Sliteye shark recorded in the Chagos for the first time!

The sliteye shark has been recorded for the first time on the Great Chagos Bank, the world’s largest coral atoll structure, marking a major advance in understanding the geographic range of this near-threatened species.

The recent sightings in deepwater seagrass meadows 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 - Loxodon macrorhinus - is well adapted to deeper, dimly lit environments as well as clear, shallow water like the 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 systems - underwater survey systems that attract and record marine life without human disturbance - deployed by the BIOT Senior Fisheries Protection Officer during regular patrols aboard the BIOT Patrol Vessel BPV).

Charlotte Oulton, study lead and Master’s by Research student in the Marine and Conservation Ecology Lab at Swansea University where CCT's interns are based, said: “This 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 and CCT Trustee said: “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 the sliteye shark.”

With sliteye shark populations projected to decline by up to 29% in the next 15 years due to fishing pressures, this discovery raises important questions about species abundance, habitat use, and conservation priorities. It also reinforces the urgent need to explore and protect deepwater habitats.

These 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.