JUANA SUMMERS, HOST:
And now a surprising kind of rock climber that uses its fins to cover some impressive vertical ground. Here's science reporter, Ari Daniel.
ARI DANIEL, BYLINE: Pacifique Kiwele Mutambala is a PhD student at the Universite de Lubumbashi in the Democratic Republic of Congo. He says that 17 years ago, a researcher from his university traveled to a waterfall in the south of the country where he saw something remarkable.
PACIFIQUE KIWELE MUTAMBALA: Some fishes can climb up the waterfalls.
DANIEL: That's right. Tiny fish called shellears, each one the size of a fat French fry, climbing up the 50-foot rock face behind the waterfall. This behavior has been documented in fish in other parts of the world, but Mutambala says never in Africa. That researcher 17 years ago filmed the phenomenon but ended up losing the footage. So there's no hard evidence. And Mutambala, as a master student, was determined to go get some.
MUTAMBALA: This is important for the biodiversity and the conservation.
DANIEL: Because if the shellears are vertically migrating, then cutting off the water supply to this waterfall to fill a dam or for irrigation, which does happen, could harm the fish. So for a few years running, during the rainy season, Mutambala visited the falls, which you can hear in this video that he took, in search of upwardly mobile fish.
(SOUNDBITE OF WATERFALLS)
MUTAMBALA: I tried to go close to the falls and observe very clearly what fishes can do.
DANIEL: And sure enough, he saw thousands of them shimmying up the vertical rock surface, seemingly defying gravity.
MUTAMBALA: Ah. The first time, I was very excited. Yes. Yes, very excited.
STEVEN COOKE: Yeah. It really reinforced to me just how cool fish are, right?
DANIEL: Steven Cooke is a fish ecologist at Carleton University in Ottawa, who wasn't involved in the research.
COOKE: The scale is really impressive. That would be like a salmon trying to make it over Niagara Falls or climb the CN Tower.
DANIEL: He says the shellear migration may seem to pale in comparison to something like that of the wildebeest, but it's just as important.
COOKE: Migratory fish are several times more at risk of endangerment or extinction than fish that don't migrate.
DANIEL: Which means, he says, it's necessary to protect the habitat across the entire range of the species, waterfalls and all. Now, one of the big questions the researchers had was how the shellears climb. So in the lab, they reviewed the fish's movements in the video footage and ran CT scans of the fish to examine their anatomy. They saw that they support themselves with their rear fins, and on their front fins, they have an array of single-celled hooks that function kind of like Velcro, which they use to grip the rock. And...
EMMANUEL VREVEN: You see also the lateral undulations of the fish - very fast. It's as if they are swimming vertically.
DANIEL: Wriggling their way gradually upward, says Emmanuel Vreven. He's an ichthyologist at the Royal Museum for Central Africa in Belgium and helped supervise the research.
VREVEN: Most of the time is, in fact, resting.
DANIEL: Sometimes they cling to an overhang, upside down. Some fish fall down and have to begin again. The entire ascent takes close to 10 hours.
VREVEN: Yeah. So it's an enormous effort.
DANIEL: As for why they do it, maybe there's better food up there or less predation. Either way, the researchers say it's the first time the behavior's been formally documented on the African continent. The results appear in the journal Scientific Reports. For NPR News, I'm Ari Daniel.
(SOUNDBITE OF TLC SONG, "WATERFALLS") Transcript provided by NPR, Copyright NPR.
NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.
