The waters around the Chagos Archipelago have long been marketed as one of the ocean's last untouched wildernesses. A new study argues the records underpinning that image are badly incomplete -- and that real fishing activity has been running at roughly 25 times the officially reported level.
Writing in the Journal of the Indian Ocean Region, a team from the Sea Around Us initiative rebuilt catch estimates for the archipelago going back to 1950. Rather than rely on the sparse official logs, they cross-referenced food-consumption figures, coconut-plantation employment records, distant-water fishing fleet data and declassified CIA documents to work out what was really being taken.
The heaviest toll came from industrial foreign fleets. Vessels from Japan, South Korea, Taiwan and the Soviet Union chased tuna across the region for decades, and their catches rose from about 100 tonnes in the 1950s to as much as 17,000 tonnes a year around the turn of the century. Local subsistence and recreational fishing, meanwhile, averaged some 100 tonnes annually -- a figure the official record understated 25-fold.
"But there is more to the story," said Dirk Zeller, the study's lead author and director of Sea Around Us - Indian Ocean at the University of Western Australia. "Historically, the UK only reported these catches, but prior to the 1970s, people working in the coconut plantations that operated in the atolls since the 1700s fished for subsistence."
Co-author Roshni Mangar, a Mauritian researcher at the University of British Columbia, said foreign boats had been a fixture far longer than most assume. "Mauritian commercial fisheries target mostly groupers, sky emperors and redfish, but we also found that there has been a presence of foreign DWF vessels in the region since the 1950s, targeting tuna and tuna-like species," she said.
Enforcement remains the sticking point. A no-take Marine Protected Area has covered the archipelago's exclusive economic zone since 2010, yet the researchers estimate illegal fishing still runs at about 600 tonnes a year, with Taiwanese and Sri Lankan vessels recorded targeting sharks and sea cucumbers.
"The limited patrols have inadequate deterrent effects and, unfortunately, these illegal catches, although relatively low, do pose a biodiversity risk to the MPA," Zeller said.
The timing matters. Britain agreed in May 2025 to transfer sovereignty of the Chagos to Mauritius while keeping the Diego Garcia base under a 101 million pounds-a-year arrangement, and there are already proposals to reopen parts of the protected zone to fishing. The authors say the missing history needs to be reckoned with first.
"This is why, in addition to patrols, vessel monitoring systems, port controls, regulatory sanctions and flag-state collaborations should be implemented once the territory's transfer is finalized," Mangar said.