Abstract
A solid understanding of the spatial ecology of green turtles (Chelonia mydas) is fundamental to their effective conservation. Yet this species, like many marine migratory species, is challenging to monitor and manage because they utilise a variety of habitats that span wide spatio-temporal scales. To further elucidate the connectivity between green turtle rookeries and foraging populations, we sequenced the mtDNA control region of 278 turtles across three foraging sites from the northern Great Barrier Reef (GBR) spanning more than 330 km: Cockle Bay, Green Island and Low Isles. This was performed with a newly developed assay, which targets a longer fragment of mtDNA than previous studies. We used a mixed stock analysis (MSA), which utilises genetic data to estimate the relative proportion of genetically distinct breeding populations found at a given foraging ground. Haplotype and nucleotide diversity was also assessed. A total of 35 haplotypes were identified across all sites, 13 of which had not been found previously in any rookery. The MSA showed that the northern GBR (nGBR), Coral Sea (CS), southern GBR (sGBR) and New Caledonia (NC) stocks supplied the bulk of the turtles at all three sites, with small contributions from other rookeries in the region. Stock contribution shifted gradually from north to south, although sGBR/CS stock dominated at all three sites. The major change in composition occured between Cockle Bay and Low Isles. Our findings, together with other recent studies in this field, show that stock composition shifts with latitude as a natural progression along a coastal gradient. This phenomenon is likely to be the result of ocean currents influencing both post-hatchling dispersal and subsequent juvenile recruitment to diverse coastal foraging sites.
Highlights
Migratory marine mega vertebrates are often long lived and utilise a variety of habitats that span wide spatio-temporal scales
Green Island (GI) (16◦45 S, 145◦58 E), a coral cay located in the northern Great Barrier Reef (GBR) region approximately 27 km offshore from Cairns, Queensland was sampled in October 2012
The most common haplotype observed was CmP47.1 at all three sites; Cockle Bay (CB) (73%), GI (67%) and Low Isles (LI) (53%) (Table 2)
Summary
Migratory marine mega vertebrates are often long lived and utilise a variety of habitats that span wide spatio-temporal scales. Species with complex life history patterns pose challenges to the understanding of population dynamics and the connectivity between breeding and non-breeding areas (Godley et al, 2010) Due to their wide-ranging movements, marine migratory species are exposed to different threats at their foraging and breeding habitats, and are further exposed to additional pressures as they migrate between these habitats (Jensen et al, 2016; Lascelles et al, 2014). These species often pass through the waters of multiple nations or areas beyond national jurisdiction (Lascelles et al, 2014) and as a result, monitoring, managing and conserving such species is challenging (Hamann et al, 2010; Jensen et al, 2016). A sound understanding of the spatial ecology of these species is essential to developing effective conservation strategies (Cooke, 2008), as it allows for the identification of key habitats and the likely sources of threatening processes
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