NEWS: First successful invasive rat eradication in the Chagos Archipelago

British Indian Ocean Territory, 10 April 2017: Conservationists from the Chagos Conservation Trust (CCT) announced today the first successful invasive black rat eradication in the Chagos Archipelago.

“The success of eradicating invasive black rats from Ile Vache Marine is the initial step of a long-term strategy to eradicate these invasive alien predators from all of the affected islands within the British Indian Ocean Territory, in line with the British Indian Ocean Territory Administration’s conservation management framework “ said Pete Carr, CCT trustee and terrestrial biodiversity specialist.

With support from the British Indian Ocean Territory Administration, Carr and Dr Grant Harper, biodiversity restoration specialist, completed an expedition to the island of Vache Marine and found no sign of invasive black rats remaining and increased seabird numbers after a rat eradication operation was carried out during the 2014 Ile Vache Marine Restoration expedition to restore the island ecosystem.

“We know that globally invasive black rats have had a devastating impact on oceanic island ecosystems by suppressing populations of native animals and preventing regeneration of native plants” said Carr.

The small island of Vache Marine lies within a designated Strict Nature Reserve in the British Indian Ocean Territory Marine Reserve. In close vicinity are three designated and two proposed IUCN classified Important Bird Areas.

However, it was infested with rats like many islands in the Chagos Archipelago, and therefore inhospitable for endangered turtles and internationally important seabirds. Rats eat turtle and bird eggs, hatchlings, nestlings, and adult animals, completely suppressing population levels.

“Studies of the island have recorded that despite it being near to internationally important populations of breeding seabirds, only minuscule numbers of four species of seabird have ever been recorded as breeding on the island.” Carr continues.

“Successfully eradicating the black rats has, and will continue to, increase biodiversity on the island that provides a safe haven for seabirds to nest and contributes to a healthy ecosystem more widely.”

In 2014 CCT conducted an invasive black rat eradication operation as part of the Ile Vache Marine Restoration Project, funded by the Darwin Initiative. The project was delivered with over 30 days of dedicated vessel support from project partners, the British Indian Ocean Territory Administration. Ile Vache Marine can now officially be declared as rat free using the internationally recognised minimum period before declaration of rat free status of two years.

Throughout the Chagos Archipelago, introduced invasive black rats, accidentally introduced from ships in the 1700s, have been recorded as present on 26 islands, absent from 20 and their status uncertain on the remaining nine.


For more information contact:

Helen Pitman, Director, Chagos Conservation Trust, +44 7424 245661,

Notes to the editor:

1. Images and video available on request.

2. The Chagos Conservation Trust aims to ensure that the globally important natural environment of the Chagos Archipelago is well protected, conserved and understood, inspiring the better management and protection of our planet. 

3. The project was initiate and lead by Royal Marine Commando, Major Pete Carr rtd., a Chagos Conservation Trust (CCT) trustee. Technical lead was of Dr. Grant Harper, Biodiversity Restoration Specialists Ltd, who specialise in eradication of invasive alien species.

4. Project partners and stakeholders included: British Indian Ocean Territory Administration, Royal Society for the Protection of Birds, Royal Botanic Gardens Kew, British Forces stationed on Diego Garcia, British Indian Ocean Territory.

5. The 2014 project was funded by the Darwin Initiative, a Defra scheme to fund environmental projects in UK Overseas Territories.

6. The aim of the 2014 project was to: to restore the ecosystems of Ile Vache Marine by eradicating the invasive black rat (Rattus rattus), which will improve the breeding conditions for Critically Endangered hawksbill and Endangered green sea-turtles; allow for the re-colonisation of seabirds from the surrounding six Important Bird Areas; and promote native plant regeneration. Island ecological restoration has been successfully conducted elsewhere and is seen as the only method available to increase biodiversity and biomass of original species. In order to eradicate the rats this project will also manage other non-indigenous species, particularly coconut palms, preventing them from further constraining the native vegetation.

7. The main outputs from the 2014 expedition were:

  • The necessary baseline data was gathered by ornithological and botanical scientists to add to historical data on invertebrates and reptiles.
  • Crab abundance was gathered pre-operation by Pete Carr and a Chagossian Connect Chagos graduate
  • Habitat management including planting of native trees to replace the unmanaged coconuts was undertaken by Pete Car and Connect Chagos graduate and CCT trustees Claudia Naraina
  • Working closely with British Forces stationed on Diego Garcia over the period of two weekends, volunteer military personnel and Mauritian and Seychellois workers undertook the habitat management necessary for the hand-dispersal operation
  • A reconnaissance visit was lead by former Royal Marine officer, Jon Slayer, with Dr. Harper in January 2014

8. Evidence of no rats on the island came from:

  • increased seabird numbers, present, breeding and roosting
  • increased invertebrate numbers
  • increased seed germination
  • no paw prints in wet mud and sand and no rats visiting a series of bait stations during observation periods
  • no rats visiting the camp site (they always come routing around camps),
  • no rats caught in snap traps
  • no evidence of rats chewing on gnaw sticks
  • no rats observed on searches by flash light throughout the night (always seen at night by torch)
  • no rats seen anywhere around the island (prior to baiting rats have been seen within 10 minutes of arriving on the island

9. This suite of indicators, not just one, all point to the project as being declared as successful.

10. The Chagos Archipelago is located in the Indian Ocean, and forms the British Indian Ocean Territory. It is home to an astonishing diversity of life, and acts as a refuge for many threatened species. By conserving and restoring this precious environment, we can contribute to important marine conservation and learn much about the natural ecosystems of our world.

11. The Territory is one of 14 British Overseas Territories and administered from London by the British Indian Ocean Territory Administration. Access is restricted and a permit is required in advance of travel from the Administration.

12. Black rats were present in numbers enough to ruin crops by 1786[1] and were most likely accidentally introduced during the first attempts at permanent settlement by the French and British in the late 1700s, though Portuguese mariners had been prospecting the area two centuries prior and may have been the perpetrators.

13. Although eradications of rats from islands has been successfully carried out since their tentative beginnings in the 1980s, the vast majority of these have been in temperate zones where the technique relies on targeting rats during winter when they are under stress as food supplies are restricted and breeding has ceased. On tropical islands food is freely available and breeding can occur year round. Moreover, non-target species like land crabs are in high numbers and can quickly remove poison bait. For these reasons the failure rate of rat eradications on tropical islands has been higher than on islands in cooler latitudes.[2]

14. The internationally recognised minimum period before declaration of rat free status can occur is two years.

15. Important Bird and Biodiversity Areas are identified using internationally agreed criteria applied locally by BirdLife Partners and experts.

[1] Carr and Harper, (2016), The Distribution of Ship Rat Rattus rattus in the Chagos Archipelago, Chagos News Issue 49.

[2] Carr and Harper, (2016), The Distribution of Ship Rat Rattus rattus in the Chagos Archipelago, Chagos News Issue 49.