How Did the Tortoise Cross the Strait?

For as long as people can remember, the spur-thighed tortoise, Testudo graeca graeca has been found on both sides of the Strait of Gibraltar: in North Africa, southern Spain, and a few Mediterranean islands.

An estimated 64.5 percent of children in southern Spain keep or have kept a spur-thighed tortoise in captivity—mostly those that they’ve found in their own backyards. Tortoise-keeping, in other words, is as Spanish as cured ham. Spur-thighed tortoises, however, are not.

As it turns out, no spur-thighed tortoises fossils have ever been found in Spain. Moreover, a paper published last year in Conservation Genetics posits that the tens of thousands of animals now in captivity or roaming the wilds there have their roots in Morocco and Algeria, where the wild populations are much more diverse. Some tortoises may have once lumbered across an ancient land-bridge, but today the endangered critters are ferried across the strait every year with the help of tourists.

On a recent afternoon in the traditional market, or souk, in Marrakech, Morocco, a vendor offered me a string of dozen dried chameleons for a couple of dollars “for my garden” as he put it. Another had a tattered leopard skin on the offing for $60, although I’m sure it could be had for far less. And in a nearby basket, six or seven spur-thighed tortoises clambered atop each other: a pocket-sized souvenir from the timeless wildlife trade.

In Smithsonian’s December issue, Charles Bergman wrote about animal trafficking in the Amazon, but the phenomenon is all the more shocking here in Morocco where such items are sold directly to tourists who probably should know better. Last August, customs officials in France seized 20 tortoises imported from Morocco without the proper paperwork, and in December officials in the United Kingdom nabbed four. In that recent genetic study, one of the tortoises reported to be wild-caught from Spain had the genetic fingerprint indicating it was an introduction from west Morocco.

All this raises questions about how to conserve a “native” species in a region where people may have been moving animals around for tens or even hundreds of thousands of years. The authors of the Conservation Genetics paper suggest that endangered tortoise populations in North Africa and Spain be managed independently because they have each adapted to their local environments. But one could also argue that a little African blood in Spain could give those tortoises the genetic variability they need to survive in the long-term.

Brendan Borrell will be guest blogging this month. He lives in New York and writes about science and the environment; for Smithsonian magazine and Smithsonian.com, he has covered the ecology of chili peppers, diamonds in Arkansas and the world's most dangerous bird.