Saving the Endangered Cuban Crocodile

The critically endangered Cuban crocodile (Crocodylus rhombifer) has many peculiar qualities, but perhaps the most intriguing one is its curiosity. For biologists conducting fieldwork in Zapata Swamp, Cuba's largest wetland and the only place in the world where the species is found, this is a notable trait. The crocs will investigate a campsite if nothing prevents them. Protective netting is deployed to keep them out, although not always successfully. "The animal comes inside the camp looking for a warm place to sleep beneath"—referring to human bodies in hammocks, says Etiam Pérez, a Cuban crocodile researcher and manager of the Zapata Swamp Captive Breeding Farm.

Pérez is speaking to Scientific American at the farm, beside an open-air pen that holds hundreds of young, brilliant, black-and-yellow Cuban crocodiles under the fierce Caribbean sun. The tropical facility claims more than 4,000 specimens of what Pérez calls "the most beautiful crocodile in the world." Like most Cuban operations it is government-owned, and was founded 57 years ago by Fidel Castro himself. A large black-and-white photograph of Castro hangs on a wall of the facility, complete with a lengthy quotation from the late autocrat praising Cuban crocodile conservation. The animal, Pérez says, holds a kind of political and symbolic weight in Cuba, especially in in the south-central Matanzas Province, where Zapata Swamp is located.

But the crocodile's vaunted status has not prevented its decline. Overhunting in the 19th and 20th centuries coupled with deforestation from increased development in modern times has reduced its population to historic lows. Scientists estimate only around 3,000 wild crocs are left, although even that number comes largely from guesswork. Now scientists are scratching their heads over another potential threat to these reptiles: interbreeding with American crocodiles (Crocodylus acutus).

The most widely distributed crocodilian species in the Americas, C. acutus, is native to Cuba (as well as the U.S.) and, unlike C. rhombifer, flourishing across the country. Scientists say the two species are morphologically, ecologically and behaviorally distinct from each other. Increased hybridization of the two poses an existential risk to the much less common Cuban species via a gradual erosion of its genetic identity. For conservation-minded scientists, this is worrying indeed. "The concern is that widespread hybridization might eliminate the unique Cuban crocodile through [such] genetic swamping," says George Amato, a conservation genomics biologist at the American Museum of Natural History.

Yoamel Milián-García, a biologist at the University of Havana, first published data on the hybridization epidemic in 2015. He analyzed scale clippings of 227 wild crocodiles and 137 farm-raised ones, finding that 49.1 percent of the wild specimens were hybrids and 16.1 percent of captive ones possessed mixed genes. "The degree of hybridization that we're seeing seems much higher than we would have predicted or imagined," Amato says. "Some people think it's the biggest threat" to these animals, he adds.

But nobody knows for sure. Hybridization could be a frightening species eraser. It could also be a normal historical process, says Amato, who has collaborated with Cuban biologists, including Milián-García and Pérez, on crocodile research there since the 1990s. Scientists simply do not have enough evolutionary or biological data yet to decide which interpretation is the right one.