Biology of the Galapagos Giant Tortoises
Biology of the Galapagos Giant Tortoises
The giant tortoise is probably the best known of all Galapagos animals and even gave the archipelago its name; 'Galapago' means tortoise in Spanish and may derive from the word for saddle, referring to the distinctive saddle-like shell of some of the tortoises. Galapagos giant tortoises can weigh up to 250 kg and live for more than 100 years. They are thought to belong to just one species, Geochelone elephant opus, with 14 different races or sub-species, three of which are believed to be extinct.
Persecution
In the 1600s, buccaneers started to use Galapagos as a base, restocking on water and repairing their boats before setting off to attack the Spanish colonies on the South American mainland. But the main attraction of the islands were the giant tortoises which were collected and stored live on board ship where they survived for many months, providing invaluable fresh meat. In the 1800s, whaling ships and then fur-sealers collected tortoises for food and many more were killed for their fine 'turtle oil' from the late 1800s until early this century. Early settlers then hunted them for their meat and cleared large areas of their habitat for agriculture. The settlers also introduced domestic animals, many of which went wild and had a disastrous effect on the tortoises.
No-one knows exactly how many giant tortoises there were originally but it has been estimated that more than 100,000 were hunted in total over the centuries. The result today is that three races of Galapagos giant tortoise are extinct while just one individual survives from a fourth. There are about 15,000 tortoises left altogether. As the hunters found it easier to collect the tortoises living round the coastal zones, the healthiest populations today tend to be those in the highlands. Persecution still continues on a much smaller scale; more than 120 tortoises have been killed by poachers since 1990.
Arrival
It is likely that all the present races of giant tortoise evolved in Galapagos from a common ancestor that arrived from the mainland, floating on the ocean currents. Although this seems an incredible journey it is known that Galapagos tortoises can float easily in sea water. Only a single pregnant female or one male and one female needed to arrive in this way, and then survive, for Galapagos to be colonised. It is likely that the...