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Green turtles continue to bounce back at a UNESCO site after half a century of protection

Updated: Sep 1, 2022

By Nancy Bunbury, on behalf of a group of co-authors from the University of Exeter and the Seychelles Islands Foundation

Turtles in Aldabra’s lagoon. (©Martin van Rooyen)

For anyone lucky enough to spend time on Aldabra, a remote, UNESCO-inscribed atoll in the Indian Ocean, one of the most striking first impressions is that “there are turtles EVERYWHERE”! New staff and visitors often cannot comprehend the sheer number of turtles they see by boat or when in the water. This wasn’t always the case: Aldabra’s green turtles were massively exploited in the early 20th century, and numbers declined precipitously, but in 1968 the site became the first in the Western Indian Ocean to protect turtles. Fast forward half a century and Aldabra now has the second largest breeding population in the region. But how much has it grown? A new paper published this week in Endangered Species Research by researchers from the University of Exeter and the Seychelles Islands Foundation explores the increase and identifies which parts of the atoll have seen the most growth.

Green turtle nesting on Aldabra. (©Richard Baxter)

The paper is the result of a fantastic collaboration based on an MSc project by University of Exeter student Adam Pritchard, supervised by Brendan Godley and co-supervised by SIF staff. Adam did a desk-based MSc project and was sent mountains of data from Aldabra (data from >44,000 turtle track surveys across Aldabra’s six beach groups during 1980–2019; >128,000 turtle tracks!). It was a daunting task; Adam and Aldabra staff spent months cleaning it, and overcame many data-related hurdles before the actual analysis could start. The results were clear – green turtle egg clutches increased by 410–665% since 1968 (based on historic estimates for that time), equating to an overall increase of ~2.6% per year, with an estimated 3059–5099 female turtles nesting at Aldabra today. Notably, the greatest increase was seen at the 2-km long Settlement Beach, which was not only the longest beach on the atoll but was, historically, the focal area for harvesting nesting turtles.

Picard island, Aldabra, showing Settlement Beach, the longest beach on the atoll, where turtles are making a remarkable comeback (©Martin van Rooyen)

With green turtles still being listed as Endangered by the IUCN, and having suffered massive historical population declines across their range, it’s great to be able to write about a ‘good news’ story, but there is another positive side to it…

Aldabra’s turtle track monitoring programme is the region’s longest-running, thanks largely to turtle legend Dr Jeanne A. Mortimer, who set up the programme and maintained the data for many years. Long-term monitoring takes decades of commitment, and often hundreds of field staff to collect the data. Organisations like SIF, with the enormous demands of running World Heritage sites and many parallel projects, are often not in a position (time- or skill-wise) to analyse the large datasets we produce, despite this being crucial to understand how effective our management is. SIF are therefore increasingly enlisting MSc students to address key research questions, focussing on data analysis gaps which cannot be filled on site. This is a win-win situation – students get to work with ‘real’ long-term data, often on iconic species, strengthen their data management and analysis skills, and can tackle important questions that have a genuine and immediate conservation impact on the ground, while NGOs receive the much-needed support to analyse datasets that might otherwise take years, and increase chances of peer-reviewed publication, which is viewed as the ‘gold standard’ at a practitioner level.

Local turtle expert, Dr Jeanne A. Mortimer with a green turtle on Aldabra (©Foto Natura).

So, to students looking for projects, please consider taking on a data analysis project with an NGO and throwing yourself into developing your analysis skills however daunting and ‘dry’ this might seem – not only will you upskill yourself in an area which is hugely lacking in conservation practice but it really does make a difference.

How many turtle tracks? SIF staff member ‘decoding’ turtle tracks on Aldabra (©Richard Baxter).

A parting thought: with Aldabra’s green turtle population still growing rapidly, how much bigger is it likely to get? Well, the numbers are still well below pre-exploitation estimates of ca. 6000–8000 females annually in early 1900s, so the increase will surely continue. In time this may provide the enormous privilege of a glimpse into what historical populations looked like, when the main population limiting factor was the high density of nesting turtles digging up each other’s eggs in their own enthusiastic bid to breed.
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