An adult female Chelonoidis phantasticus, also known as the Fernandina Giant Tortoise, was spotted by a joint expedition of the Galapagos National Park and the US-based Galapagos Conservancy.

A spokesman said the female is more than 100 years old.

Investigators think there may be more members of the species on the island because of tracks and scat they found. The team took the tortoise to a breeding centre for giant tortoises on Santa Cruz Island.

The International Union for Conservation of Nature has the Fernandina Giant Tortoise listed as critically endangered and possibly extinct.

The only other living member of the species was found in 1906, the group said.

"They will need more than one, but females may store sperm for a long time," said Stuart Pimm, a professor of conservation ecology at Duke University.

Fernandina is the third largest Galapagos island and features the La Cumbre volcano, one of the most active in the world. The archipelago lies in the Pacific Ocean about 1000km off Ecuador's mainland.

In listing the Fernandina tortoise as possibly extinct, the conservation group said on its website that the species may have succumbed to "the frequent volcanic lava flows that nearly cover the island".

Australian Associated Press