July 20, 2008 /=]
Humphreys seems an unlikely partner in Hogan's quest. He has no scientific training. But he knows how to fish, and his team's success in catching stingrays is almost unmatched in Thailand. Just in the last year, Humphreys and his partner, Wuttichai Khuensuwan, have caught 40 rays on the Bang Pakong and Mae Klong Rivers, with the largest weighing in at 485 pounds. Humphreys, who got his start catching carp in West London gravel pits, says he prefers stingrays because of their fight. They routinely break fishing lines, he says, and one took 15 of his men about six hours to bring to the surface. "Their strength is legendary," he says. "When you see them in the flesh, it is quite humbling."
Catching a ray can be dangerous, he says, especially before its tail has been neutralized. Wuttichai Kuachareonsri, a member of Humphreys' crew, stopped fishing for a year after he was stung in the leg. "I never have felt pain like that," he says. "It really frightened me." On his fishing trip with Hogan, Humphreys boasts about "monsters" below the tranquil river and insists that it is a matter of time before his team lands a world record ray.
The anglers head to the Bang Pakong and Mae Klong rivers just a two hours' drive outside Bangkok, winding their way past office towers, Buddhist temples and busy highways. Fish farming pens dot the riverbanks, and sounds of construction and puttering boats echo across the water. Both spots have given up rays in the past. But on the their first day on the Bang Pakong, the fishermen come up empty. Humphreys blames the heavy rains that have swollen the river. The next day, they have better luck on the Mae Klong.
The rod bends almost into the water, and Wirat struggles for almost half an hour as the ray dives under the boat and across the bow. It finally is brought to the surface, revealing its big bulging eyes and dark, coarse skin. Its tail alone is 12 feet long. Hogan says catching such a big ray so close to a big city is a sign the species is thriving despite pollution. He is awaiting government permission to launch a two-year study to catch and tag 20 to 30 more rays to better understand their movements.
Giant Freshwater Stingray Caught by Fishermen
In February 2008, WildExtra.com reported: “One of our readers has sent in this photo of an enormous and rare giant freshwater stingray caught in December 2007. The monster ray was caught in the Ban Pakong River 80 kms east of Bangkok. The fish was captured by Tom Parker from Coventry whilst fishing on a fishsiam.com guided freshwater angling expedition. The immense size of the fish made it impossible to weigh. With a wingspan of 2.4m the giant ray was estimated to weigh in the region of 170 to 200 kilograms. [Source: WildExtra.com, February 2008]
The capture was made in the lower tidal reaches near Chachoengsao and took almost an hour to land. The fish was released after capture.Amazingly, 12 different specimens of this species have been caught in the last three to four months from two different rivers, the Ban Pakong and Maeklong Rivers. One of these captures may well have been a newborn of just 12 centimeters in size caught from the Maeklong River. This is a good sign for this river which has been affected by pollution in previous years and also a good sign for this elusive and nomadic species.
In February 2009, WildExtra.com reported: “A giant freshwater stingray was caught in the Maeklong River in Thailand in January 2009, weighing as much as 350 kilograms, by Dr. Ian Welch, a freshwater biologist, who had been visiting Thailand in conjunction with the National Geographic Society to help with a stingray tagging programme. Dr Welch and the Fishsiam team, who are also helping with the research, landed this extraordinary fish on whilst filming a documentary with the Dr. Zeb Hogan and the National Geographic Society about "Megafishes". The fish was estimated by scientists present at the capture to weigh an extraordinary 265+ kilograms. The fish was observed to be pregnant and was released soon after capture.The expedition also involved a research project given official approval by the Thai authorities to tag Giant freshwater stingray and monitor stingray populations in both the Ban Pakong and Maeklong Rivers.
Zeb Hogan told the New York Times, "I saw a stingray in Cambodia in 2003 that was 4.13 meters long. It had a disc 2 meters across and 2 meters long, and the tail was 2.13 meters long. That fish could have been it, but we couldn't weigh it. It was too big." When he began to spread the word in Cambodia that he was looking for giant fish, Hogan said, it was stingray he had in mind. "I thought I'd get 50 phone calls the first week, but nobody contacted us," he said. "So they're more rare than I thought they were."
Candidate for the World’s Largest Freshwater Fish
In February 2009, National Geographic reported: “Fishers and scientists announced the catch, and release, of what is likely the world's largest known freshwater giant stingray. The giant stingray, weighing an estimated 550 to 990 pounds (250 to 450 kilograms) was reeled in on January 28, 2009, as part of a National Geographic expedition in Thailand. The stingray's body measured 6.6 feet (2 meters) wide by 6.9 feet (2.1) meters long. The tail was missing. If it had been there, the ray's total length would have been between 14.8 and 16.4 feet (4.5 and 5 meters), estimated University of Nevada Biologist Zeb Hogan. Hogan was in Thailand searching for giant fish as part of the Megafishes Project. [Source: National Geographic, February 24, 2009]
The new find gives Hogan hope that the giant stingray, once overfished, may be more abundant than previously thought. And it may confirm the giant stingray as the heavyweight champ of the Megafishes Project. "Honestly, we just don't know how much it weighed. But it's clear that the giant stingray has the potential to be the largest freshwater fish in the world," said Hogan. "The Thai populations were once considered critically endangered, although with the discovery of new populations the stingray's abundance appears higher than previously believed," added Hogan. The International Union for Conservation of Nature (IUCN) currently lists the freshwater giant stingray as vulnerable. In March 2008, Hogan found a 14-foot-long (4.3-meter-long) ray near the Thai city of Chachoengsao.
Image Sources: Wikimedia Commons, giant catfish and stingray; National Geographic and relive earth
Text Sources: National Geographic, Natural History magazine, Smithsonian magazine, Wikipedia, New York Times, Washington Post, Los Angeles Times, Times of London, The Guardian, Top Secret Animal Attack Files website, The New Yorker, Time, Newsweek, Reuters, AP, AFP, The Economist, BBC, and various books and other publications.
Last updated November 2012