The Stand-In Tortoises
Mauritius lost its giant tortoises around 1800, and with them the only animal on the island large enough to swallow an ebony fruit and carry the seed anywhere at all. In 2000 a Mauritian conservation charity did the thing nature reserves exist to prevent — released a foreign species inside one, on purpose — and the experiment has since become a recognised category of restoration.
The tortoise on the path at Île aux Aigrettes has right of way and knows it. It is working on a fallen ebony fruit, taking it in whole, and it will spend the rest of the morning moving perhaps forty metres under the replanted canopy. Visitors come round it on the seaward side. The guide waits. Nothing about the scene reads as an intervention, which is the point of it.
The animal is an Aldabra giant tortoise, and its home atoll is about 1,700 kilometres away in the Seychelles. It did not arrive by accident, and it did not arrive as an ornament. It was carried onto a Mauritian nature reserve under permit in 2000 in order to perform a specific piece of work that a Mauritian animal did until roughly 1800 and that nothing has done since. This island is where that idea was first tested properly, measured, and found to work.
The gap the tortoises left
Mauritius, Rodrigues and Réunion each had their own giant tortoises — five species in the genus Cylindraspis, found nowhere else on earth. They were slow, unafraid, and stayed alive for months in a ship's hold without food or water, which made them the perfect provision for a sailing vessel and killed every one of them. The Huguenot François Leguat, marooned on Rodrigues from 1691, described herds he put at two or three thousand animals. Within roughly a century of his account, across all three islands, the genus was gone. What went with it was not only an animal. It was the only mouth in the forest big enough to swallow the fruit of the local ebony, Diospyros egrettarum, and the only set of legs heavy enough to carry the seed away from the parent tree and grind down the seedlings of everything else. The ebony survived on Île aux Aigrettes. Its recruitment did not: seed fell where it fell, germinated in its own shade, and went nowhere.
A permit to introduce a foreign animal
Île aux Aigrettes is twenty-six hectares of coral limestone in the bay off Pointe Jérôme, a declared nature reserve since 1965 and leased to the Mauritian Wildlife Foundation, a Mauritian charity founded in 1984, from 1985. By the late 1990s the Foundation had spent more than a decade on it, latterly alongside the government's National Parks and Conservation Service, which had only existed since 1994 — rats removed, invasive plants pulled out by hand, natives propagated and put back. The remaining problem was not botanical but mechanical: the forest had no large herbivore in it, and no amount of planting supplies one. Deliberately releasing a non-native animal into a protected area is precisely what conservation law is built to prevent, and the case for doing it here rested entirely on containment. A small island with sea on every side. An animal that cannot swim, moves at a speed you can walk beside, is trivial to count, and can be lifted into a boat and taken off again if the answer turns out to be wrong.
The tortoise is not there to be a tortoise. It is there to be a mouth, a gut and a pair of feet the island stopped having around 1800 — and if it proves to be the wrong answer it can be picked up and carried away, which is true of almost no introduction ever made.
What was actually measured
The release was designed as an experiment rather than a gesture, which is why it is quoted everywhere and most restoration work is not. Animals were tracked. Droppings were collected and grown on. Plots with tortoises were compared against plots without them. Ebony seed came through the gut intact and germinated, and ebony seedlings began appearing away from parent trees for the first time in about two hundred years. The tortoises also grazed hard on the seedlings of introduced weeds, doing for nothing the work that had been costing the Foundation a season of hand-weeding. Results were published in the restoration literature from around 2010 and are the reason anybody outside Mauritius knows the island's name. The honest limits were published with them. An Aldabra tortoise is not a Cylindraspis; it eats some things its predecessor probably did not, and the population on the island is capped, fenced out of sensitive areas, and managed rather than left to find its own level. The method is a controlled substitution, not a resurrection, and its defenders have never claimed otherwise.
Round Island
Twenty-two kilometres north of Mauritius there is a volcanic cone with no landing beach, no fresh water and no public access. Round Island is the last place on earth holding the keel-scaled boa, the only surviving member of a snake family that existed nowhere but here; its relative, the burrowing boa, was last seen in 1975. Several of its palms grow wild nowhere else, and one of them is down to a handful of individuals. Goats and rabbits put ashore in the nineteenth century ate it back to rock and took most of the topsoil with them into the sea. The goats were gone by 1979. The rabbits were eradicated in 1986, in one of the earliest operations of that kind attempted anywhere, and the vegetation began to return — but again with nothing on the island large enough to move a seed. Aldabra tortoises were released there in 2007, for the same reason and on the same reasoning, onto ground that no visitor will ever walk.
What Mauritius exports now
This is a country that lost a larger share of its native plants and animals than almost anywhere on the planet, and it has become one of the places other countries come to for technique. The Mauritius kestrel was down to four known wild birds in 1974 and now numbers in the hundreds. The echo parakeet passed through the 1980s with fewer than twenty individuals left. The pink pigeon was at about ten birds in 1990 and is now a working population that visitors meet on a footpath. The legal scaffolding came later than the work — the Wildlife and National Parks Act in 1993, Black River Gorges declared a national park in 1994 — and the hand-weeded plots inside that park are the same argument as the tortoises, made with secateurs instead. In 2013 the IUCN issued its Guidelines for Reintroductions and Other Conservation Translocations, and ecological replacement, the deliberate use of a substitute for an extinct species, was written in as a recognised category with the Mauritian work behind it. None of that brings back a Cylindraspis. What has come back is the job it did, and on an island where the alternative was watching an ebony forest quietly stop reproducing, that turned out to be the part worth saving.