# Atlantic-wide connectivity of Ascension Island green turtles revealed by finer-scale mitochondrial DNA markers

## TL;DR

This study uses genetic markers to show how green turtles from Ascension Island connect with other populations across the Atlantic, highlighting the need for international conservation efforts.

## Contribution

The study introduces high-resolution mitochondrial DNA markers to reveal finer-scale genetic connectivity among Atlantic green turtle populations.

## Key findings

- Ascension Island contributes significantly to foraging aggregations in the Southwest Atlantic and Central Africa.
- Three main genetic groups were identified: Northwest Atlantic, Northern South America, and South and East Atlantic.
- Green turtles in the South and East Atlantic face threats from fishery bycatch.

## Abstract

Marine turtles undertake long migrations across different geographies and habitats, exposing them to a wide range of threats throughout their lifespan. Analysing population structure and connectivity is key to informing effective conservation management. We expand knowledge of Atlantic-wide connectivity of green turtles (Chelonia mydas) by characterising the genetic structure of the Ascension Island nesting population, one of the largest in the Atlantic Ocean, and carrying out Atlantic population structure and mixed stock analyses using high-resolution genetic markers. We amplified a ~ 738 bp fragment (extended D-loop) and a highly polymorphic mitochondrial short tandem repeat (mtSTR) fragment of the mitochondrial DNA control region, designating haplotypes based on (1) extended D-loop and (2) the extended D-loop and mtSTR combined. Overall, 11 extended D-loop and 33 combined haplotypes were found, the dominant haplotypes being CM-A8.1 and CM-A8.1/7-12-4-4. Population structure analysis found three main genetic groups: Northwest Atlantic, Northern South America, and South and East Atlantic. Mixed stock analyses indicate Ascension Island as a major source for juvenile foraging aggregations in the Southwest Atlantic (34–55%) and Central Africa (18–78%), with some contribution to West Africa (3–20%). Green turtles are vulnerable to fishery bycatch in the coastal waters of the South and East Atlantic. Our study underlines how improving sample sizes of Atlantic mtSTR haplotypes could further elucidate green turtle connectivity across threatened regions. We urge international collaboration to minimise mtSTR data gaps, in order to enhance connectivity assessments and improve conservation measures between countries that share populations.

The online version contains supplementary material available at 10.1007/s10592-025-01720-3.