For Olivier Bancoult, of the Chagos Refugee Group, it was the sight of two skuas gliding over the waves that heralded long-promised landfall on his native islands.
During the first three days of the voyage from Seychelles there had been remarkably few seabirds, until the Mauritian-chartered Bleu De Nîmes, a cruise ship converted from its former use as a British minesweeper, neared the Chagos Islands.
Excitement began to build among the exiled Chagossians returning to their homeland. They played music on the quarterdeck. “I will be free,” said Rosemonde Bertin, throwing up her arms in anticipation of stepping ashore on Salomon Island, where she was born 67 years ago.
The captain sounded the ship’s horn as the vessel crossed into waters that the UK claims as British Indian Ocean Territory (BIOT), despite the United Nations having confirmed three years ago that the area legally belongs to Mauritius.
On the top deck, the Chagossians danced and sang in gentle, warm rain, raising glasses of champagne beside two open-air hot tubs.
After repeated recalculations of tides and headwinds, the ship was expecting to anchor on Saturday afternoon (local time) off Peros Banhos. The Chagossians will be among the first to set foot on the island.
They intend to plant a Mauritian flag and their own orange, black and blue Chagos banner – symbolising the sunset glowing when they were deported by British-chartered boats 50 years ago, the dark years of their exile and the blue ocean.
Flowers will be laid in the overgrown cemetery on the island where their ancestors lie. One photograph that has infuriated the exiles is of the studiously well-kept military animal graveyard on the UK/US base on nearby Diego Garcia. The decay of their families’ cemetery on Peros Banhos seems cruel by comparison.
The voyage’s main scientific purpose is to place underwater tide gauges on the sea floor on the outlying Blenheim Reef. That is likely to be done early on Sunday. The devices will measure sea levels and enable Swedish experts on the ship to calculate whether any of the reef remains above water at what is known as “highest astronomical tide”.
Ola Oskarsson, a marine surveyor retained by Mauritius, is leading the project. If he finds that any part of Blenheim Reef – even a small rock or shingle beach – stays dry all the time, then that can be used as a new outer base point for extending a 200-mile exclusive economic zone (EEZ) in legal argument under the UN convention on the law of the sea.
The work, to resolve maritime boundaries with neighbouring Maldives, is being undertaken by Mauritius in the expectation that it will at some point regain control of the Chagos Islands from the UK.
The Foreign, Commonwealth and Development Office has promised “it would not interrupt the survey”. Whether Mauritian activity and landings within what is claimed as BIOT will be monitored by British officials is unclear. In Mauritius itself there has been media criticism of the cost of the expedition and complaints that not enough Mauritian journalists were invited on to the ship.
The strangest fact to emerge during the voyage, however, is that the seas around the Chagos archipelago are almost 100-metres below average sea levels elsewhere around the globe.
That extraordinary marine feature is due to the Earth not being a perfect sphere but more like a lumpy potato. Different densities inside our planet cause fluctuations in gravity, which affect the behaviour of the oceans.
“Mean sea level is not constant,” explained Oskarsson. “It’s undulating because of gravity. Water shifts to even out irregularities.” The Chagos Islands are on a slope that bottoms out at the Maldives.
Pravind Jugnauth, prime minister of Mauritius, told the Guardian in a telephone call that organising his country’s first expedition to the Chagos Islands was “not in any way a hostile act”. “It is not in any way meant to embarrass the UK. It is merely an exercise of our sovereignty over part of our territory and that is in accordance with international law.”
“We totally condemn the way that the Chagossians have been treated by the UK. Uprooting people from their place of birth and where they were living without any warning and putting them on a ship and just leaving them at the quay in Mauritius and preventing them from going back – that clearly a crime against humanity and it’s extraordinarily serious.”
A UK Foreign Office spokesperson said: “The UK has no doubt as to our sovereignty over the British Indian Ocean Territory. Mauritius notified the UK about its plans to conduct a scientific survey close to the Chagos islands. The UK shares this interest in research and environmental protection and gave assurances to Mauritius that it would not interrupt the survey.”