Hiding in plain sight, researchers have discovered a new species of humpback dolphin living off the northern coast of Australia.
The discovery came when scientists with the Wildlife Conservation Society (WCS) tried to settle a decades-old argument among marine mammal researchers.
"For many years, there's been this debate about the number of species of humpback dolphins," said Howard Rosenbaum, director of the WCS ocean giants program. Scientists have proposed everything from two to four species within the group’s genus Sousa.
But there was never enough good evidence supporting claims of more than two species, Rosenbaum said. So about ten years ago, the community decided that until they had more information, they'd recognize only two species—the Atlantic humpback dolphin and the Indo-Pacific humpback dolphin.
Rosenbaum and colleagues decided to revisit this old argument, and started collecting physical and genetic samples from humpback dolphin populations throughout their range. This included samples from West Africa, the Indian Ocean, the Pacific Ocean, and off the coast of Australia.
"From a management standpoint, the marine mammal community has specified that they need at least two different forms of evidence to justify different species [designations]," said Rosenbaum.
So he and his colleagues tried to collect as comprehensive a data set as possible to get the best chance of putting this argument to rest. Usually, genetic analyses into the question of new species consider only DNA from an organism's mitochondria—the cell's battery pack.
This is because mitochondrial DNA is inherited only through the mother and is easier to work with than DNA from a cell's nucleus, said Martin Mendez, assistant director for the Latin American and Caribbean program at WCS.
But Mendez and colleagues looked at DNA from both parts of the cell. That, combined with physical characteristics including the length of the dolphins' beaks and the number and position of their teeth, suggested there were four species of humpback dolphin. Not two.
Three of those species were ones researchers had previously proposed. They encompass a species off of West Africa (S. teuszii), one in the central and west Indian Ocean (S. plumbea), and one in the eastern Indian and west Pacific Oceans (S. chinensis).
The fourth species, an as-yet unnamed group off the north coast of Australia, was a pleasant surprise, said Rosenbaum. (Related: "From Darth Vader to Jelly Doughnuts, Weird Species Names Abound.")
In some ways, this species is new to science, said Mendez. But in other ways, it isn't because researchers have known about this group down in Australia for a while. They just didn't realize it was a different species.
It's rare to find a new species of mammal, said Mendez. "[But] it's also not crazy to find new species when you're using the kind of [genetic] information we're using.
"One of the reasons we're finding new species is because we're finding new tools," he explained. "Genetics opens a new window into these kinds of questions."
Mendez is hopeful that this discovery—reported this week in the journal Molecular Ecology—will help in the management of this IUCN Red List group. The Atlantic humpback dolphin is considered vulnerable, and the Indo-Pacific group is considered near threatened.
The legal framework used to protect vulnerable species is based on species designations, he explained. "We're proposing that Australia has its own humpback [dolphin] species, which has implications for conservation strategies."
"Countless dolphins die every year as bycatch in fisheries," said Rosenbaum. The humpback dolphin is subject to particularly high rates of bycatch, and in some places is hunted directly.
"By describing these different species, we hope that this sets the stage not only for the appropriate conservation protections to be put in place by different countries, [but that] it also helps reduce threats like bycatch."
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