River dolphins (also known as botos) are among the rarest, and most endangered, dolphins in the world. Three of the four known species are listed as “threatened” by the International Union for Conservation of Nature (IUCN). The discovery of a wholly new species—the first such find in a century—is thus exciting news for biologists and conservation officials.
Scientists led by Tomas Hrbek of the Universidade Federal do Amazonas in Manaus, Brazil, announced the existence of the proposed new species of river dolphin in PLOS ONE on January 22. Discovered in the Araguaia River Basin in central Brazil, the animals were isolated from other botos (Inia geoffrensis and Inia boliviensis) in the adjacent Amazon Basin to the west by a series of rapids and a small canal. As a result, the scientists suggest calling the new species the Araguaian boto, or Inia araguaiaensis.
The study scientists “make a strong case based on the data,” says Howard Rosenbaum, director of the Wildlife Conservation Society’s Ocean Giants program in New York. The discovery, he says, is “amazing because we’re starting to get insights into how these animals become distinct species.”
In the study, the Brazilian team concluded that the DNA of the Araguaian river dolphins is sufficiently different from that of other botos to warrant designation as a new species. The degree of difference suggests that the Araguaian boto most likely separated from other dolphin species more than two million years ago. Physical and genetic differences from other dolphins, they write, represent “strong evidence that individuals from the Araguaia River represent a distinct biological group.” (See pictures of river dolphins.)
The newly proposed species marks the first new discovery of a true river dolphin since 1918, when researchers identified Lipotes vexillifer, the Yangtze river dolphin or baiji, in China. The baiji was declared “functionally extinct” in 2006 after scientists failed to find even one individual.
Rosenbaum told National Geographic that the team in Brazil “did an admirable job in collecting a good amount of data on a species that is difficult to study in the wild.”
Rosenbaum, who specializes in genetic differentiation of dolphin and whale species, said the researchers had published “very robust data” showing genetic and physical differences between the Araguaian boto and other dolphins.
Rosenbaum said the scientists demonstrated some unique “diagnostic characters” in maternally inherited, or mitochondrial, DNA and other genes analyzed in their sample of river dolphins. Both lines of evidence, he says, “show that the Araguaian boto were separated from other boto for a long period of time.”
He added that the scientists described “some compelling size differences in cranial features, and potentially in their number of teeth.”
But Rosenbaum also saw reason for caution, because the scientists had only a few specimens in the study. Loath to kill living animals for study, the team relied on an animal that was found dead and a few samples that were already held in museums.
To bolster the case for naming a new species, “they will probably need to look at additional specimens,” said Rosenbaum.
The next step for naming a species will be to appeal to the Society for Marine Mammalogy, asking for a formal species designation. That scientific group will likely seek additional data, though the PLOS ONE paper is a solid first step, said Rosenbaum.
Threats to the River Dolphin
The scientists in Brazil observed about 120 of the Araguaian dolphins over 12 weeks. They estimate that as few as 600 of the animals could live in the entire river basin.
The scientists warn that all river dolphins face many threats, including dam construction, which can cut off the animals from others of their kind, limiting their reproduction opportunities. They are sometimes killed by local fishermen, who fear that they compete with them for fish, and they end up ensnared and killed by fishing gear.
“Since the 1960’s the Araguaia River basin has been experiencing significant anthropogenic pressure via agricultural and ranching activities, and the construction of hydroelectric dams, all of which have had negative effects on many biotic and abiotic aspects of the functioning of the Araguaia River ecosystem,” the study said.
Rosenbaum said more research needs to be done on precisely how these threats may impact the survival status of these animals.
He added, “As we address the tremendous threats these animals face, these amazing discoveries are so important because they will hopefully lead to better protecting them. It could start a domino effect for conservation.”
The researchers wrote that the Araguaian boto should be classified as “vulnerable” by IUCN. They added, “This discovery highlights the immensity of the deficit in our knowledge of Neotropical biodiversity, as well as vulnerability of biodiversity to anthropogenic actions in an increasingly threatened landscape.”