The answer, it turns out, is simple. They’ve been hiding. When Charles Darwin visited the Galapagos Island of Floreana in 1835, he found no sign of its native tortoise and assumed that whalers, pirates and human settlers had done them over. Since about 1850, there has never been a tortoise on the Island (bar one or two introduced animals kept as pets by the locals). It makes sense, therefore, that the IUCN should classify the Floreana tortoise Chelonoidis elephantopus (sometimes also Chelonoidis nigra nigra) as extinct.
|A direct descendant of Chelonoidis elephantopus, alive and well on Isabela. Courtesy of Yale University|
But the Yale geneticists now have good evidence that some purebred Floreana tortoises may still be alive on a different Island in the archipelago. For more than a decade, the researchers have been absorbed by the bizarre mixture of genes found in the tortoises on Wolf Volcano at the northern tip of Isabela, the largest Island in the volcanic chain. They began by studying mitochondrial sequences, which suggested that tortoises from the distant islands of San Cristobal and Espanola has somehow reached Wolf. Their guess was – and still is – that whalers and pirates were responsible. “Tortoises were occasionally stashed on various islands for safe-keeping and even tossed overboard in large numbers in nearshore areas to lighten cargo during flight or battle,” they wrote in 2002.
When I wrote my Galapagos book Lonesome George, I was fascinated by this possibility and looked hard for some first-hand evidence of such an introduction near Wolf volcano. I found it in the diaries of Captain David Porter, skipper of the infamous US frigate Essex that ruled Galapagos waters during the war of 1812.
|David Porter, captain of the USS Essex|
|USS Essex in full sail|
On 29 April 1813, with no wind to give chase, Porter sent several little boats out filled with armed men to capture the British ships Georgiana and Policy. What follows is lifted from my book:
Those on board the Georgiana and Policy were taken by surprise. If the rowing boats reached them, they would have to fight at close quarters and casualties could be heavy. With no wind, there was no escape. Their only hope was to blast the small boats out of the water. They were woefully unprepared, particularly as they had just stocked up on tortoises, which were getting in the way. ‘In clearing their decks for action, they [threw] overboard several hundred Galápagos terrapins’, wrote 12-year-old Essex midshipman David Farragut in his diary. Farragut was in one of the rowing boats closing on the Georgiana:
The appearance of these [land] turtles in the water was very singular; they floated as light as corks, stretching their long necks as high as possible, for fear of drowning. They were the first we had ever seen, and excited much curiosity as we pushed them aside.
As Farragut and his fellow men picked their way through a sea of giant tortoises, the cannon fire began. Back on the Essex at a safe distance, Porter looked on: ‘At two o’clock, the boats were about a mile from the vessels ... when they hoisted English colours, and fired several guns. The boats now formed in one division, and pulled for the largest ship, which, as they approached, kept her guns trained on them.’ None of the canons hit their mark. The boats ‘rowed up beneath the muzzles of the guns and took their stations for attacking the first ship’, Porter explained in a letter back to his superiors in Washington. The British struck their flag and stood down without a shot being fired. They then left a crew on board and took their stations for attacking the other vessel, the Policy; her flag was also struck.
‘Thus were two fine British ships ... surrendered, without the slightest resistance, to seven small open boats, with fifty men, armed only with muskets, pistols, boarding-axes and cutlasses!’ Porter boasted ‘that Britons have either learned to respect the courage of the Americans, or they are not so courageous themselves as they would wish us believe’.
As dawn broke a couple of days later, the Essex with her three prizes in tow was surrounded by about 50 live giant tortoises. They were rounded up and brought on board. According to Porter’s journal, ‘they had been lying in the same place where they had been thrown over, incapable of any exertion in that element, except that of stretching out their long necks’. He and his crew ate these tortoises in the coming months, but presumably some of those jettisoned by the embattled British ships were never recaptured. One or two, perhaps, made it to the nearest shore. We know from Porter’s letter to Washington that this would have been the northwest coast of Isabela, from which a beached tortoise could have made it to either Puerto Blanco or Puerto Bravo.
|Here's David Farragut, presumably a little later in his career|
It would be great to know where the Georgiana and Policy had been before they were captured, as this would give us the identity of the tortoise species they had on board. I never succeeded in locating their logbooks, which would have given this information but wouldn’t it be rather neat if they’d just come from Floreana carrying some of its last tortoises to a new life on Isabela? If anyone knows of the whereabouts of these logbooks – presumably captured by Porter and taken to the US along with the British vessels themselves – please, please let me know.
Anyway, back to the study on tortoises with which I began this post. With technological advances over the last decade and the tumbling cost of sequencing, so the Yale researchers have been able to mine the Wolf tortoise DNA in ever-greater depths. In 2007, they found evidence that this volcano might be harbouring close relatives of Lonesome George – the famed solitary survivor of the Pinta tortoise species. Using ancient DNA from museum-based specimens, they were also able to characterize the genetic signature of the Floreana tortoise and show that some Wolf tortoises have clear signs of this ancestry.
This latest study, published this week in Current Biology, takes this a step further by sampling a massive 1669 giant tortoises from Wolf, estimated to 20% of the volcano’s population. In amongst these, they have found 84 tortoises that have to have had a purebred C. elephantopus as one of their parents. They estimate that at least 38 founders would have been needed to leave the genetic footprint observed. Although most of these will have died out, it’s known that giant tortoises can live for more than 150 years and there’s a good chance there are still purebred Floreana tortoises out there.
The trouble is finding them. In 2008, it took a combined team of geneticists and rangers from the Galapagos National Park – some 40 people! – around 11 days of hard graft to sample 1/5th of the Wolf population. If purebred Floreana tortoises are still on the volcano, they are likely to be in very low numbers, says Ryan Garrick, Yale postdoc, now assistant professor at the University of Mississippi and lead author on the paper. “We would have to be very lucky to directly sample one of them.” Even if they can’t, however, their hybrid descendants could still be useful. "Hybrids may provide opportunities to resuscitate an 'extinct' species through intensive targeted breeding efforts,” he says.
It would certainly be of interest to those conservationists involved in Project Floreana, a huge initiative to put the island on a new, sustainable course, eradicating invasive species like cats and rats, restoring lost natives like the critically endangered Floreana mockingbird and bringing the island’s human residents on side. Wouldn't it be great to be able to include bona fide Floreana tortoises rather than just some stand-in surrogate?
The snag is that locating hybrid tortoises on Isabela’s Wolf volcano, transporting them to captivity and finding money to fund a back-crossing breeding programme over several decades would be seriously expensive. With Galapagos facing a multitude of pressures, not least from indirect impact that 30,000 residents and 170,000 annual visitors have on such a fragile place, is restoring the Floreana tortoise a priority? Or is it a luxury the cash-strapped conservation movement can ill afford?
This post is based on an article published on the Nature News blog on 9 January 2012.