River Dolphins, and the Goddess of the Yangtze

Nathaniel Stickman |

River dolphins in a small assemblage — only a few — come up shyly, grazing the surface of the opaque river. And, as quickly, they descend. One raises a flipper and, without a splash, slips beneath the surface again to a shelter of silt. A human paddling along nearby cannot hear them now, but, as the dolphins spread beneath the turbid water, they click and whistle in parting.

Despite obvious similarities, river dolphins actually consist of three distinct phylogenic families. Three species of Inia live in South American rivers; nearby, Pontoporia blainvillei lives in the coastal waters and estuaries of Argentina, Brazil, and Uruguay; two species of Platanista, meanwhile, span Bangladesh, India, and Nepal, one living in the Ganges and the other in the Indus River.1 2 Each family likely broke away from its marine-dwelling relatives — such as the recognizable bottlenose dolphin — long ago and has since evolved on its own path. To put that in perspective, each river dolphin family is about as closely related to the others as their marine namesakes are to narwals.1 Most marine dolphins are, by contrast, species of a single family, Delphinidae, and are thus closely related to each other.3

But, for being so far apart geographically and phylogenically, the Inia and Platanista families have an uncanny resemblance to each other. Living in similar habitats — rivers, where visibility is low and shoulder room scarce — likely contributed to the families' similarities.4 Both have long beaks, apt for river hunting, as well as flexible necks and subtle dorsal fins that make travel in tight river spaces easier.5 6 These river dolphins also have large melons — the forehead regions used in echolocation — as they have to rely almost entirely on echolocation over sight to navigate murky rivers' twisting, obstacle-laden routes. Because of this, river dolphins are especially susceptible to loud, continuous noises — like motorboats — echoing through their river spaces.

The similar fluvial habitats also mark Inia and Platanista behavior. A boto — a common name for dolphins in the Inia family — usually has an almost solitary life, with the only close social relationship being between mothers and their children.5 Similarly, the Ganges and Indus River dolphins — those in the Platanista family — live almost solitary lives.6 Dolphins of either family may form loose groups, but those are occasional and contrast the highly-social pods typical of marine dolphins. The close quarters of their waterways probably contribute to river dolphins keeping distance between their kin, allowing each dolphin its own space for hunting. River dolphins are also generally less ostentatious than marine dolphins, which, combined with their infrequent time socializing in groups, has made it difficult for humans to track and study them extensively. Canoers in South America may see botos playfully tossing sticks out of the water and even prankishly tugging at oars, but their overall reclusiveness makes such antics infrequent and tends to send them back beneath the water quickly, spreading away from researchers' reach.5 7

Contrasting the similarities in Inia and Platanista dolphins, a franciscana — a common name for Pontoporia blainvillei — more closely resembles its marine relatives, perhaps because, though it has a river dolphin ancestry, it has begun to adapt to its marine habitat on the South American coasts.8 For instance, franciscana has a pronounced dorsal fin, something it shares with none of the other river dolphins, and lives in pods like marine dolphins, even comparable in size. While franciscana has maintained the long beak typical of river dolphins, its melon has shrunk, making its profile easier to confuse with a bottlenose than a Ganges River dolphin.

River dolphins in general, though, have all retained at least some similarities to their marine relatives. Aside from the obvious physical similarities, river dolphins also share the loquaciousness humans have come to associate with marine dolphins. While humans had long thought that river dolphins were not as adept communicators as ocean dolphins, a group of researchers recently sought to challenge that notion.7 The researchers followed a group of botos around to listen in on their conversations, finding their participants among a group of more human-friendly botos that regularly visited a market in Northern Brazil. The botos conversed not only in abundance, but elegantly, with a range of sounds suggesting capabilities perhaps rivaling marine dolphins.

That study is one of the few deep observations of river dolphin behavior in the wild. It benefitted from a group of botos more familiar with humans, but most river dolphins are elusive, especially around humans, and that has made it difficult for researchers to better understand what river dolphins' lives are like in the wild. Compounding that, river dolphins have become progressively more scarce. Each family of river dolphin has seen population declines, and botos and the Ganges and Indus River dolphins are considered endangered; another river dolphin species, the last of its family, had been similarly endangered before going extinct only 13 years ago.9 10 (More about this species further on.) Human civilizations have long relied on rivers for transportation and fishing, and river dolphins have had to share those spaces; as human civilizations have grown, however, river dolphins have progressively been crowded out.11 River dolphins face not only food competition from human fishing, but accidental capture or injury by aggressive fishing practices. Motorboats have proven a particular detriment, too, as the constant noise threatens to blind and confuse river dolphins anywhere near the ever-expanding boat traffic.

Until recently, there had been four families of river dolphins in the world. The fourth, Lipotes, had been represented by one species, the baiji dolphin (Lipotes vexillifer, “left-behind flag-bearer”), which primarily lived in China’s Yangtze river.12 The dolphin was known in human folklore as the “Goddess of the Yangtze,” legendary for her beauty. Starting in the 1950s, the baiji dolphin population was rapidly upended by human activity in the Yangtze — from the noise pollution to indiscriminate fishing practices. Around 1980, estimates had the population down to approximately 400 individuals; by 1999, the population had fallen to 13. The measures taken to curb the decline were late and insufficient — the baiji’s waterway was of too much “economic importance” — and so people carried on. The Goddess of the Yangtze was declared likely extinct after an expedition in December 2006 had been unable to find any evidence of a single surviving baiji in the great river.

Botos and the Ganges and Indus River dolphins seem poised dangerously near the same precipice over which baiji was once gradually pushed. To help the river dolphins that remain, humans will need to do more than just abdicate certain behaviors. They will, instead, need to change the nature of their interactions with the environments in which these dolphins live, which would have broader implications for the human products that pass through these waterways. Still, organizations like the World Wildlife Fund strive for such change, and humans retain the ability and opportunity to make river dolphins' homes safe and hospitable for them.9

The splash image is Michelle Bender, Amazon River Dolphin, May 10, 2012, https://commons.wikimedia.org/wiki/File:Amazon_river_dolphin.jpg. It is distributed under the Creative Commons Attribution-Share Alike 2.0 Generic license.

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  2. “River Dolphins,” Whale and Dolphin Conservation, accessed April 12, 2020, https://us.whales.org/river-dolphins/. ↩︎

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  8. Stacey Collerone, “Pontoporia Blainvillei: Franciscana,” Animal Diversity Web, accessed April 12, 2020, https://animaldiversity.org/accounts/Pontoporia_blainvillei/. ↩︎

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