Giant tortoises are roaming the Galápagos island of Floreana for the first time in more than 180 years, in what conservationists have called a "hugely significant milestone".

The release of 158 captive-bred juvenile tortoises onto the island is part of the Floreana Ecological Restoration Project led by the Galápagos National Park Directorate.

The reintroduction follows a "back-breeding" programme launched in 2017 after scientists discovered tortoises carrying ancestry of the Floreana giant tortoise on nearby Isabela island.

Floreana's native species, Chelonoidis niger niger, was driven to extinction in the 1840s by sailors who took thousands from the island for sustenance during long voyages.

"The restoration of Floreana has reached a hugely significant milestone, with 158 captive-bred giant tortoises released into the wild this week," the Galápagos Conservation Trust (GCT) said in a statement on Friday.

"This long-anticipated moment gives hope, not just for the future of Floreana, but for the future restoration of islands around the world," it added.

Dr Jen Jones, GCT chief executive, described the moment as "truly spine-tingling," adding that it had validated two decades of collaboration between scientists, charities and the local community.

The conservation project became possible after scientists discovered tortoises carrying Floreana ancestry on Wolf Volcano on Isabela island in 2008.

Researchers selected 23 hybrid tortoises with the closest genetic links to the extinct subspecies and began breeding them in captivity on Santa Cruz island.

By 2025, more than 600 hatchlings had been produced, with several hundred now large enough to survive in the wild.

The GCT described the giant tortoises as "ecosystem engineers" and said they played an "outsized role in restoring degraded ecosystems" because of the way their activity shapes landscapes.