Sliteye shark discovered in remote Indian Ocean: Rare predator spotted for the first time in Chagos waters

An image of a sliteye shark swimming around a bait box. (Image: Charlotte Oulton)

For the first time, scientists have recorded the sliteye shark in the Great Chagos Bank, the world’s largest coral atoll. The discovery highlights the hidden biodiversity of the Chagos Archipelago and its Marine Protected Area.

First record of sliteye shark in Chagos
The shark, named for its narrow slit-like eyes, was captured on camera in deep seagrass habitats on the southern rim of the Bank. Researchers recorded two individuals just 11 kilometres apart at depths of 23 to 29 metres using Baited Remote Underwater Video systems. The species is usually found in deeper waters, but it also adapts well to shallow clear seas.

New insights into deepwater seagrass habitats
These findings shed light on seagrass ecosystems first mapped in 2016 after satellite tracking of green turtles revealed meadows far deeper than expected. Since then, more than 110 fish species have been observed using these underwater grasslands for food and shelter. Scientists now know that sliteye sharks also depend on these habitats.

Charlotte Oulton, a researcher at Swansea University, said the discovery was both exciting and significant, pointing to how little is known about deepwater seagrass systems. Dr Nicole Esteban, also from Swansea, said the research shows the crucial role of these meadows in supporting marine biodiversity in the Indian Ocean.

Conservation concerns for a declining species
Listed as near-threatened, sliteye shark numbers are projected to decline by nearly 30% within 15 years due to heavy fishing pressure. The discovery in Chagos raises important questions about its abundance, habitat use, and conservation needs. Scientists say the results strengthen the case for protecting deepwater seagrass habitats in the Indian Ocean.

The study forms part of a project led by Swansea University with international partners, funded by the Bertarelli Foundation. Full findings are due in 2026.