A Hooghly head‐scratcher

Abstract

Here’s one for you: when is a critically endangered, maneating, freshwater shark a common, fish-eating, marine creature that never bit anyone? Answer: when it’s a Ganges shark (Glyphis gangeticus) (Figure 1). But don’t let that name fool you. While it might turn up anywhere from Pakistan to Borneo, the last place to look for it is in the Ganges. If you like your elasmobranchs enigmatic, you’ve come to the right place! The Ganges shark. flickr.com/Biodiversity Heritage Library In Volume 1 of his vast work, The Fishes of India (1878; London, UK: William Dawson and Sons Ltd), pioneering 19th-century ichthyologist Francis Day wrote, “This is one of the most ferocious of Indian sharks, and frequently attacks bathers even in the Hooghly at Calcutta, where it is so dreaded that a reward is offered for each that is captured”. Certainly, shark attacks in the Bay of Bengal – into which the Ganges flows via its many distributaries, including the Hooghly River – were once not uncommon. Until some 200 years ago, people would gather on Sagar Island where the tidal Hooghly meets the salty Indian Ocean, for grim festivals in January and November. There, around the full moon, elderly men and women would walk into the murky water with the purpose of being devoured. And devoured they often were. Some families would even cast their fifth-born child to the sharks as a sacrifice to the Ganges. Harrowing accounts of the practice (see Travels of Fray Sebastien Manrique 1629–1643, Vol 1, 2016; Abingdon, UK: Routeledge, or Papers etc: Third Part, Vol IX, 1812–1813; London, UK: East India Company), which was frowned upon by the greater population and sanctioned by no religious code, eventually led to its prohibition – at least the part concerning children. But were the executioners Ganges sharks? While these fish can reach well over 2.5 m in length, many authors highlight that their slender teeth are far more suited to grabbing fish than humans. A much more likely culprit is the similar-looking bull shark (Carcharhinus leucas), which has all the right equipment. Day also wrote of the Ganges shark “ascending rivers to above tidal influence”, an assertion last backed up in 2001 by some jaws collected 84 km upstream from the mouth of the Hooghly. And certainly, you don’t have to work hard to gather a bunch of modern references that describe this fish as a true freshwater/estuarine shark, with some claiming there to be no marine records for the species at all. One author even cites it having overcome rapids to inhabit the upper reaches of the Agusan River in the Philippines, 150 miles from the sea. But wouldn’t the ability to enter the ocean proper help explain how the Ganges shark got to the Philippines? Or to Sri Lanka, where one might also have turned up? And wouldn’t a seafaring capability also help explain the genetic evidence identifying a shark that inhabits the lower reaches of the Kinabatangan River in Borneo as G gangeticus? Swimming hard against the freshwater-lifestyle current, one well-known ichthyologist cites the creature as an entirely brackish water/marine animal. In 2006, Tyson Roberts reported how, after years of fieldwork, he was unable to find any record of the Ganges shark in the Ganges itself, or in any body of freshwater he examined from India to Myanmar, “debunking the mythology of the Gangetic freshwater shark” (Nat Hist Bull Siam Soc 2006; 54: 261–78). Neither did he find any freshwater fisherman, fisheries biologist, or riverbank fishmonger who had seen one. He even went on to show that the first description of the fish by Augustin Lamare-Picquot as a beast of the Ganges was probably due to a confusion of field notes and errors in translation. In contrast, Roberts found plenty of Ganges sharks hauled in by sea fishermen; he even cited them as the species of large shark most commonly captured by the villagers of Sittwe in Myanmar. It is “a common groundshark in the Bay of Bengal”, he declared, “rather than any endangered freshwater shark of the Ganges”. And yet the Ganges shark is still generally regarded as extremely rare, with its numbers in decline. The IUCN records it as critically endangered, and when one turns up at a fish market it’s enough to get ichthyologists dashing for their cameras. Not something you’d expect if you had first read Roberts’ paper, which emphatically states that “there is no evidence of [a] historical decline in the range of the species or in its population numbers. It is not critically endangered or even threatened”. Of course, the fortunes of the Ganges shark may have changed since Roberts’ paper put the cat among the Hooghly pigeons, but even in 2006 it was generally considered to be very scarce. So there you have it. The Ganges shark: a rare, deadly, freshwater fish found only in marine/brackish habitats, commonly in the Bay of Bengal, that never hurt a fly, and with a “Hooghly” inappropriate common name. Got that everyone? Good! I’m glad we got that cleared up.