Introduction to Ile aux Aigrettes, Mauritius, of the Aldabra giant tortoise as an ecological replacement for the extinct Mauritian tortoise

Summary

All five native Mascarene giant tortoise species, including the Mauritian tortoise (Cylindraspis inepta), went extinct by the mid-1800s, eliminating the grazing, trampling and seed-dispersal functions they once performed for native plant communities. The Mauritian Wildlife Foundation introduced the non-native but taxonomically close Aldabra giant tortoise (Aldabrachelys gigantea) to Ile aux Aigrettes, a 26-hectare predator-free islet with restored native forest, as an ecological replacement to test whether these functions could be restored. Four tortoises were first kept in a small enclosure in the 1990s for feeding-preference studies, then moved into a 1-hectare fenced area in 2002 where the herd grew to 20 animals and began breeding naturally within the first year; since late 2004 the tortoises have roamed the island freely. By 2017 the free-roaming population stood at 25 breeding adults producing 60-100 hatchlings annually, despite some geriatric health problems, two euthanized animals, two removed for poor health and two lost or stolen. Poaching of hatchlings for the pet trade led the project to head-start young tortoises in captivity before translocating them to Round Island, establishing a second wild population, while ongoing research tracks vegetation impact, seed dispersal and, through metabarcoding of droppings, the full range of plants the tortoises consume. The project rates itself successful, crediting careful selection of a taxonomically close, keystone-species replacement, rigorous long-term monitoring, and close collaboration between the Mauritian Wildlife Foundation, universities and the private sector; its results are informing a similar proposed introduction in Rodrigues.