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Bias in sea turtle productivity estimates: error and factors involved

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Abstract

The conservation and management of endangered species, including sea turtles, require consistent long-term monitoring of productivity (e.g., number of hatchlings emerged per nest, per female, per nesting site, per population). In sea turtle species, some of the relevant data are obtained by estimating the number of hatched eggs from fragments found in the nest after hatching. Yet, no formal assessment of the associated error has been published. Here we provide an estimation of the error associated with the most widespread method used to determine sea turtle productivity (count of shell fragments > 50% of the egg size) using a large dataset (n = 8539) of actual and estimated clutch sizes of four sea turtle species (Caretta caretta, Chelonia mydas, Dermochelys coriacea, Eretmochelys imbricata). The data are analyzed through linear mixed models with several explanatory variables. Results show that the error can be large in certain cases and, when the associated error rate is not adequately considered, may represent a serious problem in studies on reproductive parameters such as clutch size. Some significant explanatory variables suggest that some sources of error are linked to species-specific biological traits (e.g., clutch size, egg size, nest depth), and others imply human error. Other biotic and abiotic factors may also be involved. We recommend that—whenever possible—errors be assessed and adequately reported by studies that estimate clutch size, hatching and emergence success, or hatchling production.

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Data availability

The dataset analysed during the current study will be provided upon reasonable request submitted to the corresponding author.

Code availability

The code to assist in data analysis will be provided upon reasonable request submitted to the corresponding author.

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Acknowledgments

We thank the coordinated network of Florida sea turtle permit holders, who collected the Florida data analyzed here, for their dedication and effort on behalf of sea turtle conservation. In Panama, thanks are due to many local community members, especially Inocencio Castillo, Arcelio González Hooker, and Luis Baker, who have worked many years on the project. We thank Cristina Ordoñez (Sea Turtle Conservancy) for logistic support and help with data management, and the Smithsonian Tropical Research Institute for assistance of many kinds. We thank J. Miller, C. Limpus, L. Ehrhart and J. Mortimer for providing historical context regarding the method used to conduct nest evaluation. We also thank M. Koperski and S. Pessolano for their insight into D. coriacea nest excavations. We thank A. Foley, L. Soares, B. Crowder and two anonymous reviewers for their constructive suggestions to improve the manuscript.

Funding

Funding for the Florida sea turtle nest counts program has come from the U.S. Fish and Wildlife Service and from the Marine Resources Conservation Trust Fund (thanks to the Florida Sea Turtle License Plate program, https://helpingseaturtles.org/get-a-plate/). Funding for the work in the Zapatilla Cays has come primarily from a series of grants to A. and P. Meylan from the Marisla Foundation.

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Authors and Affiliations

  1. Fish and Wildlife Research Institute, Florida Fish and Wildlife Conservation Commission, 100 8th Avenue SE, St. Petersburg, FL, 33701, USA

    Simona A. Ceriani, Beth Brost & Anne B. Meylan

  2. Smithsonian Tropical Research Institute, Balboa, Panama

    Anne B. Meylan & Peter A. Meylan

  3. Natural Sciences Collegium, Eckerd College, 4200 54th Avenue South, St. Petersburg, FL, 33711, USA

    Peter A. Meylan

  4. Department of Biology, University of Pisa, Via A. Volta 6, 56126, Pisa, Italy

    Paolo Casale

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  1. Simona A. Ceriani
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  2. Beth Brost
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  3. Anne B. Meylan
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  4. Peter A. Meylan
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Contributions

SAC conceived the study. BB collated the dataset for Florida. PC conducted the statistical analysis. ABM and PAM contributed the dataset from Panama. SAC and PC led the writing of the manuscript with contributions from ABM and PAM.

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Correspondence to Simona A. Ceriani.

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The authors declare that they have no conflict of interest.

Ethical approval

All applicable international, national and institutional guidelines for handling sea turtle eggs have been followed and all necessary approvals have been obtained. The research conducted for this project was undertaken with the authority and under the supervision of SA Ceriani and AB Meylan as Sea Turtle Nesting Program Coordinators for the Florida Fish and Wildlife Conservation Commission, the institution responsible for regulating sea turtle monitoring and conservation and issuing permits in Florida. Research activity and data collection in Panama were authorized under a series of permits from Autoridad Nacional del Ambiente and Ministerio de Ambiente, the most recent (2016) being SE/A-54–16.

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Consent for participation is not applicable to this study as there were no human test subjects.

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Ceriani, S.A., Brost, B., Meylan, A.B. et al. Bias in sea turtle productivity estimates: error and factors involved. Mar Biol 168, 41 (2021). https://doi.org/10.1007/s00227-021-03843-w

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