We sat down for a conversation at River Safari’s Mekong River area for a chat.
The 4,800km long Mekong is an ancient and vast river that begins in the mountains of the Tibetan plateau before descending through Yunnan in China, then Myanmar, Lao, PDR, Thailand and Cambodia before flowing through the lower Mekong Delta region of south Vietnam into the South China Sea.
A combination of factors, including the rich availability of food, as well as the nature of its deep water pools and flood plains, means that the mighty Mekong is home to over 1,000 species of fish – which is more per unit area than the Amazon River.
Categorized as Endangered on the IUCN Red List, the development of mainstream dams on the Mekong river and fishing pressure due to capture for aquariums and sport fishing in other rivers like the Mae Klong, are all contributing to the species’ decline in the wild.
At the Mae Klong river in Thailand, the veterinarian staff and students of Chulalongkorn University, led by Dr. Nantarika, have been studying the giant freshwater stingray for the past eight years. To date, the team have caught and microchip tagged 200 adult giant freshwater stingray, of which only ten have been recaptured individuals.
The team heads out twice a month to carry out its work, and for their November round, River Safari’s Hon Yien joined them to see how they capture and restrain these giant stingrays in order to draw blood and do ultrasounds.
To begin with, hooks are baited with whole, live or half dead catfish and several are placed near the bottom of the river at 8am each morning. Fishermen working with the team will spend as long as two hours to reel in a stingray that has taken the bait. As Hon Yien realised, the method is far from ideal.
Eventually, it yields and is hauled in. At this juncture, the giant freshwater stingray does not struggle much as it’s exhausted. With the vet team on stand-by, the fishermen will cover its barb with elastic, self-adhering surgical bandage to prevent any wounds from being inflicted to the team and themselves. The hook is then immediately removed from its mouth to reduce causing stress to the animal. The stingray is then scooped up in a hammock-shaped fishing net and carried to the study site, where it is taken out of the fishing net and handled by the team.
Regardless of whether it is male or female, the data collected includes:
- Microchip Identification (If Any)
- Disc Width
- Girdle Length
- Total Length
- Blood sample
- Tissue sample
- Venom sample
In the long-term, the team has a few key goals: collect venom to produce anti-venom; conduct hormonal studies on pregnant females; and finally, to accurately determine the sexual maturity of the males through a correlation of the clasper length, girth and disc width.
There were unanticipated surprises on the trip. On the first day, three were caught for the tests – one male and two females. The last one turned out to be pregnant.
The trip was revelatory on many levels for Hon Yien. Findings from the studies conducted by the Thai research team so far indicated that the giant freshwater stingray’s claspers’ length (the anatomical structure used in mating) has to be 10% of the disc width to indicate sexual maturity in males.
“We didn’t know that before the trip. They might have published scientific reports in Thai or other languages, but there wasn’t much available in English on this specific issue. Most of what I found focused on the Amazonian neotropical freshwater stingray,” he said, referring to the regions of both Americas and the entire South American temperate zone, from where these stingrays originate.
There are also useful lessons for future plans at the River Safari itself.
Currently, the River Safari has a total of 5 giant freshwater stingray in its collection. There is a pair in the exhibit, a male in quarantine and two females that are housed separately. So far, none are breeding. While blood drawing and general measurements and assessments are routine, little research on the reproduction has been undertaken here. This is where the lessons from the trip will prove to be useful.
Hon Yien also learned a lot from his interactions with Dr. Nantarika, who had visited WRS in 2011-2012 to assess the stingrays in quarantine at the time.
“Dr. Nantarika shared information on the growth rate, what happens when the stingray gives birth, how big the offspring can be, what happens when a pregnant female is put through a lot of stress. We didn’t know a lot of this.”
“I’m doing a manual for our giant freshwater stingrays right now, so the trip coincides with that,” he said.
The dearth of scientific information of this kind on the giant freshwater stingray should give us all some pause for thought. The species, though endangered, is not adequately understood.
After the trip, Hon Yien also said that he realised more needs to be done to study the species across the greater Mekong region. Serious conservation work on the species would require researchers to go beyond the Mae Klong river and start riverine surveys as far upstream as Chiang Khong, as well as the Chao Phraya, Nan, Bang Pakong, Prachin Buri and Tapi Rivers.
The giant freshwater stingrays of Asia, while impressive in size, are not particularly striking to look at. Plain greyish or brown in colour, their skin is coated with a layer of dark brown mucus. As bottom dwellers they are hard to spot in the wild and they may not be considered as spectacular as their more colourful counterparts from the Amazon. But Hon Yien feels that if we don’t act to conserve the species, many of the giants of the Mekong may soon disappear.
“Before I began managing the stingrays in our collection, I was really fascinated by the Mekong giant catfish. They live on detritus and plant matter and are a gentle species, but I was amazed by how they’ve evolved to grow to this massive size. Similarly, with the stingrays, we may not be able to see something this impressive in the future.”
They are, he says, “important pieces of the puzzle for the whole freshwater ecosystem”.
“In say twenty years, if we lose these species in the wild, that piece will go missing from our large Asian rivers. We won’t understand how the overall ecosystem of these rivers work.”
And that is something we must endeavour to prevent.