It’s not often that aquatic veterinarian Dr Nantarika Chansue gets to encounter the same stingray twice – six years apart, one that was pregnant on both occasions. ‘It’s the big one,’ Dr Chansue exclaimed, standing over the edge of the longtail boat as the creature emerged from the murky depths of the Maeklong River in Thailand. It was indeed the largest giant freshwater stingray, as well as the largest freshwater creature ever recorded: measuring 4.3 metres long by 2.4 metres wide, and estimated to weigh between 318 and 363kg. It was a high point in Dr Chansue’s nine-year study into these fascinating and secretive creatures, that live in Southeast Asia’s turbid riverbeds.
This individual had grown since it was initially caught in 2009, something that offered further proof that the long-lived giant freshwater stingrays keep growing throughout their lifetimes (the growth rate has been extrapolated at 5cm in diameter every year for juveniles and then slowing to 3cm yearly for adults). ‘When we first started the study,’ Dr Chansue says, ‘we knew almost nothing about stingrays. So we started doing blood analysis to check physiological functions and establish baseline data, and DNA analysis to understand the population genetics. Now we also study reproductive characteristics: we check level of hormones and perform an ultrasound to check for pregnancies and ovaries in adult females.’
Of the 230 giant freshwater stingrays that Dr Chansue has studied, 11 have been recaptures. ‘We identify recaptures by a microchip we affix to them,’ she explains. ‘Recaptures allow us to establish growth rates and longevity, and also estimate population size by inputting the data into a formula.’
The ‘big one’ was filmed for an American TV programme called Ocean Mysteries, and in the previous catch had been filmed for National Geographic TV by fish biologist Dr Zeb Hogan. ‘The recapture,’ Dr Hogan says, ‘tells us that the fish survive the stress associated with recreational fishing, and that the lower part of the Maeklong River is an ideal study site. It may also be a breeding or pupping area – many of the largest stingrays captured are pregnant females.’
The Megafishes research project run by Dr Hogan has generated widespread media coverage. The giant freshwater stingrays, the largest on Earth, are enigmatic creatures that make good stories and TV – in the olden times the Thai people used to think that the rays were demons – and virtually every renowned wildlife documentary-maker has made a documentary about them. Travel journalists have also beaten a well-worn path to Maeklong, with several articles appearing in the UK national press. And for sports-fishermen, hooking a stingray now ranks as one of the most alluring fishing adventures to be had. But the publicity has not led to concomitant conservation measures: despite their rarity and decline (classified as ‘Endangered’ by the IUCN), the stingrays are not legally protected from capturing and trading anywhere in their range.
‘It’s relatively easy to write an article or produce a television documentary,’ says Dr Hogan. ‘But it’s much more difficult to implement a long-term research project or enact national level rules and regulations. Of course, articles and television documentaries do increase awareness about fish like this and hopefully, eventually, that will lead to more study and better protection. If you look at the history of shark conservation you’ll see the same pattern.’
So far, for the stingray, greater fame has had the opposite effect: the demand for stingrays by aquariums has grown. Dr Chansue says that she has heard that there are 100 pending orders for stingrays by aquariums in China alone. And after years of lobbying the government in Thailand to prohibit the catching of stingrays, she has achieved limited progress in the form of a law drafted by the Thai Department of Marine and Coastal Resources that will make it illegal to catch the stingrays without a permit (the law was still at the draft stage at the time of writing). ‘Permits will not be withheld for commercial capture,’ Dr Chansue explains. ‘But at least it will allow us to find out who is catching the stingrays, what for, and how many are being caught.’
The consolation is that stingrays are difficult to catch – they lurk and forage in the turbid riverbeds of deep rivers – and in the lower reaches of the Maeklong River where Dr Chansue operates and where it is easiest to catch stingrays, they are actually protected by local regulations promulgated by the concerned governor of Samut Songkram province. Only Dr Chansue has permission to catch stingrays in that province and, although enforcement is weak, the regular presence of Dr Chansue and her colleagues serves as a deterrent to potential poachers.
Those colleagues, aside from her Masters students, are the people of Fish Siam, a sports-fishing operator based in England whose paying guests fund the costly fishing operation – it takes at least two boats and a crew of three to mount a trip. ‘I don’t have any sources of funding,’ Dr Chansue says. ‘So I wouldn’t be able to catch stingrays without the support of Fish Siam. The collaboration is working well: it’s a symbiotic relationship.’
‘We make it a point to catch and handle stingrays as humanely as possible,’ assures Fish Siam’s owner, Rick Humphreys. Captured stingrays are allowed to float on the water’s surface with a loose net underneath, the sports-fisherman has a picture taken triumphantly holding up the ray’s tail, and Dr Chansue works nimbly – measuring the dimensions of the stingray, drawing samples of blood and venom, snipping a fragment of flesh for DNA analysis, inserting a microchip, and injecting a vitamin to alleviate the stingray’s stress. The net is then pulled away, and the stingray vanishes into the murky waters with one flap of its fins.
There is more that Dr Chansue wants to do: I join her on the Maeklong as she searches for a site on the river’s bank where she can set up a research and conservation centre, but eventually she has to give up on the idea. ‘The Thai government is not presently interested in doing much for stingray conservation,’ she laments.
‘It can be very difficult to find political and financial support for projects focused on fish that are relatively unknown and have little economic value,’ Dr Hogan echoes. ‘Giant freshwater stingray research and conservation is not a top priority for donors or governments. Moreover, it’s not always a good idea to change the laws regarding management of a species without knowledge of the species’ ecology, which we don’t really have in the case of giant stingrays.’
Knowledge of the stingray remains woefully patchy and inadequate. Even knowledge of their reproductive cycle and longevity remains conjectural. Their movements remain largely uncharted – limited acoustical tracking in the Maeklong River only tracked them up to three kilometres upriver – and it’s not known whether there is any intermingling or interbreeding of stingrays in the different rivers where they occur or whether each river’s population is separate and distinct.
In Thailand the stingrays occur in all the major rivers – the Maeklong, Chao Phraya, and Bang Prakang – and also in the Mekong, including the tracts of it that fall in Laos, Cambodia and Vietnam. Giant freshwater stingrays are also native to India and Borneo, but very little is known about the species’ status in those countries – records of sightings or catches are scant and mostly based on hearsay. And although there are reports that stingrays are caught for the flesh and cartilage in Kalimantan (the Indonesian part of Borneo), and that fishers in parts of the Mekong also keep any juvenile stingrays caught as a bycatch, the giant freshwater stingray is not considered an edible animal in much of its range.
‘In places with high fishing pressure, such as near the Cambodia/Vietnam border and in Tonle Sap Lake, stingray populations may have dropped by as much as 50 to 90 per cent in the last 30 years,’ Dr Hogan says. ‘In the Chao Phraya the populations appear to have declined due to habitat fragmentation and pollution. But in the less populated areas of the Cambodian Mekong, as well as in the lower Maeklong River and Bangpakong River, you can still find a fair number of adult stingrays. I think that rays still occur in decent numbers in free-flowing sections of rivers with good water quality and low fishing pressure.’
According to the IUCN Red List, the overall stingray population has declined by 30 to 50 per cent, and the major threats are pollution and capture. There are other gathering threats: the hydro dams planned on the Mekong in Laos and Cambodia, unscrupulous sports-fishermen in Thailand who cause unnecessary deaths by gaffing stingrays and cutting their tails as trophies.
‘We used to catch two or three stingrays on every fishing day when we first started the research project,’ Dr Chansue says. ‘Now we are lucky if we catch one, and that’s an indication that stingrays are decreasing. My fear is that they are decreasing fast, so we need to intensify our research and efforts to protect these fantastic creatures.’
For more on the topic of extinction, pick up Geographical’s special themed September 2016 issue, on sale now.