Glyphis gangeticus

Geographic Range

Glyphis gangeticus (Ganges river shark) is found throughout and within the vicinity of multiple South/Southeast Asian river systems. They have been found in the Ganges delta system, the Hooghly River, freshwater systems within the West Bengal region of India, and in marine waters surrounding the Indian subcontinent and the Indonesian archipelago. Notably, Ganges river sharks are the only shark species that is native to the Ganges delta, although the similar-looking Carcharhinus leucas (bull shark) has also been found in the area.

• Biogeographic Regions
• oriental oriental
  • native native
• indian ocean
  • native native

Habitat

Ganges river sharks are thought to reside within both freshwater river and shallow marine habitats, although there is some debate regarding which environment they spend more time in, or whether they are a truly euryhaline species at all. Regardless, they are thought to be able to withstand the rather turbid waters that occur in the broader Ganges region.

• Habitat Regions
• tropical tropical
• saltwater or marine saltwater or marine
• freshwater freshwater

• Aquatic Biomes
• rivers and streams
• coastal coastal
• brackish water brackish water

• Other Habitat Features
• estuarine estuarine

Physical Description

Ganges river sharks have a fairly characteristic stout-bodied selachimorphan appearance. They have countershading coloration, with a dark gray top half and a whiter lower half of the body. Ganges river sharks can grow quite large, being found at lengths of up to 266 cm, but average at about 178 cm by maturity. Based on the largest discoveries and accounts of related species, such as bull sharks, females are thought to grow larger than males. Reliable records of their weight could not be located in the literature. Other identifying features include that they have short snouts, a long, hooked caudal fin, narrow teeth on their lower jaw, and wider serrated teeth on their upper jaw. While data specifically relating to body temperature regulation in Glyphis gangeticus is seemingly unavailable, sharks as a whole are known to be ectothermic.

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger

Development

Not much is known about the life history of Ganges river sharks, but other river shark species within the genus Glyphis (river sharks) are understood to have a slow growth rate, lengthy gestation periods, low fecundity, and delayed time to maturity. River sharks in general, though, are not very well documented in this regard.

Reproduction

No documentation of the mating system(s) practiced by Ganges river sharks or by the Glyphis genus as a whole could be located, but species within the broader Carcharhinidae family (requiem sharks) are known to practice polygamy, in which individuals have more than one mate, so it could be reasonably assumed that Ganges river sharks do as well.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Little is known about the specific reproduction habits of Glyphis gangeticus , but they are a viviparous species that presumably utilize a yolk-sac placenta and maintain a slow reproduction rate with small litter sizes. Specific details regarding gestation period/frequency, breeding season, and litter sizes are unknown for river sharks. There is evidence to suggest that sharks within the Glyphis genus, similarly to bull sharks, spend most of their mature lives within marine environments, but return to freshwater rivers for reproduction, though. This behavior may be beneficial in that there is then less threat of predation on juvenile sharks. Additionally, other river sharks are thought to give birth during the fall, preceding the wet season. Like all other shark species, males have claspers to transfer sperm into females for internal fertilization.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• sexual sexual
• fertilization fertilization
  • internal internal
• viviparous viviparous

There has been no documentation of parental care by Ganges river sharks or other members of the Glyphis genus after offspring are birthed. Although, it is expected that no postnatal care is practiced, as it is an absent behavior in other viviparous Carcharhinids, which see fully-developed, independent offspring upon parturition.

• Parental Investment
• no parental involvement
• precocial precocial

Lifespan/Longevity

The lifespan of Ganges river sharks is unknown, as are concrete lifespans of other species within the Glyphis genus. However, the related and relatively similar-sized, euryhaline bull shark has been found to reach ages of 29-34 years old, with an average lifespan of roughly 12-16 years, so this is potentially close to the longevity of Ganges river sharks as well.

Behavior

Little is known about specific behaviors associated with Ganges river sharks. Based on other carcharinids , they most likely utilize ram ventilation for respiration, but it is possible that they also have the ability to breathe while stationary via buccal pumping. Ganges river sharks are understood to move through the water column via body and tail undulation. They appear to be solitary, but it is unknown whether or not they exhibit any degree of social behavior.

• Key Behaviors
• natatorial natatorial
• motile motile

Home Range

Glyphis glyphis (speartooth sharks) have been noted to annually migrate between salinities, with a movement into more saline environments having been found to occur during January and February, where they would remain until at least late March. It is possible that Ganges river sharks perform similar migratory actions.

Communication and Perception

Details regarding the communication ability of Ganges river sharks are not known, but they presumably utilize some form of visual cuing to communicate with conspecifics. Regarding perception, similarly, there is little information about specific abilities of the Ganges river shark, but, like all sharks, they have an additional sensory system in electroreceptors located on their snout that detect weak electrical fields within the surrounding water, which is thought to be primarily used for prey detection and navigation.

• Communication Channels
• visual visual

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical
• electric electric

Food Habits

Ganges river sharks are thought to mainly feed on the variety of medium-bodied bony fish that live within their distribution, but their preferred prey items are unknown. Speartooth tooth sharks of the same genus have also been found to consume stingrays, at least on occasion.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore

• Animal Foods
• fish

Predation

There are no known predators of Ganges river sharks. However, it is theoretically possible that bull sharks, as large euryhaline predators whose distribution overlaps with that of Ganges river sharks, occasionally prey on juveniles of the species.

Ecosystem Roles

Ganges river sharks act as predators of other aquatic organisms, and possibly are prey items themselves as juveniles, but their particular niche and importance within their ecosystem is unknown. Although, judging by their size and anatomy, they are likely to be apex predators, occupying the top trophic level as a tertiary consumer.

Economic Importance for Humans: Positive

Ganges river sharks are of negligible economic importance, but in rare occasions they are sold, generally illegally or accidentally, in fish markets for their meat, fins, and/or jaw bones.

• Positive Impacts
• food food
• body parts are source of valuable material

Economic Importance for Humans: Negative

Ganges river sharks are not known to have any negative economic impact on humans.

Conservation Status

As of 2021, Glyphis gangeticus is labelled as a critically endangered species on the IUCN Red List due to its extreme rarity in terms of records and its perceived susceptibility to environmental degradation/modification and overharvesting, whether intentionally or as bycatch. Since 2001, the harvesting of Ganges river sharks has been illegal in India, but the effectiveness of this law is uncertain.

Additional Links

Encyclopedia of Life

Contributors

Sam Dunphy-Miller (author), Texas State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

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