Combining spawn egg counts, individual photo-ID and genetic fingerprinting to estimate the population size and sex ratio of an endangered amphibian

Marina Reyne*, Sarah Helyar, Aurélie Aubry, Mark Emmerson, Ferdia Marnell, Neil Reid

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)
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According to the International Union for Conservation of Nature Red List, 41% of the world's amphibian species are threatened with extinction, making them more threatened than any other vertebrate group nowadays. Given the global amphibian crisis, comprehensive understanding of demographics and population trends of declining and threatened species is essential for effective management and conservation strategies. Counting egg spawns is widely used to assess population abundance in pond breeding anurans. However, it is unknown how such counts translate into robust population size estimations. We monitored the breeding activity of the Natterjack toad (Epidalea calamita), combining egg string counts and individual photo-identification with Capture-Mark-Recapture population size and operational sex ratio estimation. Male Natterjack toads were identified by the pattern of natural markings with repeated ID of the same individual confirmed for 10% of the samples using genetic fingerprinting. We identified 647 unique individuals within a closed study population at Caherdaniel, Co Kerry. Population estimates derived from egg string counts estimated a breeding population of 368 females (95% CI 353–384) and Capture-Mark-Recapture estimated a breeding population of 1698 males (95% CI 1000–2397). The female:male sex ratio was conservatively estimated at 1:5 (95% CI 1:3–1:6) where 62% ± 6% of females were assumed to spawn. These substantially departed from any priori assumption of 1:1 which could have underestimated the breeding population by up to 72%. Where amphibian absolute population size estimation is necessary, methods should include empirical survey data on operational sex ratios and not rely on assumptions or those derived from the literature which may be highly population and/or context-dependent.

Original languageEnglish
JournalIntegrative zoology
Early online date04 Dec 2020
Publication statusEarly online date - 04 Dec 2020

Bibliographical note

Funding Information:
This study was part of a larger monitoring and surveillance project commissioned and funded by the National Parks and Wildlife Service (NPWS), Department of Culture, Heritage and the Gaeltacht (CHG), Republic of Ireland. Natterjack toads were collected under Government license (No. C098/2016). We are grateful to all field assistants and work placement students from Queen's University Belfast (QUB) and Institute of Technology Tralee (ITT) who participated in data collection and we thank the landowners and farmers who provided access to their land.

Publisher Copyright:
© 2020 International Society of Zoological Sciences, Institute of Zoology/Chinese Academy of Sciences and John Wiley & Sons Australia, Ltd.

Copyright 2020 Elsevier B.V., All rights reserved.


  • Epidalea calamita
  • genetic fingerprinting
  • Mark-Recapture
  • Natterjack toad
  • photo-identification

ASJC Scopus subject areas

  • Animal Science and Zoology


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