Chagos Archipelago

Chagos coral reef

The British Indian Ocean Territory (BIOT) is one of the UK’s 14 Overseas Territories and one of the most amazing marine environments anywhere in the world. Located about 1,500km from the southern tip of India, 3,400km due east of Africa and 3,000km west of Indonesia the territory covers a total of 640,000km2 of ocean. At its heart is the Chagos archipelago, a scattering of 55 tiny islands surrounded by 60,000km2 of coral reefs and the cleanest seawater ever recorded. ZSL has been actively working in BIOT for more than 10 years and our efforts there are collaborative across our departments and with many other institutions globally.

Why we are there

The open ocean, tropical coral reefs and islands of the territory have a huge abundance of marine and terrestrial species. BIOT contains the largest living coral atoll anywhere on earth – the Great Chagos Bank, one of the few increasing breeding seabird colonies in the tropical Indian Ocean and eight times more reef fish biomass than anywhere else in the Indian Ocean [1].

BIOT teems with life, from large pelagic predators like thresher sharks, yellowfin tuna, huge pods of spinner dolphins, to abundant reef fish and seabirds. Whilst under pressure from threats such as climate change and illegal fishing, due to the remote location, exploitation of the reefs and pelagic wildlife is reduced and hence the abundance of wildlife found in BIOT still represents some of the best examples of these habitats left anywhere in the world.

The largest no-take Marine Reserve in the Indian Ocean

Over 275,000 people and a number of influential science and conservation organisations called on the UK Government to establish the territorial waters of the British Indian Ocean Territory as a Marine Reserve in 2010. ZSL was amongst the organisations that contributed to the science case for the creation of the reserve [2] and that helped to ensure its establishment. This decision was one of the most significant ways the UK could make a landmark contribution to global marine conservation and was part of the starting point for the Blue Belt programme where the UK government aims to protect over four million square kilometres of marine environment across the UK Overseas Territories. The designation also contributes greatly to a number of globally agreed targets, such as the IUCN World Conservation Congress target to protect 30% of each marine habitat in highly protected marine reserves by 2030.

The ‘no-take’ designation makes the 640,000km2 an IUCN Category 1 strict nature reserve meaning no extractive industries (fishing, mining, dredging) can take place. There is an exemption of a few miles around the island of Diego Garcia in the south which houses a military facility.

The future of the BIOT marine reserve

From 2010 to 2016 the BIOT marine reserve was the largest in the world. Since then it’s been overtaken by even bigger protected areas, some of them in other UK Overseas Territories such as the enormous Pitcairn Marine Reserve which is 834,000 km2. ZSL has played a key role in the creation of many of these new protected areas as well through its role in the Great British Oceans campaign.

Since 2010 ZSL has been working with many other organisations to better understand the astounding array of wildlife that lives in BIOT and has been making significant advances in marine science and conservation. We have worked closely with the BIOT administration in the Foreign and Commonwealth Office and with the Bertarelli Foundation to develop an ambitious programme of research to support ever better management of the marine reserve into the future.

A healthy Porites colony on the reef

ZSL work in BIOT

The Bertarelli Programme in Marine Science

In 2017 the Bertarelli Foundation announced its new programme for marine science in BIOT. The programme builds on a series of expeditions, workshops and strategic plans to create a vision for the BIOT marine reserve as a global exemplar of science and conservation activities working to support effective management. From 2017 to 2021 the programme will be coordinated on behalf of the foundation by ZSL and comprises a team of 50 researchers from 14 institutions across the world studying all aspects of the animals and habitats of this amazing place. For more information, please see the Bertarelli Programme in Marine Science tab above.

Reducing the impact of plastics on the BIOT natural environment

On the 1st April 2019 we will begin a new project funded by Darwin Plus, a UK government initiative, to focus on the impact of plastic waste on the BIOT natural environment. The accumulation of plastic debris pollutes BIOT’s coastal ecosystems negatively impacting biodiversity, including populations of (endangered) green and (critically endangered) hawksbill sea turtles. Working with our partners at Swansea University and the BIOT administration we will investigate the impacts of macro and micro plastics on nesting sea turtles and work to develop long term strategies to enable systematic change, to reduce single-use plastics consumption and improve disposal and recycling practices on Diego Garcia.

Connect Chagos: People and wildlife

As part of ZSL’s commitment to global and local conservation capacity building we designed a delivered a four year programme called Connect Chagos. This multi-phase project to build environmental skills and awareness within the Chagossian community in the UK and overseas was a great success and we learnt huge amount from working alongside each other. We continue to stay interested and involved in the communities are looking for ways to continue this work into the future.


[1] Graham N.A.J., Pratchett M.S., McClanahan T.R., Wilson S.K. (2013) The Status of Coral Reef Fish Assemblages in the Chagos Archipelago, with Implications for Protected Area Management and Climate Change. In: Sheppard C. (eds) Coral Reefs of the United Kingdom Overseas Territories. Coral Reefs of the World, vol 4. Springer, Dordrecht

[2] Koldewey, H.J., Curnick, D., Harding, S., Harrison, L.R. and Gollock, M. (2010) Potential benefits to fisheries and biodiversity of the Chagos Archipelago/ British Indian Ocean Territory as a no-take marine reserve. Marine Pollution Bulletin, 60 (11). pp 1906-1915

Project information

Key species

  • Turtles – green (Chelonia mydas) and hawksbill (Eretmochelys imbricata)
  • Seabirds – Boobys (Sula spp), Frigate (Fregata spp)
  • Pelagic predators - open ocean sharks, rays and tuna
  • Coral reef
  • Reef fish

People involved at ZSL

Dr Heather Koldewey is the Head of Marine and Freshwater Conservation

Rachel Jones is the Project Manager for the Bertarelli Programme in Marine Science

Emma Levy is the Project Administrator for the Bertarelli Programme in Marine Science

Partners and sponsors

The Bertarelli Programme in Marine Science is kindly supported by the Bertarelli Foundation.

Previous work in BIOT has been funded by: PEW Charitable Trusts; Darwin Initiative - Overseas Territories Challenge Fund; PEW Environment Group; Defra; Foreign and Commonwealth Office; Waterloo Foundation; Blue Marine Foundation;; University College London; Rufford Small Grants Foundation. 

Our partners include: Chagos Conservation Trust; Marine Resources Assessment Group; Centre for Environment, Fisheries and Aquaculture Science; Marine Management Organisation; University of Bangor; University of Western Australia; University College London;, University of Oxford; University of Exeter; University of Montpellier; Stanford University; Scottish Association of Marine Science; Natural History Museum; Deakin University; Manta Trust; University of Swansea; University of Lancaster; Australian Institute of Marine Science. 

The Bertarelli Programme in Marine Science is a highly collaborative programme bringing together experts from across the world to research and improve our understanding of how best to protect the ocean. The programme has identified projects which will take place between 2017 and 2021 to investigate a wide range of information from ecology, role and behaviour or target species to the impacts of illegal, unreported and unregulated fishing on the BIOT marine reserve.

The 9 science projects are grouped under three main themes:

Sentinel species

The team will be studying the ecology and distribution of large highly mobile animal species in the ecosystem – many of them top predators. These animals at the top of the food chain often drive the dynamics of populations below them and understanding where they are and what they are doing can unlock incredible insights into the whole ecosystem. It also helps to figure out where and when they might be most vulnerable to poaching which can help with better targeted enforcement efforts. Our sentinel species groups are:

  • Pelagic predators - open ocean sharks, rays and tuna
  • Reef sharks
  • Turtles
  • Seabirds

Coral reefs

There are at least 310 species of coral on the reefs of the Chagos Archipelago, including the Chagos brain coral (Ctenella chagius), a species endemic to these waters. Corals not only created the tiny atoll islands of the archipelago but dense populations of branching species continue to protect them from waves and storm damage. Corals on these reefs have been hit hard by bleaching from rising sea temperatures during the El Nino events of 2014 and 2017 with widespread mortality down to 15m. These reefs have been impacted like this before with similar widespread damage after the 1998 bleaching. Despite this knock-back, juvenile corals are already starting to grow on the old skeleton left behind by the dead adult colonies. The team will be closely studying their recovery and resilience over the next three years and trying to describe what the future may hold for these reefs.

comparison of reef health at Ile Anglais reef. Salomon Atoll. BIOT
Ile Anglais, Salomon Atoll reef in 2006 and in 2017 [1]
[1] Sheppard C, Sheppard A, Mogg A, Bayley D, Dempsey A, Roche R, Turner J, Purkis S. (2017) Coral Bleaching and mortality in the Chagos Archipelago. Atoll Research Bulletin. 613: 1-28. 

Illegal, unregulated and unreported fishing

Like any protected area the animals of BIOT are under threat from poachers, the sheer abundance of target species like tuna and shark make the territory very attractive to those who seek to benefit from breaking the rules. Understanding what drives fishers to break the rules, where they come from and how they work is key to figuring out how to better protect the biodiversity of the marine reserve. We will be conducting socio-economic studies across the region to inform management and ensure the reserve is well protected. 

By combining our work on both the fishers and the species that are fished we hope to contribute to improved protection of the reserve.


Over the course of the programme teams will be in the field several times each year and we will be bringing information live from each trip. 

Upcoming 2018 expeditions

January - February Seabird survey and tagging expedition
February - March

Array servicing and pelagic tagging expedition

March - April

Reef surveys (coral) expedition


Reef surveys (fish) expedition

June - July Turtle survey and tagging expedition
June - July Seabird survey and tagging expedition

Follow the programme on twitter at @BIOTscience and keep in touch with all the science going on in BIOT using #BIOTscience

Project Information

Contact BPMS:

People Involved

In the Institute of Zoology there are several researchers working on aspects of BIOT science:

David Curnick is investigating the role of large marine protected areas as a conservation strategy for pelagic tunas and sharks.

David Jacoby is studying the behaviour and ecology of reef sharks, a group of species under particular pressure from poaching activities.

Tom Letessier is working to understand how Illegal, Unreported and Unregulated (IUU) fishing impacts the marine reserve and how fishers that break the rules there perceive the risks and benefits of doing so.

Malcolm NicollRobin FreemanPeter Carr and Hannah Woods are all working on aspects of seabird biology and ecology across the region.


Kindly supported by the Bertarelli Foundation

Partners & Supporters:

Australian Institute of Marine Science

Bangor University

Deakin University

Lancaster University

Manta Trust

Scottish Association of Marine Science

Stanford University

Swansea University

University of Exeter

University of Oxford

University of Western Australia

Connect Chagos 2015

The Project 

The Connect Chagos Project was created in 2012 to engage with Chagossian communities based in the UK in order to increase environmental awareness and to contribute to the conservation of the Chagos Archipelago.

Staff from the Connect Chagos Project worked in Crawley and Manchester, hosting events such as Environmental Open Days and Tailored Sessions to actively engage with the community and to increase awareness of the extraordinary environment of the Archipelago.

Each summer an Environmental Training Course was run, in partnership with many conservation organisations, which covered a variety of nature-related topics from bird monitoring, habitat management and marine conservation. Individuals who successfully completed the training course were then invited to apply for bursaries to fund advanced training and to join a scientific expedition to the Chagos Archipelago.

From 2012 – 2015 the project actively engaged with >700 community members from Crawley and Manchester. 42 ambassadors completed the environmental training course, 19 of which went on to carry out advanced training which included chainsaw training and gaining SCUBA diving qualifications. 7 ambassadors have joined scientific expeditions and one individual has recently represented the community at a “Big Oceans” meeting in Hawaii. 

Connect Chagos 2015

The Connect Chagos Book

The book was created as a lasting legacy of the project and as a resouce for the community. It's colourful pages contain information on each of the topics covered during the training course. Starting with an "Introduction to Conservation" it not only educates the reader on the wonderful environment of the Chagos Archipelago but provides useful hints and tips for learning about our wildlife here in the UK. A PDF version can be downloaded below, or contact Kirsty Richards to be sent a hard copy.

PDF icon The Connect Chagos Book (5.36 MB)



Connect Chagos Environmental Training Course Film 2014.


Contact Connect Chagos:

Kirsty Richards

Connect Chagos : People & Wildlife 2014 Booklet

PDF icon Connect Chagos 2014 Booklet (9.49 MB)


Foreign and Commonwealth Office

Chagos Conservation Trust

Darwin Initiative

Partners & Supporters

Bangor University



Manchester Museum

Blue Ventures

Yu Diving

London School of Diving

The Deep Aquarium

The Horniman Museum

City of London

The Ness Botanical Gardens

Natural England

Sayers Croft