Tag: Seaturtle

Kimberley Stokes PhD.

Institution:
Swansea University

Profile

I am currently studying the depth use ecology of green and hawksbill turtles in the Chagos Archipelago.

The ability of sea turtle populations to rebound following adequate protection should inspire us all to do more to conserve the world’s remaining habitats for all species.

Kimberley Stokes

Biography

2021 Present
Postdoctoral Research, Swansea University
2014 2021
Maternity leave; collaborative research with University of Exeter
2009 2014
PhD research with University of Exeter; management of sea turtle conservation project in North Cyprus
2014 2014
Freelance work for Natural England
2012 2013
Research placement at Wave Hub Ltd, Hayle
2008 2009
Writer of species accounts for ‘EDGE’ of Existence, Zoological Society of London
2008 2008
Management of volunteers at Elephant Nature Park, Mae Tang Valley, Northern Thailand. Also worked at the Gibbon Rehabilitation Project, Phuket during this time.
2006 2007
MSc Ecology, Bangor University

My Project

  • Species Distribution and Ecology
    Conservation of Sea Turtles in the Indian Ocean Region
    More

Other interests

I also have a research interest in sea turtle nest incubation conditions, and the impact of micro- and macro-plastics in beach sediment.

My Publications

Optimization of Swim Depths Across Diverse Taxa Furing Horizontal Travel

Stokes, K.L., Esteban, N., Casale, P., Hays, G.C. (2024) Optimization of swim depths across diverse taxa during horizontal travel. PNAS

Assessing the Impacts of Satellite Tagging on Growth of Immature Hawksbill Turtles

Stokes, H.J., Stokes, K.L., Mortimer, J.A., Laloe, J-O., Esteban, N., Hays, G.C. (2024). Assessing the impacts of satellite tagging on growth of immature hawksbill turtles. Methods in Ecology and Evolution.

High Dive Efficiency in Shallow Water

Stokes, K.L., Esteban, N., Stokes, H.J., Hays, G.C. (2023). High dive efficiency in shallow water. Marine Biology.

Yadvinder Malhi
Audrey Jaeger
Asha de Vos
Lasuni Gule-Godage

Alex Rattray PhD.

Institution:
Deakin University

Profile

I am a marine ecologist interested in space-based management of ecosystems and the role that increasingly accurate and resolved tracking, and remote sensing technologies can play in informing environmental decision making that is effective in protecting species and their habitats.

My research focuses on combining satellite tracking with multi-scale environmental data to investigate the movement ecology of sea turtles in the western Indian Ocean.

Working closely with a team led by Prof. Graeme Hays and Dr Nicole Esteban our research is revealing the importance of the Chagos Archipelago to the greater WIO environment through identification of migratory routes and key foraging areas of both adult and juvenile green and hawksbill sea turtles.

High accuracy satellite tracking is showing that for some large marine vertebrates, even small protected areas of only a few km2 can encompass the movements of a large proportion of individuals over long periods.

Alex Rattray

Biography

2015 Present
Research Fellow, Deakin University, Australia
2013 2015
Research Fellow, University of Pisa, Italy
2009 2013
PhD, Deakin University, Australia

My Project

  • Species Distribution and Ecology
    Conservation of Sea Turtles in the Indian Ocean Region
    More

Other interests

My Publications

Remote Submerged Banks and Mesophotic Ecosystems Can Provide Key Habitat for Endangered Marine Megafauna

Hays, G.C., Laloë, J-O., Mortimer, J.A., Rattray, A., Tromp, J.J., Esteban, N. (2024). Remote submerged banks and mesophotic ecosystems can provide key habitat for endangered marine megafauna. Science Advances.

Individual Variation in Home-Range Across an Ocean Basin and Links to Habitat Quality and Management

Hays, G.C., Rattray, A., Shimada, T., Esteban, N. (2024). Individual variation in home-range across an ocean basin and links to habitat quality and management. Journal of Applied Ecology.

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.

Emma Levy
Nicole Esteban
Asha de Vos
Antony Knights
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Other Scientists

Prof.
Heather Koldewey
Programme Co-ordinator
Emma Levy
Fiona Llewellyn
Island Reef Connections

Reducing the Impacts of Plastic around the Indian Ocean Natural Environment

Principal Investigators
Project Manager
Rachel Jones
Dr.
Nicole Esteban
Other Scientists

Project Overview

Context

With ~8 million tonnes of plastic entering the ocean annually, lasting 100s of years, a combined approach of reduction and mitigation is required to address the issue of plastic pollution.

UN Ocean Decade Challenge

Understand and beat marine pollution

Funded by

The Chagos Archipelago's coastal ecosystems are threatened by the accumulation of large volumes of plastic debris.

Although remote, large volumes of plastic waste pollute the Chagos Archipelago’s coastlines, negatively impacting biodiversity including regionally important populations of green (Endangered) and hawksbill (Critically Endangered) sea turtles. Plastic waste builds up on beaches and includes bottles, caps, containers and abandoned, lost or otherwise discarded fishing gear (e.g. nets, floats, buoy, rope). Accumulated debris at the top of beaches and amongst vegetation obstructs access to turtle nesting sites. Plastic particles in sand may increase sand temperature during incubation of eggs, potentially affecting turtle hatchling sex ratios. Plastics may also cause mortality by entanglement and ingestion. Occasional beach cleans remove shoreline debris that returns rapidly through flows of plastic into Chagos from heavily populated areas across the Indian Ocean. Consumption of single-use plastic on Diego Garcia also creates waste streams that are hard to manage in this remote location.

This project will empower Chagos stakeholders to implement cleaning strategies on target beaches, mitigating the impacts of plastics on nesting turtles. We will investigate the impacts of macro and micro plastics on nesting sea turtles and work to develop long-term strategies to enable systemic change, reducing Diego Garcia’s single-use plastic consumption, improving disposal and recycling practices.

This project is also funded by a UK Government grant, the Darwin Plus Initiative.

We have observed accumulated beach debris impeding turtle nesting activities on a number of beaches in the Chagos Archipelago.

Nicole Esteban

Key Facts

40%
of all plastic made yearly is for single-use plastic
175
average number of SUP water bottles UK adults use per year
7
All 7 marine turtles are known to ingest marine debris

Publications

Big Brands Impact Small Islands: Sources of Plastic Pollution in a Remote and Protected Archipelago

Savage, J., Chamberlain, A., Fellows, M., Jones, R., Letessier, T.B., Llewellyn, F., Morritt, D., Rowcliffe, M., Koldewey, H. (2024). Big brands impact small islands: Sources of plastic pollution in a remote and protected archipelago. Marine Pollution Bulletin.

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

Plastics Dominate Beach Debris in a Remote Archipelago; Spatial Variations in Island Debris Accumulation Inform Targeted Beach Management

Hoare, V., Atchison Balmond, N., Hays, G.C., Jones, R., Koldewey, H., Laloë, J-O., Levy, E., Llewellyn, F., Morrall, H., Esteban, N. (2022). Plastics dominate beach debris in a remote archipelago; spatial variations in island debris accumulation inform targeted beach management. Marine Pollution Bulletin.

Species Distribution and Ecology

Conservation of Sea Turtles in the Indian Ocean Region

Principal Investigators
Dr.
Nicole Esteban
Prof.
Graeme Hays
Other Scientists

Project Overview

Context

Sea turtles are flagship species for the Chagos Archipelago in the Indian Ocean Region. 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.

UN Ocean Decade Challenge

Protect and restore ecosystems and biodiversity

Funded by

Our sea turtle research programme is investigating three aspects of sea turtles: their biology; behavior; and their role as habitat indicators.

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.

Green turtles (Chelonia mydas) have been observed making huge migrations across the Indian Ocean from the Chagos Archipelago.

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.

Prof. Graeme Hays

Key Facts

2
species of turtles found in the Chagos Archipelago
85,000
worldwide population of green turtles
23,000
worldwide population of hawksbill turtles

News

  • Remarkable increase in turtle numbers on uninhabited islands
    Discover more
  • Changing Ratios in Hawksbill and Green Sea-Turtle Hatchlings
    Discover more
  • Satellite Tracking Uncovers Green Turtles’ Ability to Travel Staggering Distances
    Discover more
  • Green turtle (Chelonia mydas) swimming towards seagrass.
  • Satellite tagged Green turtle (Chelonia mydas) released, Diego Garcia.
  • Immature seaturtle satellite tagged in Turtle Cove, Diego Garcia.
  • Resting Hawksbill turtle (Eretmochelys imbricata).
  • Green Turtle (Chelonia mydas).
  • Inquisitive Hawksbill turtle (Eretmochelys imbricata).
  • Hawksbill turtle (Eretmochelys imbricata) near coral colonized by crustose coralline algae.
  • Green Turtle (Chelonia mydas).

Publications

A Global Assessment of Microplastic Abundance and Characteristics on Marine Turtle Nesting Beaches

Botterell, Z.L.R., et al (includes Esteban, N., Hays, G.C., Mortimer, J.A.) (2025). A global assessment of microplastic abundance and characteristics on marine turtle nesting beaches. Marine Pollution Bulletin.

Low Growth Rates at High Population Densities in Sea Turtles

Mortimer, J.A., Esteban, N., Laloe, J.-O., Stokes, H.J., Tromp, J.J., Hays, G.C. (2025) Low growth rates at high population densities in sea turtles. Marine Biology. 

Status, Trends and Conservation of Global Sea Turtle Populations

Hays, G.C., Laloe, J.-O., Seminoff, J.A. (2025). Status, trends and conservation of global sea turtle populations. Nature Reviews Biodiversity 

Optimization of Swim Depths Across Diverse Taxa Furing Horizontal Travel

Stokes, K.L., Esteban, N., Casale, P., Hays, G.C. (2024) Optimization of swim depths across diverse taxa during horizontal travel. PNAS

Assessing the Impacts of Satellite Tagging on Growth of Immature Hawksbill Turtles

Stokes, H.J., Stokes, K.L., Mortimer, J.A., Laloe, J-O., Esteban, N., Hays, G.C. (2024). Assessing the impacts of satellite tagging on growth of immature hawksbill turtles. Methods in Ecology and Evolution.

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Nicole Esteban Ph.D., FHEA, MSc

Institution:
Swansea University

Profile

I am a marine ecologist interested in developing our understanding of animal movements within marine and coastal habitats; and applying that knowledge to development of appropriate conservation policies for effective protection of species and their habitats.

I have been studying sea turtles in the Chagos Archipelago since 2012, working closely with Professor Graeme Hays and Dr Jeanne Mortimer.

During 2012-2021, we satellite tracked 36 post-nesting green turtles (Chelonia mydas) using Fastloc – GPS telemetry and recorded a huge range in migrations, from 75 km within the MPA surrounding the Chagos Archipelago to >5000 km to distant foraging grounds on the east coast of Africa, including Mozambique, Kenya and Somalia. Our current work includes use of satellite telemetry and other technologies such as drones and loggers to increase our understanding of key nesting and foraging grounds for immature and adult stages of both green turtles and the critically endangered hawksbill turtle (Eretmochelys imbricata) in the Western Indian Ocean. We are also conducting long-term monitoring of sea turtle nesting and foraging populations in the Chagos Archipelago, including long-term records of sand temperature to assess likely sea turtle hatchling sex ratios and hatching success.

Our satellite tracking research in the Chagos Archipelago has led to incredible discoveries of extensive seagrass meadows on the Great Chagos Bank at unexpected depths of 25-30 metres – providing critical habitats for juvenile fish populations and foraging green turtles.

Nicole Esteban

Biography

2019 Present
Associate Professor in Marine Biology, Swansea University, UK
2017 2019
Research Fellow, Bioscience Department, Swansea University, UK
2011 2016
Part-time Ph.D. : Ecology of sea turtles in the Caribbean and Indian Ocean
2010 2017
SEACAMS Project Manager, Swansea University, UK
2003 2010
Marine and Terrestrial Park Manager, St Eustatius, Netherlands Antilles
2000 2003
Environmental Consultant, MRAG Ltd, London, UK
1998 1999
MSc. Tropical Coastal Management, Newcastle University, UK
1994 1998
BSc (Hons). Marine Biology, Swansea University, UK

My Project

  • Island Reef Connections
    Reducing the Impacts of Plastic around the Indian Ocean Natural Environment
    More
  • Species Distribution and Ecology
    Conservation of Sea Turtles in the Indian Ocean Region
    More

Other interests

Currently investigating the effects of macro- and microplastics on sea turtle incubation conditions using a range of field and controlled laboratory conditions. This research is funded by DEFRA Darwin Plus project (2019-2022): Reducing the impacts of plastic on the Chagos Archipelago natural environment.

My Publications

A Global Assessment of Microplastic Abundance and Characteristics on Marine Turtle Nesting Beaches

Botterell, Z.L.R., et al (includes Esteban, N., Hays, G.C., Mortimer, J.A.) (2025). A global assessment of microplastic abundance and characteristics on marine turtle nesting beaches. Marine Pollution Bulletin.

Low Growth Rates at High Population Densities in Sea Turtles

Mortimer, J.A., Esteban, N., Laloe, J.-O., Stokes, H.J., Tromp, J.J., Hays, G.C. (2025) Low growth rates at high population densities in sea turtles. Marine Biology. 

Optimization of Swim Depths Across Diverse Taxa Furing Horizontal Travel

Stokes, K.L., Esteban, N., Casale, P., Hays, G.C. (2024) Optimization of swim depths across diverse taxa during horizontal travel. PNAS

Assessing the Impacts of Satellite Tagging on Growth of Immature Hawksbill Turtles

Stokes, H.J., Stokes, K.L., Mortimer, J.A., Laloe, J-O., Esteban, N., Hays, G.C. (2024). Assessing the impacts of satellite tagging on growth of immature hawksbill turtles. Methods in Ecology and Evolution.

Empirical Evidence for the Extent of Spatial and Temporal Thermal Variation on Sea Turtle Nesting Beaches

Stokes, H.J., Laloe, J-O., Esteban, N., Hays, G.C. (2024). Empirical evidence for the extent of spatial and temporal thermal variation on sea turtle nesting beaches. Journal of Thermal Biology

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Peter Carr
Jacques-Olivier Laloë
Camilla Labonte
Claire Collins

Graeme Hays PhD.

Institution:
Deakin University

Profile

I am a marine ecologist with long standing interests in the use of satellite tracking to examine marine animal movements and the impacts of climate change on marine systems.

I am a marine ecologist with long standing interests in the use of satellite tracking to examine marine animal movements and the impacts of climate change on marine systems. Working closely with Dr Nicole Esteban, my current work in the Chagos Archipelago includes assessment of the movements of both adult and juvenile green and hawksbill turtles. The long-term tracks show that for green turtles, females nesting on Diego Garcia may migrate to foraging sites across the Western Indian Ocean and travel indirect routes to these targets indicting migrating turtles only have a relatively crude map sense in the open ocean (https://doi.org/10.1016/j.cub.2020.05.086). Compared to post-nesting green turtles, hawksbill turtles travel much shorter distances to foraging sites on the Great Chagos Bank and other banks in the region, showing the broader ecological importance of these little studied habitats.

Our long-term records of sand temperature on nesting beaches in the Chagos Archipelago have revealed that shading of nests by vegetation helps to reduce incubation temperatures, helping to ensure both fairly balanced hatchling sex ratios as well as high egg survival (http://dx.doi.org/10.1038/srep20339). Further, we have shown that sea turtle nests across the archipelago are fairly resilient to the marine heatwaves that have devastated coral reefs in the region (https://doi.org/10.1098/rsbl.2021.0038). Long-term monitoring shows encouraging upward trends in the annual number of nests (https://doi.org/10.1017/S0030605319001108).

Among the topics we are exploring in ongoing work are the diet of turtles, foraging turtle densities using drone surveys, nest site selection and the vulnerability of nesting areas to sea level change.

In 1873, Charles Darwin marvelled at the ability of sea turtles to find isolated island breeding sites, but how turtles navigate remains perplexing. Our satellite tracking work has helped solve this riddle, showing turtles can reorient in the open ocean, but only at a crude level.

Graeme Hays

Biography

2013 Present
Professor of Marine Science, Deakin University
2005 2015
Professor of Marine Biology, Swansea University

My Project

  • Species Distribution and Ecology
    Conservation of Sea Turtles in the Indian Ocean Region
    More

Other interests

I help to lead a collaborative global project (Megamove.org) to compare the patterns of movement across multiple taxa including sea turtles, sharks, marine mammals and birds including an assessment of the threats these animals face. Megamove has been endorsed by the UN Ocean Decade for Sustainable Development

My Publications

A Global Assessment of Microplastic Abundance and Characteristics on Marine Turtle Nesting Beaches

Botterell, Z.L.R., et al (includes Esteban, N., Hays, G.C., Mortimer, J.A.) (2025). A global assessment of microplastic abundance and characteristics on marine turtle nesting beaches. Marine Pollution Bulletin.

Low Growth Rates at High Population Densities in Sea Turtles

Mortimer, J.A., Esteban, N., Laloe, J.-O., Stokes, H.J., Tromp, J.J., Hays, G.C. (2025) Low growth rates at high population densities in sea turtles. Marine Biology. 

Status, Trends and Conservation of Global Sea Turtle Populations

Hays, G.C., Laloe, J.-O., Seminoff, J.A. (2025). Status, trends and conservation of global sea turtle populations. Nature Reviews Biodiversity 

Optimization of Swim Depths Across Diverse Taxa Furing Horizontal Travel

Stokes, K.L., Esteban, N., Casale, P., Hays, G.C. (2024) Optimization of swim depths across diverse taxa during horizontal travel. PNAS

Assessing the Impacts of Satellite Tagging on Growth of Immature Hawksbill Turtles

Stokes, H.J., Stokes, K.L., Mortimer, J.A., Laloe, J-O., Esteban, N., Hays, G.C. (2024). Assessing the impacts of satellite tagging on growth of immature hawksbill turtles. Methods in Ecology and Evolution.

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Jessica Savage
Philip Hosegood
Laurence Humeau
Daneeja Mawren