Silhouette National Park (6786)
Seychelles, Africa
Site overview
KBA status: confirmed
Global KBA criteria: A1e, B2
Year of last assessment: 2018
National site name: Parc National de Silhouette
Central coordinates: Latitude: -4.4870, Longitude: 55.2300
System: freshwater, marine, terrestrial
Elevation (m): 0 to 740
Area of KBA (km2): 18.51762
Protected area coverage (%): 98.91
KBA classification: Global
Legacy site: Yes
Site details
Site description: Located c.20 km north of Mahé, Silhouette is the third-largest and second-highest island of the granitic group. There is a great diversity of habitat on the island, from coastal reef-flats to mist-forest. There are two main plateaus, limited in size, each supporting coconut plantations and other man-made habitats, as well as relatively large wetlands and indigenous woodland. The rest of the island consists of densely vegetated steep slopes, impressive glacis and sheer cliffs which fall to the sea. Although exotic plants (e.g. Psidium cattleianum, Cinnamomum verum and Syzygium jambos) are present, they are less widespread than on the other large islands, and some areas still retain original forest-types from sea-level (Callophyllum inophyllum woodland) to high altitude (Pisonia sechellarum forest, unique to Silhouette). Only 11% of the 195 species of angiosperm recorded on Silhouette are introduced, while 34% are Seychelles endemics (including the trees Carissa sechellensis and Mimusops sechellarum), with 2% endemic to Silhouette (e.g. Achyrospermum sechellarum, Schefflera procubens and Amaracarpus pubescens). Silhouette has a human population of 135 (June 1999) with the majority living at La Passe; two families (six people) live at Grand Barbe and one couple at Anse Mondon. Human land-use covers only c.8% of the island, its steep gradients limiting major development. The main activities include the production of copra and cinnamon bark, fishing and tourism—there is a small hotel, served by helicopter from Mahé.
Rationale for qualifying as KBA: This site qualifies as a Key Biodiversity Area of international significance that meets the thresholds for at least one criterion described in the Global Standard for the Identification of KBAs. Alliance for Zero Extinction (2018): site confirmed as an AZE site during the AZE project (2015-2018). Taxonomy, nomenclature and Red List category follow the IUCN 2016 Red List.
Additional biodiversity: See Box and Table 2 for key species. The IBA contains 10–20 pairs of Falco araea. Silhouette is also of importance for Alectroenas pulcherrima (100–500 pairs), Hypsipetes crassirostris (500–2,700 pairs) and Nectarinia dussumieri (1,200–3,700 pairs). Other species include Streptopelia picturata picturata, possibly introduced, and Phaethon lepturus, which nests in trees. Three resident breeding waterbird species, Bubulcus ibis, Butorides striatus and Gallinula chloropus are common in wetlands of the plateaus. Non-bird biodiversity: Due to its wide range of habitats, Silhouette supports an exceptional diversity of indigenous fauna, which includes several species of insects (e.g an endemic stick insect Carausius scotti) and other invertebrates endemic to Silhouette or becoming rare on other islands. Amphibians comprise four species of frog and six caecilian species, while reptiles include Lamprophis geometricus, Lycognathophis seychellensis, Chamaeleo tigris, Mabuya sechellensis, four burrowing skinks (Pamelaescincus gardineri and Janetaescincus braueri) and four species of gecko, all endemic to Seychelles. The bat Coleura seychellensis silhouettae (CR) is present; the only roosting cave for the species currently known occurs on the island. The fruit bat Pteropus seychellensis is present in large numbers.
Habitats
Land use: agriculture | fisheries/aquaculture | not utilised | tourism/recreation
Threats
Summary of threats to biodiversity at KBA: The spread of exotic plants, particularly by the highly invasive Clidemia hirta, is a significant threat. A conservation project for the island exists (a joint NPTS / IDC / MET programme). NPTS has published a full species list for Silhouette. Captive-breeding projects for Seychelles giant tortoises Dipsochelys spp. and Seychelles terrapins Pelusios spp. are managed by NPTS at La Passe. This IBA is also a potential site for the translocation of Terpsiphone corvina, presently restricted to La Digue (SC006) (with a few on Marianne). A Marine National Park of 2,000 ha surrounds the IBA.
Additional information
References: Carlström (1996a, b), Cresswell et al. (1997), Gerlach (1993, 1997), Greig-Smith (1986), NPTS (1996), OUSE (1990), Rocamora et al. (1996).