From terra incognita to hotspot: the largest South Pacific green turtle nesting population in the forgotten reefs of New Caledonia

Abstract

The green turtle Chelonia mydas is a large marine turtle present in tropical and subtropical seas of the Atlantic, Pacific and Indian Oceans. It is categorized as Endangered on the IUCN Red List based on the trend of nesting populations at 32 sites, of which only three are in the Pacific Ocean. New Caledonia is a sui generis overseas territory of France in the south-west Pacific Ocean c. 1,210 km east of Australia. The presence of green turtles in New Caledonian waters is known, although the main nesting sites are far from the main island, on remote uninhabited islands. Since 1988 field missions to these remote reefs, namely d'Entrecasteaux, Bellona and Chesterfield, have collected data to quantify the nesting of green turtles in New Caledonia. For the first time we analyse the data collected during these missions. D'Entrecasteaux, Bellona and Chesterfield Reefs host a large nesting colony of green turtles, with the upper credible estimate of nesting activities reaching 150,000 nesting tracks in some years. These numbers exceed the estimated number of green turtle activities in the Pacific. The trend of the number of nesting activities is stable and has the same relationship with the Southern Oscillation Index as observed at Australian nesting sites. Our recommendations for the French authorities are to continue monitoring these populations, collect new demographic parameters and ensure the protection of these remote reefs, which should be considered a national treasure for New Caledonia.

Innovative monitoring scheme adapted to remote, scattered nesting aggregation reveals a major loggerhead turtle rookery in New Caledonia, South Pacific

“…For each prospected islets, time series of nest counts has been fitted using the phenological parameters LengthB , LengthE and Peak of the corresponding nesting season as fixed parameters, with only the Max parameter being specific to each islet time series [ 13 , 31 ]. We obtained the posterior predictive mean number of nests during the season, then we estimated the number of nesting activities for the islets not monitored during a season.…”

“…This may lead to important knowledge gaps and significant misunderstanding of demographic processes in high-potential habitats [ 12 – 14 ]. The development of efficient and resource-optimized tools is therefore a priority as it could reveal unsuspected major nesting rookeries [ 13 ], especially in the South Pacific region that encompasses a multitude of island-rich geographies [ 15 , 16 ].…”

Assessment, planning and action for species conservation

“…Finally, in the only article in this theme covering marine environments, Fretey et al (2023) give us hope for the future of the green turtle Chelonia mydas in the Pacific. They report large nesting sites in New Caledonia, presenting the first analysis of nesting colony data from D'Entrecasteaux, Bellona and Chesterfield Reefs.…”

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“…For each prospected islets, time series of nest counts has been fitted using the phenological parameters LengthB, LengthE and Peak of the corresponding nesting season as fixed parameters, with only the Max parameter being specific to each islet time series [13,31]. We obtained the posterior predictive mean number of nests during the season, then we estimated the number of nesting activities for the islets not monitored during a season.…”

“…The high financial costs associated with field presence act indeed as a strong hindrance to the collection of core data. This may lead to important knowledge gaps and significant misunderstanding of demographic processes in high-potential habitats [12][13][14]. The development of efficient and resource-optimized tools is therefore a priority as it could reveal unsuspected major nesting rookeries [13], especially in the South Pacific region that encompasses a multitude of island-rich geographies [15,16].…”