(Get a genetics overview.)
Bolivian river dolphins—especially females—also look different from their Amazon relatives.
In contrast to Amazon river dolphins, which are considered "pink," the members of this new species are a pale gray. They also have more teeth, smaller heads, and smaller bodies.
Ruiz-Garcia also considers the Bolivian species to be chubbier and rounder.
The latest genetic studies on the newly declared species allow "a very clear reconstruction of evolutionary history," said Fernando Trujillo, scientific director of Colombia's Fundación Omacha and the leader of South America's first river-dolphin census in 2007.
The River Dolphin Monitoring initiative for South America counted 3,188 river dolphins along 2,232 miles (3,593 kilometers) of the Amazon and Orinoco rivers and their tributaries. (See video of dolphins spotted during the survey.)
The Bolivian river dolphin population may include as many as 25,000 individuals, making the mammal "very abundant," Ruiz-Garcia said.
And unlike the havoc wrought on its relatives by fishers on Brazilian rivers, Bolivia's newfound dolphin can roam safely through pristine freshwater channels.
Yet the mammal still remains vulnerable to environmental disruptions, experts say.
"They're very vulnerable predators," said Paul Van Damme, a researcher for Faunagua, a Bolivian organization that monitors dolphins. "So if fish are affected, they're the first to feel the effects."
For example, if a river fills with mercury, dolphins that eat contaminated fish consume the accumulated metal.
"The dolphins are a reflection of the entire aquatic system," Van Damme said.
(Related: "Last River Porpoises Dying in Polluted Yangtze" [April 23, 2008].)
The animal's greatest threat comes from a Brazilian dam that could raise the water level, alter the river flow, or divert the migration of fish, experts say.
A water-level rise could allow dolphins from both sides of the rapids to move back and forth again for the first time in over a hundred thousand years, Ruiz-Garcia said.
But such a reunion would soon turn tragic, he added.
"The Amazon river dolphin could compete against the Bolivian river dolphin for food, and perhaps bring about its extinction."
A new regional network of 18 scientists have created a conservation plan, which includes economic activities such as dolphin-watching ecotours.
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