Irrawaddy River Shark

The Ganges shark, as its name suggests, is largely restricted to the rivers of eastern and northeastern India, particularly the Hooghly River of West Bengal, and the Ganges, Brahmaputra, and Mahanadi in Bihar, Assam, and Odisha, respectively. It is typically found in the middle to lower reaches of a river. One found in 2018 in a Mumbai fish market may have come from somewhere along the banks of the Arabian Sea. In theory, G. gangeticus could occur in shallow marine estuaries; however, no marine records of the species have been verified to date. Originally, the species was assigned a wide range in the Indo-West Pacific, but this was found to be mostly based on other species of requiem sharks, particularly members of the genus Carcharhinus. Most literature records and specimens labelled as this species are in fact bull sharks (Carcharhinus leucas) or other carcharhinid species. An extensive 10-year search produced only a few specimens, caught in 1996 in the Ganges River.

G. gangeticus is known to inhabit only freshwater, inshore marine, and estuarine systems in the lower reaches of the Ganges-Hooghly River system. Their feeding habits are mostly unknown. The shark's small eyes and slender teeth suggest that it is primarily a fish-eater and is adapted to turbid water. With such limited visibility typical of many tropical rivers and estuaries, other senses − such as hearing, smell, and electroreception − are likely used for predation. Because its eyes are tilted towards its back rather than to the sides or bottom (as is the case in most carcharhinids), the shark may swim along the bottom and scan the water above it for potential prey back-lit by the sun. However, in the Bay of Bengal, G. gangeticus was found to feed heavily on dasyatid stingrays, which spend much of their time on the bottom.

Reproduction. It is probably viviparous, with a yolk-sac placenta (speculation through analogy to related species of carcharhinids). The litter size and gestation period are unknown. However, their life history cycle is probably similar to other river sharks, characterized by long gestation, slow growth, delayed maturity, and small litter size. These factors make the Ganges shark populations vulnerable to even relatively low levels of exploitation, such as sport angling or gill netting.

Possibility of migration. Some researchers consider G. …