Green and hawksbill sea turtle nesting in the Gulf of Guinea: A 9-year survey
Data files
Mar 15, 2024 version files 1.15 MB
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ProgramaTato_NestingData_20122023.xlsx
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README.md
Apr 26, 2024 version files 896.16 KB
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ProgramaTato_NestingData_20122023.xlsx
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README.md
Abstract
Sea turtles are critical components of marine ecosystems, and their conservation is important for Ocean Governance and Global Planet Health. However, there is limited knowledge of their ecology in the Gulf of Guinea. To fill this knowledge gap, this study presents the first integrative assessment of green and hawksbill turtles in the region, combining nesting area surveys over 9 years, and telemetry data, to offer insights into these population dynamics, and behaviours including nesting preferences, morphological and reproductive parameters, diving patterns and inter-nesting core-use areas. Green turtles are likely making a recovery in São Tomé, potentially driven by sustained conservation efforts. In contrast, the status of the hawksbill turtle remains less clear. There are preliminary indications of recovery, but we interpret this cautiously. Coupled with satellite tracking, this study estimated that 482 to 736 green turtles, and 135 to 217 hawksbills, nest on the beaches of São Tomé. Their movements overlap significantly with a proposed Marine Protected Area (MPA), which suggests they may be well placed for conservation if managed appropriately. However, the presence of artisanal fisheries and emerging threats, such as sand mining and unregulated tourism, highlight the urgent need for robust management strategies that align global conservation objectives with local socioeconomic realities. This study significantly enhances our understanding of the ecology and conservation needs of the green and hawksbill turtles in the Gulf of Guinea. The insights gleaned here can contribute to the development of tailored conservation strategies that benefit these populations and the ecosystem services upon which they depend.
README: Green and hawksbill sea turtle nesting in the Gulf of Guinea: A 9-year survey
The dataset is structured with the following variables:
- RecCode: This is a unique automated code generated to link related datasets across multiple databases for tracking and analysis purposes.
- Season: Indicates the nesting season, spanning from July of one year to May of the following year, to accommodate the annual nesting cycle of the species.
- NewDate: Indicates the date of the nesting or false crawl event.
- Area: Indicates the area where the event occurred. Not the specific nesting beach but the area.
- Specie: Specifies the species of the turtle. CM stands for Chelonia mydas (Green Turtle) and EI stands for Eretmochelys imbricata (Hawksbill Turtle).
- LeftTag and RighhTag: Each turtle has one or two tags, in the left or right flippers.
- NewRecap: Designates whether the turtle is a new individual to the study (1 for New Turtle) or a recaptured individual that has been previously tagged or identified (2 for Recapture Turtle).
- CCL: Curved Carapace Length measured in centimeters (cm), from the nuchal notch to the tip of the supracaudal scute.
- CCW: Curved Carapace Width measured in centimeters (cm), across the carapace at its widest point.
- Nest: Binary indicator of nesting activity, where 1 denotes a successful nesting event (Nest) and 0 denotes an unsuccessful attempt or false crawl.
- Type of Nest: Categorizes the nest based on its condition or management as follows - 1 for nests left in situ, 2 for nests transferred to a different location on the beach, and 3 for nests moved to a hatchery.
- NestDepth and NestWidth: Transferred nests to a different location on the beachor to a hatchery were record the depth (cm) and width (cm).
- Shells: Counts the total number of eggshells found within a nest, indicating the number of eggs that were laid.
- Dead Hatch: The count of dead hatchlings discovered inside the nest post-emergence.
- Total Eggs: The total count of eggs laid in a single nesting event.
- Live Hatch: The number of live hatchlings that emerged from the nest.
- EmergeRate: The hatchling emergence rate, is calculated as the proportion of live hatchlings to the total number of eggs.
- EmergeDate: The date on which hatchlings emerged from the nest.
- IncubPer: The incubation period, recorded as the number of days between the laying of eggs and the emergence of hatchlings.
Empty cells in our dataset indicate 'null' or 'n/a,' for unavailable or inapplicable information.
If you have any questions regarding this dataset or require additional information, please contact the corresponding authors.
Methods
Nesting Data Collection and Analysis: We recorded nest parameters, whenever possible, including clutch size, nest depth, and emergence success. Females were tagged during nesting with Inconel tags (Style 681, National Band and Tag Company) in both front flippers and their curved carapace length (CCL) was measured. To analyse changes in length between nesting seasons, we used a Kruskal-Wallis test. For the CCL analyses, we considered only the first recorded data from each female per season to avoid potential bias introduced by repeat records of high-frequency nesters, ensuring that each turtle contributed only once to the data set within a nesting season. For other reproductive parameters such as clutch size, nest depth, emergence success, and incubation period, we conducted a descriptive statistical analysis using all available data from each female throughout the season. This involved calculating the mean, minimum, maximum, and standard deviation for each parameter to provide a comprehensive understanding of their distribution and variability across the nesting season. We calculated emergence success as the proportion of eggs that produced live hatchlings that reached the surface of the sand and included the failed nests (with 0% emergence success). The incubation period was determined as the number of days between the day of oviposition and the emergence of the first hatchling.