The Ecology of Sea Turtles in the British Indian Ocean Territory
Project Overview
Context
Sea turtles are flagship species for the British Indian Ocean Territory. Two species, hawksbill and green turtles, spend part or all of their immature and adult life stages in the Archipelago, using seagrass and coral reef habitats as foraging grounds. Nesting has been recorded across all islands on the five islanded atolls.
Funded by
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 British Indian Ocean Territory 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 BIOT 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.
Key Facts
News
Publications
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.
Green Turtle Diet is Dominated by Seagrass in the Western Indian Ocean Except Amongst Gravid Females
Stokes, H. J., Mortimer, J. A., Hays, G. C., Unsworth, R. K., Laloë, J. O., & Esteban, N. (2019). Green turtle diet is dominated by seagrass in the Western Indian Ocean except amongst gravid females. Marine Biology, 166(10), 135.
Drones for Research on Sea Turtles and Other Marine Vertebrates – A Review
Schofield, G., Esteban, N., Katselidis, K. A., & Hays, G. C. (2019). Drones for research on sea turtles and other marine vertebrates–A review. Biological Conservation, 238, 108214.
Convergence of Marine Megafauna Movement Patterns in Coastal and Open Oceans
Sequeira, A. M., Rodríguez, J. P., Eguíluz, V. M., Harcourt, R., Hindell, M., Sims, D. W., … & Hays, G. C. (2018). Convergence of marine megafauna movement patterns in coastal and open oceans. Proceedings of the National Academy of Sciences, 115(12), 3072-3077.
Satellite Tracking Sea Turtles: Opportunities and Challenges to Address Key Questions
Hays, G. C., & Hawkes, L. A. (2018). Satellite Tracking Sea turtles: opportunities and challenges to address key questions. Frontiers in Marine Science, 5, 432.
New Tools to Identify the Location of Seagrass Meadows: Marine Grazers as Habitat Indicators
Hays, G. C., Alcoverro, T., Christianen, M. J., Duarte, C. M., Hamann, M., Macreadie, P. I., … & York, P. H. (2018). New tools to identify the location of seagrass meadows: marine grazers as habitat indicators. Frontiers in Marine Science, 5, 9.
The Discovery of Deep-Water Seagrass Meadows in a Pristine Indian Ocean Wilderness Revealed by Tracking Green Turtles
Esteban, N., Unsworth, R. K. F., Gourlay, J. B. Q., & Hays, G. C. (2018). The discovery of deep-water seagrass meadows in a pristine Indian Ocean wilderness revealed by tracking green turtles. Marine pollution bulletin, 134, 99-105.
Fastloc-GPS reveals daytime departure and arrival during long-distance migration and the use of different resting strategies in sea turtles.
Dujon, A. M., Schofield, G., Lester, R. E., Esteban, N., & Hays, G. C. (2017). Fastloc-GPS reveals daytime departure and arrival during long-distance migration and the use of different resting strategies in sea turtles. Marine biology, 164(9), 187.
Diel and seasonal patterns in activity and home range size of green turtles on their foraging grounds revealed by extended Fastloc-GPS tracking
Christiansen, F., Esteban, N., Mortimer, J. A., Dujon, A. M., & Hays, G. C. (2017). Diel and seasonal patterns in activity and home range size of green turtles on their foraging grounds revealed by extended Fastloc-GPS tracking. Marine biology, 164(1), 10.
Implications of Location Accuracy and Data Volume for Home Range Estimation and Fine-Scale Movement Analysis: Comparing Argos and Fastloc-GPS Tracking Data
Thomson, J. A., Börger, L. & Christianen, M. J. A., Esteban, N. J., Laloë, J. O., Hays, G. C. (2017). Implications of location accuracy and data volume for home range estimation and fine-scale movement analysis: comparing Argos and Fastloc-GPS tracking data. Marine Biology. 164(10):204.
How Numbers of Nesting Sea Turtles can be Overestimated by Nearly a Factor of Two
Esteban, N., Mortimer, J. A., & Hays, G. C. (2017). How numbers of nesting sea turtles can be overestimated by nearly a factor of two. Proceedings of the Royal Society B: Biological Sciences, 284(1849), 20162581.
Male Hatchling Production in Sea Turtles from One of the World’s Largest Marine Protected Areas, the Chagos Archipelago
Esteban, N., Laloë, J. O., Mortimer, J. A., Guzman, A. N., & Hays, G. C. (2016). Male hatchling production in sea turtles from one of the world’s largest marine protected areas, the Chagos Archipelago. Scientific reports, 6, 20339.
Use of long-distance migration patterns of an endangered species to inform conservation planning for the world’s largest marine protected area
Hays, G. C., Mortimer, J. A., Ierodiaconou, D., & Esteban, N. (2014). Use of long‐distance migration patterns of an endangered species to inform conservation planning for the world’s largest marine protected area. Conservation Biology, 28(6), 1636-1644.