# A synthetic indicator based on nesting trend to inform the general public about the status of sea turtle in France and its overseas territories

Alexandre Girard, Florian Barnier, Françoise Claro, Marc Girondot

## ► To cite this version:

Alexandre Girard, Florian Barnier, Françoise Claro, Marc Girondot. A synthetic indicator based on nesting trend to inform the general public about the status of sea turtle in France and its overseas territories. Internation Sea Turtle Symposium, Mar 2023, Cartagena (Colombia), Colombia. mnhn-04119615

HAL Id: mnhn-04119615

https://mnhn.hal.science/mnhn-04119615

Submitted on 6 Jun 2023

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# A synthetic indicator based on nesting trend to inform the general public about the status of sea turtle in France and its overseas territories

by Alexandre Girard¹*; Florian Barnier¹; Françoise Claro¹ & Marc Girondot²

1. PatriNat, National Museum of Natural History, France

2. Paris Saclay University, Gif sur Yvette, France

* corresponding author : alexandre.girard@mnhn.fr

## Context

France and its overseas territories is hosting 6 species of sea turtles : the leatherback turtle (Dermochelys coriacea), the Loggerhead turtle (Caretta caretta), the green turtle (Chelonia mydas), the Olive Ridley (Lepidochelys olivacea), and the Hawksbill turtle (Eretmochelys imbricata), the Kemp Ridley (Lepidochelys kempii). The first five are observed on nesting sites (see the Map).

## Method

Based on SWOT Minimum Standard, the Groupe Tortues Marines France (GTMF) established in 2015 a national monitoring scheme through which all the actors are implementing morning patrols to count trawls on nesting beaches. Monitoring effort is adapted by actors in the field according to SWOT recommendation based on Pr. Marc Girondot's works to optimize nesting phenology modeling.

Data are then analyzed thank to R package Phenology (function Phenology and fitRMU) to produce trends taking into account possible shift in nesting effort along time.

As nesting activity trends is a proxy of nesting female abundance, trends obtained for each species on every French territory hosting sea turtle nestings are then valorized to inform a synthetic indicator describing the overall trends of adult nesting female in France. Only the site-species were the time series of standard monitoring are covering at least 5 out of the last 7 nesting season are included.

## Results

25 species-sites are known, of which 9 are considered as primary (Table 2 and Map) i.e. representing significant contribution to the world population for the species of concern.

Out of the 25 species-sites, 9 meet the indicator requirement (data of at least 5 year during the last 7 seasons to allow for assessing a trend on 7 years) (Table 1).

Among major sites, 8 out of 9 are included. 16 species sites are not included (Table 2 and Figure 2).

For 7 out of the 9 documented sites, the trend is steady.

For one species sites, the 7 year trends is decreasing (Leatherback in French Guiana). And an increasing trend is observed for Green turtle in Tromelin (Eparses Island in the Mozambican channel). The synthetic indicator is therefore presented as follows

« On 11% of the nesting sites frequented by sea turtles and documented, nesting activities have decreased over the last 7 years. On 78% of sites, the trend is not different from a stable state (7 out of 9 sites) On 11% of sites (1 site out of 9) the trend is increasing » (Figures 1A & 1B).

## Discussion - perspectives

This synthetic indicator gives an insight of the global situation of the reproductive female population in France where 5 species are observed nesting in territories dispersed all over the world in 3 Oceans.

It is meant to communicate toward general public in the official French website: https://naturefrance.fr/

The sea turtle synthetic indicators will be a doorway to detail further specific situation according to species and territories.

Next improvement steps will include: i) To acquire traditional knowledge and historical sources to put recent nesting activities and trends in perspective with historical levels; ii) To document additional species x sites pairs and primary the last major nesting site not included in the indicator at this stage: Loggerheads in New-Caledonia; iii) To include new emerging nesting sites: Wallis et Futuna and French mediterranean coast.

<figure><img src="image_2.png" /><figcaption>Figures 1A & 1B. Evolution trends of sea turtle nesting activities by site over the last seven years. A. Only documented sites B. All sites</figcaption></figure>

<figure><img src="image_3.png" /><figcaption>Table 1. Evolution of nesting sea turtle population Proportion of sites frequented by sea turtles and recently documented, on which nesting activities have decreased over the last 7 years</figcaption></figure>

<table><thead><tr><th>Site</th><th>Territory</th><th>Species</th><th>Mean annual number of nesting activities</th><th>7 year-trend</th></tr></thead><tbody><tr><td>Entrecasteau</td><td>New-Caledonia</td><td>Green</td><td>39 181</td><td>No detectable adverse evolution</td></tr><tr><td>Chesterfield et Bellona</td><td>New-Caledonia</td><td>Green</td><td>28 364</td><td>No detectable adverse evolution</td></tr><tr><td>Europa</td><td>Eparses islands</td><td>Green</td><td>14 453</td><td>No detectable adverse evolution</td></tr><tr><td>Moya-Saziley</td><td>Mayotte</td><td>Green</td><td>11 035</td><td>No detectable adverse evolution</td></tr><tr><td>Tromelin</td><td>Eparses islands</td><td>Green</td><td>9 898</td><td><strong>Increasing</strong></td></tr><tr><td>Guadeloupe et Saint Martin</td><td>Guadeloupe & Saint Martin</td><td>Hawksbill</td><td>5 916</td><td>No detectable adverse evolution</td></tr><tr><td>Guadeloupe et Saint Martin</td><td>Guadeloupe & Saint Martin</td><td>Green</td><td>3 050</td><td>No detectable adverse evolution</td></tr><tr><td>Yalimapo Guyane</td><td>French Guiana</td><td>Leatherback</td><td>2 732</td><td><strong>Decreasing</strong></td></tr><tr><td>Guadeloupe et Saint Martin</td><td>Guadeloupe & Saint Martin</td><td>Leatherback</td><td>495</td><td>No detectable adverse evolution</td></tr><tr><td></td><td></td><td>Nombre de sites les plus fréquentés</td><td></td><td>9</td></tr><tr><td></td><td></td><td>Number of species x sites on which nesting activities have decreased</td><td></td><td>1</td></tr><tr><td></td><td></td><td>Proportion of sites with declining nesting activities</td><td></td><td>11%</td></tr></tbody></table>

Note: To be integrated, a site must have been tracked for 5 years in the last 7 years. The 7-year trends represent short-term trends for sea turtles. Source: Groupe Tortues Marines France (GTMF) / PatriNat (OFB-MNHN), Paris France.

<table><caption>Table 2. List and details of pairs species x site in France and its overseas territories</caption><thead><tr><th>Species</th><th>Scientific name</th><th>Territory</th><th>Site</th><th>Primary (of international importance) or secondary site for the species</th><th>Mean number of nesting activities on 7 year</th><th>Time serie's trend</th></tr></thead><tbody><tr><td>Green</td><td>Chelonia mydas</td><td>New-Caledonia</td><td>Entrecasteau</td><td>Primary</td><td>39 181</td><td>No detectable adverse evolution</td></tr><tr><td>Green</td><td>Chelonia mydas</td><td>New-Caledonia</td><td>Entrecasteau</td><td>Primary</td><td>28 364</td><td>No detectable adverse evolution</td></tr><tr><td>Green</td><td>Chelonia mydas</td><td>Eparses islands (Mozambic channel)</td><td>Europa</td><td>Primary</td><td>14 453</td><td>No detectable adverse evolution</td></tr><tr><td>Green</td><td>Chelonia mydas</td><td>Mayotte</td><td>Moya-Saziley</td><td>Primary</td><td>11 035</td><td>No detectable adverse evolution</td></tr><tr><td>Green</td><td>Chelonia mydas</td><td>Eparses islands (Mozambic channel)</td><td>Guadeloupe et Saint Martin</td><td>secondary/Primary</td><td>9 898</td><td>Increasing</td></tr><tr><td>Hawksbill</td><td>Eretmochelys imbricata</td><td>Guadeloupe & Saint Martin</td><td>Guadeloupe et Saint Martin</td><td>secondary</td><td>5 916</td><td>No detectable adverse evolution</td></tr><tr><td>Green</td><td>Chelonia mydas</td><td>Guadeloupe & Saint Martin</td><td>Guadeloupe et Saint Martin</td><td>secondary</td><td>3 050</td><td>No detectable adverse evolution</td></tr><tr><td>Leatherback</td><td>Dermochelys coriacea</td><td>French Guyana</td><td>Yalimapo Guyane</td><td>Primary</td><td>2 732</td><td>Decreasing</td></tr><tr><td>Leatherback</td><td>Dermochelys coriacea</td><td>French Guyana</td><td>Guadeloupe et Saint Martin</td><td>secondary</td><td>495</td><td>No detectable adverse evolution</td></tr><tr><td>Hawksbill</td><td>Eretmochelys imbricata</td><td>Mayotte</td><td>Mayotte</td><td>secondary</td><td>Monitored, trend not assessed yet</td><td>Not documented</td></tr><tr><td>Hawksbill</td><td>Eretmochelys imbricata</td><td>Eparses islands (Mozambic channel)</td><td>Tromelin</td><td>secondary</td><td>Monitored, trend not assessed yet</td><td>Not documented</td></tr><tr><td>Hawksbill</td><td>Eretmochelys imbricata</td><td>Eparses islands (Mozambic channel)</td><td>Europa</td><td>secondary</td><td>Monitored, trend not assessed yet</td><td>Not documented</td></tr><tr><td>Green</td><td>Chelonia mydas</td><td>Eparses islands (Mozambic channel)</td><td>Glorieuse</td><td>Primary</td><td>Monitored, trend not assessed yet</td><td>Not documented</td></tr><tr><td>Hawksbill</td><td>Eretmochelys imbricata</td><td>Eparses islands (Mozambic channel)</td><td>Glorieuse</td><td>secondary</td><td>Monitored, trend not assessed yet</td><td>Not documented</td></tr><tr><td>Green</td><td>Chelonia mydas</td><td>Saint Barthélemy</td><td>Saint Barthélemy</td><td>secondary</td><td>Monitored, trend not assessed yet</td><td>Not documented</td></tr><tr><td>Hawksbill</td><td>Eretmochelys imbricata</td><td>Saint Barthélemy</td><td>Saint Barthélemy</td><td>secondary</td><td>Monitored, trend not assessed yet</td><td>Not documented</td></tr><tr><td>Leatherback</td><td>Dermochelys coriacea</td><td>Saint Barthélemy</td><td>Saint Barthélemy</td><td>secondary</td><td>Monitored, trend not assessed yet</td><td>Not documented</td></tr><tr><td>Green</td><td>Chelonia mydas</td><td>Martinique</td><td>Martinique</td><td>secondary</td><td>Monitored, trend not assessed yet</td><td>Not documented</td></tr><tr><td>Leatherback</td><td>Dermochelys coriacea</td><td>Martinique</td><td>Martinique</td><td>secondary</td><td>Monitored, trend not assessed yet</td><td>Not documented</td></tr><tr><td>Olive Ridley</td><td>Lepidochelys olivacea</td><td>French Guiana</td><td>Guyane</td><td>Primary</td><td>Monitored, trend not assessed yet</td><td>Not documented</td></tr><tr><td>Green</td><td>Chelonia mydas</td><td>Caretta caretta</td><td>Roche percée</td><td>Primary</td><td>Monitored, trend not assessed yet</td><td>Not documented</td></tr><tr><td>Loggerhead</td><td>Caretta caretta</td><td>Chelonia mydas</td><td>Grand Lagon sud</td><td>secondary</td><td>Monitored, trend not assessed yet</td><td>Not documented</td></tr><tr><td>Green</td><td>Chelonia mydas</td><td>Chelonia mydas</td><td>Tetiaora</td><td>secondary</td><td>Monitored, trend not assessed yet</td><td>Not documented</td></tr><tr><td>Green</td><td>Chelonia mydas</td><td>Caretta caretta</td><td>Continental France and Corsica</td><td>secondary</td><td>Emerging nesting site</td><td>From erratic to regular nesting (Emerging nesting site)</td></tr></tbody></table>

Note: Pour être intégré, un site doit avoir été suivi 5 années au cours des 7 dernière années. Les tendances à 7 ans représentent des tendances à court terme pour les tortues marines. Source: Groupe Tortues Marines France (GTMF) / PatriNat (OFB-MNHN)

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