Rare sliteye shark discovered in remote Indian Ocean by Welsh university researchers

Researchers at a Welsh university have recorded the first-ever sighting of rare sliteye sharks in the Chagos Archipelago – marking a major milestone in marine biodiversity research.

The sliteye shark was recorded by Swansea University academics for the first time on the Great Chagos Bank – the world’s largest coral atoll structure.

Academics say it marks a major advance in understanding the geographic range of this near-threatened species.

Seagrass

The recent sightings in deepwater seagrass meadows remote underscore the ecological importance of the Chagos Archipelago and its Marine Protected Area, revealing previously undiscovered biodiversity in its reefs and seagrass beds.

Named for its distinctive, slit-like eyes – thought to enhance vision in low-light conditions – the sliteye shark is well adapted to deeper, dimly lit environments as well as clear, shallow water.

The sightings occurred in previously unstudied seagrass on the southern rim of the Great Chagos Bank.

The sharks were captured just 11 km apart, at depths of 23-29 metres, using Baited Remote Underwater Video (BRUV) systems – underwater survey systems that attract and record marine life without human disturbance.

These observations offer new insights into deepwater seagrass habitats first discovered by the team in 2016.

Discovery

Given the species’ wide distribution, researchers believe it’s unlikely that it is rare in Chagos.

Charlotte Oulton, study lead and Master’s by Research student in the Marine and Conservation Ecology Lab at Swansea University, said: “Discovering the sliteye shark in the Chagos Archipelago was incredibly exciting.

“Not only is it a new record for the region, but it also highlights how much we still have to learn about deepwater seagrass ecosystems and their role in supporting marine biodiversity, particularly in remote regions of the Indian Ocean.”

Dr Nicole Esteban, Associate Professor in Marine Ecology at Swansea University, added: “Satellite tracking of green turtles led us to discover extensive seagrass meadows on the Great Chagos Bank at depths of 25–30 metres – far deeper than expected.

“We have now recorded a wide diversity of marine life using this seagrass habitat for shelter and food, including over 110 fish species, and as we now know, the sliteye shark.”

With sliteye shark populations projected to decline by up to 29% in the next 15 years due to fishing pressures, the discovery raises questions about species abundance, habitat use, and conservation priorities.

Academics say it also reinforces the urgent need to explore and protect deepwater habitats.

The latest findings, based on surveys conducted in late 2024, are part of a collaborative project between Swansea University and international partners, funded by the Bertarelli Foundation through the Bertarelli Foundation’s Indian Ocean Marine Science Programme.

The research aims to map current seagrass coverage, model habitat suitability to predict the likely extent of seagrass growth and assess the ecological importance of deepwater seagrass ecosystems across the Archipelago.

Full findings are expected to be published in 2026.