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ESR 41:141-151 (2020)  -  DOI: https://doi.org/10.3354/esr01019

Sea turtle populations are overestimated worldwide from remigration intervals: correction for bias

Paolo Casale1,*, Simona A. Ceriani2,3

1Department of Biology, University of Pisa, Via A. Volta 6, 56126 Pisa, Italy
2Fish and Wildlife Research Institute, Florida Fish and Wildlife Conservation Commission, Saint Petersburg, FL, USA
3Department of Biology, University of Central Florida, Orlando, FL, USA
*Corresponding author:

ABSTRACT: Estimating population abundance is key for species of conservation concern. This is particularly challenging for marine animals, like sea turtles, with ocean-scale distribution and migratory nature. However, sea turtles lay clutches on land where they can be easily counted; thus, clutch number has always been the most common index of population abundance. A female typically lays >1 clutch per year and does not reproduce every year. Therefore, 2 conversion factors are needed to convert the number of egg clutches to the number of adult females: the number of clutches laid by a female in a nesting season and the fraction of adult females reproducing in a season, which is linked to the breeding periodicity. The effects of breeding periodicity, probability of detection and annual survival probability on the derived adult female abundance were investigated by simulating a virtual population of adult females over a 15 yr beach monitoring period. The results indicate that current methods may greatly overestimate the abundance of sea turtle populations, especially in situations with a low detection probability, including temporary emigration. The factors involved and ways to minimize biases and errors are discussed, including a method which is easy to implement using existing datasets. A careful reassessment of current estimates of sea turtle abundance derived from nest counts and capture-mark-recapture data would be appropriate, and the potential error associated with such estimates should be considered when they are used in conservation status assessments.


KEY WORDS: Sea turtle · Remigration interval · Abundance · Breeding proportion · Mortality · Detection · Simulation


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Cite this article as: Casale P, Ceriani SA (2020) Sea turtle populations are overestimated worldwide from remigration intervals: correction for bias. Endang Species Res 41:141-151. https://doi.org/10.3354/esr01019

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