Shark Trust – Giant Freshwater Stingray Conservation

Conservation is crucial to the future of the giant freshwater stingray (Himantura Chaophraya)  found in several river systems throughout Thailand and South East Asia and is reputed to reach weights exceeding 1,000lb (450kg). This gigantic underwater leviathan is one of the largest freshwater fish on earth and is one of the least studied creatures on the planet. With very little previous research conducted on this prehistoric predatory fish and very few documented captures it is truly a creature shrouded in mystery and legends.

The Giant freshwater stingray was first formally described in 1989 since then there has been very little scientific research concerning this mysterious prehistoric species.

The Giant freshwater stingray is a fish almost lost in time with ancestry dating back to a prehistoric age before the appearance of man. With so little known about this elusive and nomadic predatory giant and with so few reported captures it has been classed as vulnerable on the IUCN red list. It is believed this species is threatened by industrial and agricultural pollution in addition to the building of dams which block the mighty ray’s migratory and possibly breeding habitat.

Previous attempts to monitor/study Giant Freshwater Stingray populations by the UICN and other concerned bodies have failed miserably with only two or three reported captures per year.

The Fishsiam team has currently accounted for thirty eight individual Giant Freshwater Stingray captures from two of Thailand’s wildest and unexplored tidal rivers in a short one year period. We have found surprisingly healthy and breeding populations in both the Ban Pakong and Maeklong Rivers catching numerous Giant Freshwater Stingray to an estimated 220kg’s (2.4m).

The Giant Freshwater Stingray is a nomadic and highly understudied ancient predator and is one of the largest living Dasyatids (whip-rays) family of fishes left on the planet.

The Giant Freshwater Stingray belongs to the class Chondrichthyes, which includes all 850 species of sharks, rays, skates, and chimaeras. These fishes have cruised the oceans since the Paleozoic era.

The basic dorsoventrally compressed body plan of the ray is thought to have originated during the Jurassic period, approximately 100 Mya. This design, coupled with the absence of a swim bladder and powerful jaws designed for crushing hard shells of mollusks such as clams and muscles, has made the ray the successful benthic predator it is today. The Giant freshwater stingray is found throughout the great river systems of Thailand in freshwater and estuarine enviroments and is possibly the largest freshwater fish on the planet.

This mighty Paleozoic predator is easily identifiable due to its immense rounded disc-like shape measuring upto three metres in width with a prominent snout tip and whip-like tail. Within the central section of the disc the main body of the ray is located housing the fish’s internal organs and in some specimens displaying the endoskeleton of the creature.

The Giant freshwater stingray is a cartilaginous fish with the creature’s skeleton being entirely composed of pure cartilage.

At the front of the pronounced body section small protruding ‘periscope’ eyes are located allowing it a limited field of vision of the water column above whilst buried in the muddy riverbed. Behind the eyes is the spiracle area often referred to as the ‘sixth gill’ which acts as a primitive type of snorkel. This adaptation allows them to breathe more easily while they are hiding in the substrate.

The Giant Freshwater Stingray has a dark brown surface on its upper/dorsal side with a highly abrasive textured skin covered in placoid scales, the tiny tooth-like structures that protect the skin of elasmobranchs and give it a sandpaper-like texture. The creature’s underside is of a very smooth nature characteristically white in colour with a grey to brown colouration around the edges. A huge cavernous mouth is located on the underside lined with highly abrasive crushing pads. Jelly-filled sensory pores “Ampullae of Lorenzini”, located on the skin around the nose and mouth on the underside of the disc, are present in most elasmobranchs and allow sharks and rays to detect minute electric fields generated by living things. This is especially useful for freshwater stingrays because it helps them to hunt down prey that might be buried in the riverbed or hiding in murky water. In addition two rows of five gill slits are located on the underside/ventral side of these prehistoric predatory giants.

The Giant Freshwater Stingray is armed with two venomous barbs located close to the base of its tail which have two components: the sharp inner barb used for piercing, and a thin sheath surrounding it that contains the venom. When the spine is deployed, the barb pierces the venom sac along with the victim’s skin, and the poisonous slime is introduced into the wound. The barb is extremely sharp (it has been known penetrate bone), and it operates under the same principle as an arrowhead– it slides into flesh fairly easily, but the serrated edges make it very difficult and painful to extract. The tail is very flexible and can move in any direction within a split second, inflicting serious damage. In addition to causing great pain, the venom contains enzymes that cause tissue death. Similarly to the teeth or dorsal spines of a shark, stingray spines are thought to have originated from placoid scales, the tiny tooth-like structures that protect the skin of elasmobranchs and give it a sandpaper-like texture. Placoid scales, just like shark teeth, are lost and re-grown on a regular basis.

Determining the sex of these mighty living fossils is a relatively easy exercise with male specimens displaying obvious genitalia called claspers similar to those of a shark at the base of the tail. Female specimens are easily distinguishable by an absence of genitalia in this region.

The Giant Freshwater stingray gives birth to live young in small numbers (thought to be three or four) which are born perfectly formed.

Recently whilst filming with the National Geographic society the Fishsiam team captured a Giant Freshwater Stingray which was observed to be heavily pregnant.

During a short examination at the riverside the large female stingray gave birth to a live newborn measuring a mere 34cm’s.

This astounding natural world first was captured on film in what we believe to be the first recorded Giant Freshwater Stingray birth ever witnessed in a wild and natural environment.

The mother and infant were promptly released back to the Ban Pakong River after scientific data and photography were completed.

Giant Freshwater Stingray research

Whilst fishing at both the Ban Pakong and Maeklong Rivers the Fishsiam team has been gathering valuable scientific data concerning Himantura Chaophraya. Every specimen captured by the team is accurately measured in addition the sex and condition of each fish is recorded. The location of each capture is also recorded giving a helpful insight into the fish’s distribution throughout the river systems. This information is crucial for further research concerning population densities of these amazing creatures.

A research program has been proposed by Dr.Zeb Hogan from the National Geographic society and mega fish project in which the Fishsiam team would partake in the tagging and monitoring of Giant Freshwater Stingray. Using radio transceivers placed at various parts of these large tidal rivers, it has been proposed that radio tracking tags be placed on Giant Freshwater Stingray in an attempt to track the ray’s movements throughout the river systems.

The radio tagging of Giant Freshwater Stingray will be a revolutionary step to gaining a huge insight into this most obscure and understudied species and possibly reveal whether these underwater monsters are true freshwater giants or in fact venture into marine enviroments as previously suggested. The proposed research program is subject to governmental approval by the Royal Dept of Thai fisheries.

The Fishsiam team whilst fishing for this mighty prehistoric predatory species uses the strongest of equipment in the capture of Giant Freshwater Stingray.

Epic battles lasting several hours are a regular occurrence when fishing for Giant Freshwater Stingray often requiring numerous anglers to successfully land these massive predators.

When a fish is brought alongside the boat the creatures deadly tail is tightly grasped below the barb before the barb is tightly wrapped with cloth rendering the barb harmless. The fish is then taken to shallower water where it is allowed a short period to recuperate at the rivers edge. The capture of a Giant Freshwater Stingray requires the participation of several anglers/guides to safely and harmlessly secure and transport these creatures to the riverside.

All Giant Freshwater Stingray captured by the Fishsiam team are safely released unharmed after the recording of scientific data and photography are completed.

The conservation minded Fishsiam team under the guidance of owner Wuttichai ‘Boy’ Khuensuwan have the utmost respect for these creatures and ensure that all steps are taken concerning the welfare and safety of these ‘Living Fossil’s’.

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