Although Silhouette is the third largest island in Seychelles and Mont Dauban the second highest mountain (740m), the island's steep slopes have prevented significant development and restricted the population to 147 people at the present time. As a result, human impact has been less significant than on other islands and much of the original nature of the Seychelles islands is preserved on Silhouette.
The height of the mountains and the limited amount of development means that the island has an exceptional range of unique animals and plants. It is regarded by conservationists as one of the most important biodiversity hotspots in the Indian Ocean. Silhouette is recognised as a priority site for conservation by the Alliance for Zero Extinction.
Most of Silhouette is formed of 63 million years old granites. As with the other granitic islands in Seychelles these rocks are remains of the ancient southern super-continent Gondwana. This geological history means that the islands are the sunken remnants of the mountains of a continent once joined to India and Madagascar. Clinging to these mountain-tops are the remains of the flora and fauna that coexisted with the dinosaurs. At the time when the dinosaurs became extinct, part of Silhouette was covered by a volcano, traces of which can still be found.
Silhouette was the first island of the group to be seen when the islands were discovered in 1609 but was not settled until the early 19th century.
From 1860 attempts were made to develop parts of the island for agriculture or forestry. A wide range of plants was introduced for crops of timber, fruit, spices and oils. These are all abandoned now but the plants can still be found growing in the most unlikely places. In the 1940s a small grove of Coco-de-Mer trees (Lodoicea maldivica) was planted high in the mountains. This thriving population of this rare palm provided an occupation for part of the 1000 strong labour force on the island, some of whom had to climb up to the trees to water them daily. The dramatic legacy of the island's history; a cast-iron neo-classical mausoleum, is the most remarkable piece of eccentricity in all Seychelles.
Since 1983 the island has been managed by the Islands Development Company (IDC).
Conservation and the Silhouette Conservation Project
In 1987 the waters around Silhouette were declared a Marine National Park and the rest of the island was protected as the Silhouette National Park in 2010. In 1994 the IDC invited The Nature Protection Trust of Seychelles (NPTS) to assist with conservation management of the island. In 1997 the NPTS established its Silhouette Conservation Project on the island. This project aimed to protect the forest environments of Silhouette and to restore them to a near-natural state. A large part of the conservation work involved research into the diversity and ecology of the forest animals and plants. Another important aspect was the control of invasive species. This work came to an end in 2011 when the Seychelles government organsiation which owns Silhouette evicted conservationists from the island.
The NPTS Seychelles Giant Tortoise Conservation Project used to be based on Silhouette.
Plants and animals of Silhouette
The NPTS conducted research on Silhouette's biodiversity from the early 1990s until 2011. This led to the compilation of a full species list, covering nearly 2,000 species and the research was published in the NPTS journal Phelsuma.
The majority of plant and animal species are small and inconspicuous. The most obvious animals are the large fruit bats (Pteropus seychellensis), abundant bird life, day geckos (Phelsuma spp.) and skinks (Mabuya sechellensis, Pamelascincus gardineri and Janetascincus braueri). There are many inconspicuous or secretive animals, most dramatic of which is the Seychelles chameleon (Archaius tigris). Both hawksbill turtles (Eretmochelys imbricata) and green turtles (Chelonia mydas) nest on the island. The island is of great importance as it supports the last known major roosts of the Seychelles sheath-tailed bat (Coleura seychellensis).