The Remote Chagos Archipelago

Image: A healthy coral reef scene in Chagos. Credit: Jon Slayer


This week the Catlin Seaview Survey is heading out to the remote Chagos Archipelago in the Indian Ocean, some 500 nautical miles south of the Republic of the Maldives, which itself is already over 300 nautical miles out to sea south of India. We will be leaving Australia a few days early, because the only way of getting to this remote atoll system, some 3,400 open sea miles east of Africa and 3,000 miles west of Indonesia, is by military aircraft, requiring more time for coordination.  We will be guests on the territory patrol vessel, called the Pacific Marlin, whose usual work is to conduct resource protection patrols, keeping the vast 644,000 square kilometer Fisheries Conservation and Management Zone free of illegal fishing. This vast area, which consists mostly of blue water but also includes 58 low sandy islands and hundreds of individual reefs, is nearly twice the size of Britain. Some areas were not even mapped until late in the 20th century, with the 1998 charts still having regions marked with dotted lines and the legends “existence doubtful” and “position approximate” on some features.


Taking a step back in time


This protected area, only established in 2010, is the largest no-take reserve anywhere in the world’s oceans, and in fact is nearly the size of all the other no-take reserves in the world added together. The largest single coral atoll in the world is located here, enclosing the Great Chagos Bank, which covers some 12,642 square kilometers. These are some of the healthiest and cleanest tropical reef systems anywhere on the planet. The local stressors so common and so damaging on coral reefs around the world are for the most part not present here, including overfishing of reef fish, wholesale removal of the top predators like sharks for international trade, discharge of raw sewage into the waters, and discarding plastics and other solid waste onto the reefs. However, this is not to say that the reefs of the Chagos Archipelago are unaffected by man, for the global stressors of sea surface temperature rise and ocean acidification are beginning to exert themselves here, like every other location in the biosphere. The Catlin Seaview Survey research mission here will be doing surveys and taking samples with this interesting dichotomy in mind -- that diving in this area will be like taking a step back in time to an era when reefs were thriving, but that we may still be looking at an underwater landscape already demonstrating the silent impacts of global change.


Anticipating a thriving ecosystem


There are few other places left on earth with thriving ecosystems that have been so little affected by humans as the Chagos Archipelago. We are anticipating that the coral cover, the abundance of sharks, the biomass of herbivores, and all other indications of ecosystem health will be superlative. What we hope to do is to observe and catalogue as much of this as we can on our small mission, and to bring these images to the online world in panoramic form, so that the rest of the world can also appreciate the wealth and value of these unique islands.