The Ecology of Sea Turtles in the Indian Ocean Region
We use high-resolution satellite tracking of adult nesting female sea turtles to investigate their use of inter-nesting and foraging habitats within and beyond the MPA. These data are helping us to understand the turtles’ long-distance movements and identify any threats to their survival from outside the boundary of the reserve.
For juvenile foraging turtles, which tend not to travel such long distances, we are able to use these tracking data to assess their habitat use around Diego Garcia.
We track juvenile turtles by capturing animals in Diego Garcia’s lagoon and attaching tags to the carapace with quick setting epoxy. For breeding adults, we work on the nesting beaches on the ocean side of Diego Garcia using the same tagging technique. The resulting tag attachment is very low profile and streamlined so it has minimal impact on the turtle.
While all sea turtles nest on sandy beaches, at the end of the breeding season each species then travels to its preferred habitat – seagrass beds in the case of green turtles, and reef habitat for hawksbill turtles. Therefore, as well as identifying key zones for conservation, our high-resolution tracking work has the added value of also helping to identify the location of these important habitats. Throughout the project, we will use our network of collaborators to validate the use of sea turtles as habitat indicators across the Western Indian Ocean.
Estimating the absolute number of individuals in populations and their fecundity is central to understanding the ecosystem role of species and their population dynamics. Having an accurate population estimate allows conservation managers to make informed management decisions for endangered species such as sea turtles. The size of sea turtle populations is typically cited as the number of breeding females in a given year, estimates of which are made by counting tracks on nesting beaches which, when collected over many years, reveal trends in abundance and can be used to underpin species conservation decisions.
The population status of hawksbill and green turtles in the region surrounding the Chagos Archipelago is based on single visits and is calculated using many assumptions. Improved population estimates will be made through the use of historic and ongoing capture-mark-recapture studies of immature foraging turtles initiated in 1996 on Diego Garcia and combined with observational and turtle tracking data.
Turtles nesting in the Chagos Archipelago may conduct migrations of many thousands of kilometers; the MPA is therefore providing an important nesting sanctuary for turtles from across the entire Western Indian Ocean.
Remarkable increase in turtle numbers on uninhabited islands
Changing Ratios in Hawksbill and Green Sea-Turtle Hatchlings
Satellite Tracking Uncovers Green Turtles’ Ability to Travel Staggering Distances
Travel routes to remote ocean targets reveal the map sense resolution for a marine migrant
Hays, G.C., Atchison-Balmond, N., Cerritelli, G., Laloë, J.O., Luschi, P., Mortimer, J.A., Rattray, A., and Esteban, N., (2022) Travel routes to remote ocean targets reveal the map sense resolution for a marine migrant. Journal of the Royal Society Interface
Open Ocean Reorientation and Challenges of Island Finding by Sea Turtles During Long-Distance Migration
Hays, G.C., Cerritelli, G., Esteban, N., Rattary, A. and Luschi, P. (2020) Open ocean reorientation and challenges of island finding by sea turtles during long-distance migration. Current Biology.
Addressing Tagging Location Bias to Assess Space Use by Marine Animals
Hays, G.C., Rattray, A. and Esteban, N. (2020) Addressing tagging location bias to assess space use by marine animals. Journal of Applied Ecology.
Fidelity to Foraging Sites After Long Migrations
Shimada, T., Limpus, C. J., Hamann, M., Bell, I., Esteban, N., Groom, R. and Hays, G. C. (2020). Fidelity to foraging sites after long migrations. Journal of Animal Ecology
Estimates of Marine Turtle Nesting Populations in the South-West Indian Ocean Indicate the Importance of the Chagos Archipelago
Mortimer, J.A., Esteban, N., Guzman, A.N and Hays, G.C. (2020) Estimates of marine turtle nesting populations in the south-west Indian Ocean indicate the importance of the Chagos Archipelago. Oryx.