 Tortoise numbers declined from over 250 @,@ 000 in the 16th century to a low of around 3 @,@ 000 in the 1970s . This decline was caused by overexploitation of the species for meat and oil , habitat clearance for agriculture , and introduction of non @-@ native animals to the islands , such as rats , goats , and pigs . The extinction of most giant tortoise lineages is thought to have also been caused by predation by humans or human ancestors , as the tortoises themselves have no natural predators . Tortoise populations on at least three islands have become extinct in historical time due to human activities . Specimens of these extinct taxa exist in several museums and also are being subjected to DNA analysis . Ten subspecies of the original 15 survive in the wild ; an 11th subspecies ( C. n. abingdonii ) had only a single known living individual , kept in captivity and nicknamed Lonesome George until his death in June 2012 . Conservation efforts , beginning in the 20th century , have resulted in thousands of captive @-@ bred juveniles being released onto their ancestral home islands , and the total number of the species is estimated to have exceeded 19 @,@ 000 at the start of the 21st century . Despite this rebound , the species as a whole is classified as " vulnerable " by the International Union for Conservation of Nature . 
