British Indian Ocean Territory

Invasive species and biosecurity

A total of 262 non-native species (marine and terrestrial) was recorded for BIOT by the RSPB Stocktake (Churchyard et al 2014).

Taxon Total species Non-native species
Invertebrates 1,302 6
Vertebrates 1,002 21
Plants 534 235

Problems with invasive non-native species

Over half of the islands in the archipelago have been degraded because of invasive species. Most of the islands in the group are rarely visited but there are black rats (Rattus rattus) on at least 30 of the islands and feral cats and donkeys are present on Diego Garcia.

House geckoes (the common house gecko Hemidactylus frenatus and Mourning gecko Lepidodactylus lugubrus) have been present on Diego Garcia for many years, probably arriving in the first ships. The agamid lizard Calotes versicolor was first seen in 2001 and is spreading over the island.

Indications are that seabird numbers are significantly reduced on rat infested islands. Marine Toads (Rhinella marina) are also present on Diego Garcia and are regarded as an introduced species of conservation concern. Coconut Palms have dominated or replaced native vegetation on a number of islands.

For stories and information on the introduced fauna of Diego Garcia see

Introduced agamid lizard Calotes versicolor playing dead.

Priority invasive non-native species and actions

There is an ongoing programme of cat eradication on Diego Garcia.

A rat eradication project on Eagle Islands in 2006 failed. Black rats were successfully eradicated from Ile Vache Marine in 2014, with the island declared rat-free in 2017.


A biosecurity gap analysis was done in 2017 and details can be found here. BIOT does not have dedicated biosecurity officers. There is a customs team who inspect luggage and personnel for contraband items (drugs etc), who receive biosecurity training on checking for plant and animal material in both containers and in personal luggage. The customs team look at all containers coming onto the island for infestations. If they see any evidence of this, they seal the containers and get pest control in to treat the affected container. Imported materials (large granite rocks) for coastal defence are inspected for the presence of soils etc. These are stored on a concreted area for a period of c.28 days before being utilized. Public awareness is good, with regular monthly training covering the introduction of invasive species, pests, and twice a year training on Brown Tree Snake and other invasive species awareness. An on island review of procedures during all stages of container arrival and departure is being carried out during the beginning of 2020 to address gaps in knowledge.

A pathway analysis was done in 2018 and details can be found here. Pathways of introduction are relatively few. There is a military airport and harbour on the main island, Diego Garcia. There are no commercial flights and permits are only issued to yachts in safe passage through the archipelago. Between 2007 and 2017 an annual average of 50 yachts were issued licenses to visit BIOT, varying from 16 to 105.

Cargo arrives by both ship and plane. Within the region, cargo is flown in from Bahrain and Singapore and by cargo ship from Singapore and Guam. Military passenger planes arrive from Bahrain and Singapore, each approximately two to three times a week. Other military vessels (including submarines) can come from anywhere and berth in Diego Garcia, while other military flights can come from Okinawa (Japan), Australia and other points of origin. These are generally on short stop-overs. A patrol vessel travels between Diego Garcia and the outer islands, which may take shelter in the lagoon of outer islands. Smaller rib boats are used for landing and passengers swim ashore. Military ships also move within the archipelago, berthing alongside the wharf in Diego Garcia and anchored off shore in the outer islands.

Horizon scanning was carried out in 2019, identifying a total of 27 new invasive species of concern which have the potential to arrive within the next 5 – 10 years; details can be found here.

Thin strip of image show tree trunk and bark