Population genetics of green (Chelonia mydas) and hawksbill turtles (Eretmochelys imbricata) in Grenada, West Indies

Delivering evidence to inform future management decisions by the Grenadian government and assist in the conservation of sea turtle populations
A hawksbill sea turtle (Eretmochelys imbricata) - picture by Kate Charles, Ocean Spirits Inc
Title: Population genetics of green (Chelonia mydas) and hawksbill turtles (Eretmochelys imbricata) in Grenada, West Indies
Funded by: Oscar Montgomery Environmental Foundation (OMEF), Windward Islands Research and Education Foundation (WINDREF), Sandals Foundation, SEE Turtles.
Duration: 2022–2024 
Investigators: ResM student Naomi Westlake, Kate Charles (Ocean Spirits Inc.), Dr Brian Shamblin (University of Georgia), Jonnel Edwards (St. George’s University), Dr Kenrith Carter (Ocean Spirits Inc.), Professor Martin Attrill (University of Plymouth), Dr David Marancik (St. George's University), Dr Clare Embling (University of Plymouth).
Research partners: St George's University, Ocean Spirits Inc., University of Georgia.
All research activities by Ocean Spirits Inc. are carried out under governmental research permits provided by the Grenada Fisheries Division.

A keystone species in decline

For over 100 million years, sea turtles in the West Indies have maintained seagrass beds and coral reefs by balancing marine food webs and nutrient cycles. The health of the ocean itself depends on this keystone species. 
Grenada's sea turtle populations are believed to be in decline due to illegal and legal harvests (including the seven-month legal harvest season in Grenada). A decline in their numbers directly affects biodiversity and the overall health of the environment and they are also an important component of ecotourism in Grenada – a symbol of cultural identity. 
A lack of detailed knowledge of the genetic make-up, life history and migration patterns of the local aggregates of these species currently limits conservation strategies for green and hawksbill turtles in Grenada. Through this international partnership, this project delivered important evidence to help inform future management decisions by the Grenadian government and assist in the conservation of sea turtle populations.
Naomi Westlake
Naomi Westlake, final samples
Naomi Westlake working in the laboratory.

Genetic characterisation

The research team identified the possible origins and migration corridors of Grenada's critically endangered hawksbill sea turtles and endangered green sea turtles by carrying out DNA analyses and assessing genetic connectivity with other populations. They also monitored nesting activities, as well as the overall health of each turtle sampled.
Genetic characterisation was used as a way to infer population diversity and to assess potential impacts from management strategies both regionally and worldwide.
Combined with serology, genetics was also used to understand the prevalence and spread of chelonid alphaherpesvirus-5 (ChHV5) and ChHV5-associated fibropapillomatosis, both of which have been reported within Grenada's green turtle population and in other populations in the Atlantic region.
Data revealed seven haplotypes within Grenada's foraging green turtle population, and a total of seven haplotypes across Grenada's nesting and foraging hawksbill turtle populations.

Shared resources, regional conservation strategies

Researchers identified Grenada's Isle de Caille hawksbill turtle rookery as a nesting population of origin for haplotype Ei-A68, which was an orphan haplotype prior to this study. In addition, two other rare hawksbill turtle haplotypes (Ei-A45, Ei-A72) were identified, as well as a new green turtle haplotype (CM.A82.1). Mixed stock analyses indicated that Grenada's green and hawksbill turtle populations are associated with a total of 15 other countries throughout the Atlantic region.
The research team observed no external fibropapillomatosis tumours on any green turtles during the study. However, ChHV5-specific antibodies were identified in blood serum in 9.38% of the green turtles sampled. There was no apparent association of ChHV5 serology status and green turtle haplotype, suggesting that all haplotypes were at equal risk of infection.
These findings strongly indicate that Grenada's sea turtle populations are regionally shared resources and should be managed as such. The rare and/or unique haplotypes present within Grenada's sea turtle populations offer valuable genetic diversity to the wider region, and further conservation strategies are warranted to protect these at-risk haplotypes. The researchers argue that this could involve incorporating Grenada’s populations into existing Regional Management Units (RMUs), or introducing new and/or amending existing legislation in Grenada.

Working to understand and protect endangered sea turtles

Discover ResM student, Naomi Westlake's journey in Grenada. 
Find out more about the research she carried out in the field and lab, meeting organisations and people who encounter the endangered turtle species on a daily basis.
Naomi Westlake on a boat in diving gear

The Marine Biology and Ecology Research Centre (MBERC)

Members of the MBERC address a broad range of research questions, from the effects of environmental stress on microbes and developing embryos to the management of large scale impacts, such as global climate change.
 
Students in the national marine aquarium looking at fish in a big tank