River Dolphins of No Return
by Robin Meadows
QUICK—Let’s test your dolphin knowledge
by playing “two truths and a lie.” Which
of the following three statements is not true?
- Dolphins are related to hippopotamuses.
- Dolphins swim in rainforests.
- Dolphins sing long, complicated songs.
If you guessed that the last statement is wrong, you’re right. Whales sing—dolphins make clicks and whistles. As for how hippos and dolphins are related, see the sidebar “The Dolphin–Hippo Connection”.
Surprised that dolphins swim in rainforests? I was too. But it’s true: Dolphins live in the Amazon River and, when it floods the surrounding forest, they swim among the submerged tree trunks, hunting fish that eat the fruit and seeds on the inundated forest floor.
Worldwide, there are four types of dolphins that live only in rivers. The Amazon River dolphin (Inia geoffrensis) is the only one that is still plentiful. The other three live in Asian river systems and all of them are endangered: The Yangtze River dolphin (Lipotes vexillifer) is almost extinct, and the Indus and Ganges river dolphins (Platanista minor and P. gangetica, respectively) are down to about a thousand and a few thousand, respectively.
While there is still time to save the Indus and Ganges river dolphins, they face many of the same threats that are driving the Yangtze River dolphin toward extinction. “Asia’s large rivers have been ravaged and impoverished by human overuse and misuse, leading to enormous losses of wildlife,” says Randall Reeves, chairman of the World Conservation Union’s (IUCN) Cetacean Specialist Group. Likewise, the Amazon River dolphin is vulnerable because South America’s rivers are being used more and more as the human population grows.
Despite their far-flung distribution, these four river dolphins have a lot in common. They generally look alike and prefer the same types of habitats in rivers. One of their most striking features is a long, slender snout, which is lined with as many as 150 sharp, pointy teeth. River dolphins also have small eyes, and those that live in the Indus and Ganges Rivers are essentially blind because their eyes lack lenses. River dolphins don’t need eyesight to navigate and hunt because they have well-developed sonar systems, allowing them to live in water so turbid that they couldn’t see anyway.
Compared to their streamlined marine cousins, river dolphins are stockier and have tiny dorsal fins and broad, paddle-like flippers and flukes. They are also slower and typically swim at about one mile per hour, which is roughly a fifth of the cruising speed of marine dolphins. River dolphins have traded speed for far greater maneuverability, allowing them to swim in shallow, narrow waterways and so make the most of their riverine habitat. Notably, the Indus and Ganges river dolphins can swim in water that is only a foot deep.
Given the choice, however, river dolphins prefer deeper water and particularly favor counter-current pools, or eddies, that provide refuge from the swift currents of rivers. “They live in a constant current so they take advantage of places like bends and confluences of rivers where the flow is slower,” says Reeves. Another attraction of counter-current pools is that they are rich in fish, the dolphins’ primary prey. “Counter-current areas are biological ‘hotspots’ within large Asian rivers,” he says.
Similarities notwithstanding, genetic evidence suggests that each river dolphin species evolved independently. River dolphins are far more primitive than modern marine dolphins, and the Indus and Ganges river dolphins are among the most primitive mammals alive today. According to their 2001 paper in The Royal Society Proceedings: Biological Sciences, Healy Hamilton and colleagues calculated that river dolphins began evolving at least 15 million years ago.
During this time, sea levels were globally high and the scientists suggest that the timing of these two events was no coincidence. The high seas flooded low-lying regions of continents, forming extensive inland seas, and the story goes that ancient marine dolphins moved into these inland seas and then remained in—and adapted to—rivers when sea levels fell again. Fossil evidence shows that river dolphins were once more widespread than they are today, concentrated in relatively warm coastal regions in North America, in what is now southern California, Florida, and Maryland, as well as in Argentina.
The very thing that makes these dolphins so fascinating—the fact that they live in rivers—is also their biggest problem. Adapted to live only in rivers, river dolphins have nowhere else to go when their habitat is destroyed or degraded to control flooding, provide irrigation water and hydropower, or facilitate boat traffic. “The extreme specialization of the species puts them at great risk—by accident of birth, they’re in trouble,” says Reeves.
The main threats to river dolphins include: dams, which fragment their habitats and deplete the water; fishing, which often accidentally kills dolphins too; boats, which collide with and kill dolphins and make noise that can interfere with their sonar; and pollution, which degrades the water the dolphins live in. “They all face similar threats. Living in rivers puts them in such close proximity to people because rivers are so heavily used by people,” says Gill Braulik, who like Reeves is in the World Conservation Union’s Cetacean Specialist Group.
Yangtze River Dolphin: The
Baiji
The Yangtze River dolphin is called the baiji, which
means “white dolphin.” An estimated 5,000
once lived in the middle and lower reaches of the river
from its mouth at Shanghai to Three Gorges. Traditionally
revered as a river goddess, the baiji’s numbers
dropped dramatically in the late 1950s, as it was hunted
for food and hides during China’s “Great
Leap Forward.” There was even a factory specializing
in baiji skin gloves and handbags, but it soon closed
because the dolphins became too scarce.
The baiji has been legally protected since the 1980s, and three parts of the Yangtze were designated reserves. Even so, the species continued to decline steadily from about 400 individuals in 1984 to 200 in 1990. In 1995, biologists tried to catch the remaining baiji and put them in a 12-mile-long reserve in an oxbow near Wuhan, in central China, where they would have been relatively easy to protect. But in six months of searching, the biologists saw only seven of the dolphins and managed to catch only one. Today, there are probably fewer than 50 left, making the baiji one of the most endangered species in the world.
The most immediate threats to the baiji include deaths from boat collisions, underwater blasting during harbor construction, and three illegal—but widely used—fishing methods: electrofishing, explosives fishing, and rolling hooks. The latter method entails the use of tens of thousands of long lines, each set with thousands of hooks to catch larger fish that inhabit the river bottom.
The baiji shares its habitat with hundreds of millions
of people. At nearly 4,000 miles, the Yangtze is the
third-longest river in the world and its basin is home
to well more than a tenth of the people in the world.
The Yangtze is used extensively for agriculture, industry,
and transportation. In 1990, boat traffic rates in the
river’s lower reaches exceeded one per minute.
In addition, most sewage and industrial and agricultural
wastewater are discharged directly into the river without
treatment. “The degradation of the Yangtze continues
unabated,” says Reeves.
The baiji has been largely written off by conservationists, who expect it to die out within a few decades despite their hard work to save it. “The baiji’s imminent extinction is a national tragedy and an international disgrace,” says Reeves.
Even so, some good may come of the baiji’s all-but-certain demise. “The fate of the baiji is an early warning system for other river dolphins,” says Braulik of the Cetacean Specialist Group.
Indus River Dolphin: The Bhulan
Braulik recently surveyed Pakistan’s Indus River
dolphin, which is called the bhulan, and he estimates
that there are about 1,100 left. “Pakistan is
starting from a better position than China—the
numbers are high enough that we could actually do something
to help them,” she says.
One reason for the bhulan’s relative abundance is that more than 95 percent of Pakistan’s people are Muslim, and Islamic law forbids consumption of dolphin meat. “This probably helps explain why the Indus dolphin has survived as long as it has,” says Reeves. Other reasons include that the Indus has no large cities on its banks, is not heavily fished, and has few motorboats, because most goods are transported on roads.
Despite these factors in its favor, the bhulan faces a formidable threat. Its habitat has shrunk to a fifth of its historic size, which once stretched about 2,000 miles from the mouth of the Indus to the Himalayan foothills and included four huge Indus tributaries. The dolphin’s competition is the intensive agriculture in the arid Indus plains that has driven construction of the largest continuous irrigation system in the world. Since 1932, Pakistan has built about 25 dams and barrages, which are gated dams that divert water into irrigation canals, and more than two-thirds of the Indus’ flow is now diverted.“For almost half of the year, no water reaches the delta,” says Braulik. “The river becomes a sea of sand.”
The barrages keep the bhulan from traveling freely, isolating populations from one another. Dolphin populations trapped upstream of barrages typically die out, and today only a few of the remaining populations are big enough to have a chance of surviving, with the largest estimated at 600 and the smallest at only 70.
Bhulans also get trapped in irrigation channels. They swim through the open gates during the monsoon season only to become stranded as the water levels drop during the dry season. The dolphins can swim as far as 90 miles down tiny canals through the desert. Braulik estimates that irrigation canals trap 12 to 15 bhulans per year from the largest population, which may be more than it can sustain. The local wildlife department has recently been rescuing the bhulan from canals and transporting them back to the Indus. “You put them on a stretcher, protect them from the sun, and use sponges to keep their skin wet. Transport can take as much as seven hours because we often have to travel on unpaved roads through desert,” says Braulik.
Another positive development for the bhulan is ecotourism along the Indus. A local nongovernment organization called the Adventure Foundation of Pakistan is sponsoring boat tours down the river to see bhulan and other wildlife, including cranes, flamingos, otters, and turtles. These tours are led by fishing families who live on the river and encourage other local fishermen to release bhulan that get caught in their nets.
Ultimately, however, the bhulan’s survival will depend on the animals’ having enough water to live in. Braulik would like to see a minimum amount of water allocated to the Indus for the dolphins, but acknowledges that this may be difficult. “There is just not enough water to go around in Pakistan. Any river water that reaches the sea is viewed as wasted, so it’s hard to do anything,” she says. In the meantime, the best that conservationists can do is to continue monitoring the species to see if the population drops further—and, of course, to try to do something about it if it does.
Ganges River Dolphin: The Susu
Estimated to number roughly a few thousand, the Ganges
River dolphin or susu is doing slightly better than
the closely related bhulan. But this does not mean that
the threats to the susu are any less severe. Rather,
this species is more abundant because its habitat is
far more extensive. Susus are still found in much of
their historical range in the Ganges–Brahmaputra–Megna
River system in India, Bangladesh, and Nepal, and the
Karnaphuli River system in Bangladesh.
Like the baiji, the susu faces many threats. Among the worst are dams, fishing-related deaths, and hunting. About 50 dams and barrages have fragmented the susu into perhaps 20 populations. As in Pakistan, “groups of dolphins upstream of dams and barrages have either disappeared or declined with little prospect of recovery,” says Reeves.
The susu is all but gone from Nepal, where barrages have essentially eliminated the dolphins from three of the four rivers where they once lived. Today, only the Karnali River has a population large enough to have a chance of surviving, and its prospects are not good. One reason is that yet another dam is planned, this one on the Karnali itself. “We believe that this population will soon go extinct in the absence of conservation action,” wrote Indian zoologist Ravindra Sinha and his colleagues in a 2000 IUCN report called “Biology and Conservation on Freshwater Cetaceans in Asia.”
In India and Bangladesh, the susu also is threatened by heavy gillnet fishing and hunting. Gillnet fishing both depletes the species’ prey and kills the dolphins directly. Dolphins have a hard time detecting the fine nylon gillnets and, once ensnared, cannot break free, so they become entangled and soon drown. Furthermore, although the susu is legally protected from deliberate killing throughout its range, fishermen in some parts of India and Bangladesh still hunt the dolphins for their oil, which they mix with goat fat to create a concoction used to lure fish.
Without active protection, the susu is likely to go the way of the baiji.“The greatest lesson of the baiji may be that early conservation action is required before a [species] has reached an irreversible threshold of decline,” wrote Sinha and his colleagues.
As a first step, they advocate strengthening the susu’s protection in its only reserve. A 30-mile segment of the Ganges in Bihar, a province in northwest India, was declared a sanctuary in 1991, but fishermen still hunt susu and accidentally kill them in fishing nets there. Sinha and others are working to “transform the sanctuary from one that exists only on paper to one that provides effective protection to dolphins.”
Amazon River Dolphin: The Boto
The Amazon River dolphin is called the boto or the pink
river dolphin—and some of them are actually bright
pink. Their numbers are unknown, but the boto has an
enormous range in the Amazon and Orinoco river basins,
which together encompass 2.7 million square miles. The
boto enjoys vast stretches of rivers that remain free
of dams and pollution, and is found all along the rivers
from the deltas to the headwaters, where impassable
waterfalls limit its range.
But things are changing in the Amazon. More people are settling along the rivers as the human population grows, making the boto increasingly vulnerable to the threats that have endangered the Asian river dolphins.
The boto was traditionally protected by legends that it had supernatural powers. Although botos are quite playful—they grasp fishermen’s paddles, rub against canoes, and throw sticks—local people were afraid of them. “Many river-dwelling people in Peru regard the animal with superstitious dread, fearing that handling it will precipitate a long series of retributive consequences for them and their families,” says Reeves. “Dolphin hunting is in some sense taboo in much of Amazonia.”
Unfortunately for the boto, these beliefs are disappearing and recent settlers in the Amazon often see the dolphins as competitors for fish. Local people report that some fishermen now poison botos by tossing them fish injected with an agricultural insecticide called methyl parathion.Accidental boto deaths are also rising as nylon-gillnet use and dynamite fishing become more widespread. Pollution is increasing as well, and the milk of female botos in the upper Amazon contains pesticides and mercury.
Perhaps worst of all, the Amazon is likely to get more dams. There are plans to build hydroelectric dams on many Amazon tributaries and on the Orinoco, and to build a system of dams and locks on the Orinoco that would make the river navigable year-round.
Conserving River Dolphins
Despite the dangers river dolphins face, hope remains
for those in the Amazon, Indus, and Ganges. One way
of conserving river dolphins is to establish meaningful
reserves by setting aside areas the dolphins favor and
enforcing bans on harmful fishing methods and boat traffic.
Another way is to improve water quality by treating
industrial waste and sewage and decreasing agricultural
pesticide runoff.
Conservationists also recommend making dams and other water developments more environmentally friendly. This might actually happen. Thanks to the growing awareness of the considerable environmental costs of dams, the World Bank, which funds many large dam projects, now stresses that water-development projects should include components to conserve biodiversity. There are two ways to make dams less harmful to river dolphins. One is to build them near the headwaters, which leaves longer stretches of uninterrupted river habitat. The other way is to concentrate the dams on one river, which leaves other rivers free of them altogether.
Most important, people need to realize that there is a limit to what rivers can provide. “Our freshwater resources are exhaustible and a river’s capacity for serving human needs is finite,” says Reeves. That also goes for serving the needs of the dolphins as well as the many other creatures that live in rivers.
—Robin Meadows is a freelance science writer based
in California and a contributing editor to ZooGoer.
ZooGoer
32(5) 2003. Copyright 2003 Friends of the National Zoo.
All rights reserved.
