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Low growth rates at high population densities in sea turtles

Jeanne A. Mortimer, Nicole Esteban Orcid Logo, Jacques-Olivier Laloë, Holly Stokes Orcid Logo, Jared J. Tromp, Graeme C. Hays

Marine Biology, Volume: 172, Issue: 6

Swansea University Authors: Nicole Esteban Orcid Logo, Holly Stokes Orcid Logo

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DOI (Published version): 10.1007/s00227-025-04638-z

Abstract

Over 29 years (1996–2024) in a lagoon environment in the Chagos Archipelago (Indian Ocean) we conducted a mark-recapture growth rate study during which 135 juvenile hawksbill turtles (Eretmochelys imbricata) were each caught two or more times. Growth rate in straight carapace length (SCL) decreased...

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Published in: Marine Biology
ISSN: 0025-3162 1432-1793
Published: Springer Science and Business Media LLC 2025
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URI: https://cronfa.swan.ac.uk/Record/cronfa69286
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Growth rate in straight carapace length (SCL) decreased in larger turtles with predicted mean growth rate for turtles with a starting SCL of 35 cm at 1.64 cm.y&#x2212;1, decreasing to 0.90 cm.y&#x2212;1 for a SCL of 60 cm: SCL(cm.y&#x2212;1) = -0.03 x SCL&#x2009;+&#x2009;2.68 (R2&#x2009;=&#x2009;0.15; F1,162 = 28.24, p&#x2009;&lt;&#x2009;0.001). After 2006, the size structure of the population changed, most likely because of an influx of small turtles (30&#x2013;40 cm SCL). The resulting increase in population density may explain the decrease in size specific growth rates and body condition (calculated as mass/(SCL2 x SCW)) over time, with growth rates being faster at the start of the time series and slower at the end. 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spelling 2025-05-22T16:28:20.0897011 v2 69286 2025-04-14 Low growth rates at high population densities in sea turtles fb2e760b83b4580e7445092982f1f319 0000-0003-4693-7221 Nicole Esteban Nicole Esteban true false 6ee6932996059ed9e4d581641acce2f7 0000-0001-9401-913X Holly Stokes Holly Stokes true false 2025-04-14 BGPS Over 29 years (1996–2024) in a lagoon environment in the Chagos Archipelago (Indian Ocean) we conducted a mark-recapture growth rate study during which 135 juvenile hawksbill turtles (Eretmochelys imbricata) were each caught two or more times. Growth rate in straight carapace length (SCL) decreased in larger turtles with predicted mean growth rate for turtles with a starting SCL of 35 cm at 1.64 cm.y−1, decreasing to 0.90 cm.y−1 for a SCL of 60 cm: SCL(cm.y−1) = -0.03 x SCL + 2.68 (R2 = 0.15; F1,162 = 28.24, p < 0.001). After 2006, the size structure of the population changed, most likely because of an influx of small turtles (30–40 cm SCL). The resulting increase in population density may explain the decrease in size specific growth rates and body condition (calculated as mass/(SCL2 x SCW)) over time, with growth rates being faster at the start of the time series and slower at the end. For turtles in the SCL size classes 40–50 and 50–60 cm, when the initial measurement was taken prior to 1999 versus after 2018, the mean growth rates (SCL) decreased from 1.92 to 1.36 cm.y−1 and from 1.43 to 0.67 cm.y−1 in these two size classes respectively. A survey of 35 studies of hawksbill growth rates around the world showed that the size specific growth rates we recorded for immature hawksbills in the Chagos Archipelago are the lowest ever found for this species, likely due to density-dependent growth rates limited by food supply. Our findings point to the low growth rates that might have occurred more broadly prior to human exploitation of hawksbill turtles. Journal Article Marine Biology 172 6 Springer Science and Business Media LLC 0025-3162 1432-1793 Critically endangered; Developmental habitats; Predation risk; Emigration; Carapace measurements; Global review growth rates 28 4 2025 2025-04-28 10.1007/s00227-025-04638-z COLLEGE NANME Biosciences Geography and Physics School COLLEGE CODE BGPS Swansea University SU Library paid the OA fee (TA Institutional Deal) Fondation Bertarelli (2017-4, 820633); Darwin Initiative (EIDCF008); U.S. Fish and Wildlife Service (982210-6-G073) 2025-05-22T16:28:20.0897011 2025-04-14T10:33:23.6753686 Faculty of Science and Engineering School of Biosciences, Geography and Physics - Biosciences Jeanne A. Mortimer 1 Nicole Esteban 0000-0003-4693-7221 2 Jacques-Olivier Laloë 3 Holly Stokes 0000-0001-9401-913X 4 Jared J. Tromp 5 Graeme C. Hays 6 69286__34337__596ac2f9a3aa4f34bab22657d49c3363.pdf 69286.VoR.pdf 2025-05-22T16:25:35.8429070 Output 1683737 application/pdf Version of Record true © The Author(s) 2025. This article is licensed under a Creative Commons Attribution 4.0 International License. true eng http://creativecommons.org/licenses/by/4.0/
title Low growth rates at high population densities in sea turtles
spellingShingle Low growth rates at high population densities in sea turtles
Nicole Esteban
Holly Stokes
title_short Low growth rates at high population densities in sea turtles
title_full Low growth rates at high population densities in sea turtles
title_fullStr Low growth rates at high population densities in sea turtles
title_full_unstemmed Low growth rates at high population densities in sea turtles
title_sort Low growth rates at high population densities in sea turtles
author_id_str_mv fb2e760b83b4580e7445092982f1f319
6ee6932996059ed9e4d581641acce2f7
author_id_fullname_str_mv fb2e760b83b4580e7445092982f1f319_***_Nicole Esteban
6ee6932996059ed9e4d581641acce2f7_***_Holly Stokes
author Nicole Esteban
Holly Stokes
author2 Jeanne A. Mortimer
Nicole Esteban
Jacques-Olivier Laloë
Holly Stokes
Jared J. Tromp
Graeme C. Hays
format Journal article
container_title Marine Biology
container_volume 172
container_issue 6
publishDate 2025
institution Swansea University
issn 0025-3162
1432-1793
doi_str_mv 10.1007/s00227-025-04638-z
publisher Springer Science and Business Media LLC
college_str Faculty of Science and Engineering
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hierarchy_top_id facultyofscienceandengineering
hierarchy_top_title Faculty of Science and Engineering
hierarchy_parent_id facultyofscienceandengineering
hierarchy_parent_title Faculty of Science and Engineering
department_str School of Biosciences, Geography and Physics - Biosciences{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Biosciences, Geography and Physics - Biosciences
document_store_str 1
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description Over 29 years (1996–2024) in a lagoon environment in the Chagos Archipelago (Indian Ocean) we conducted a mark-recapture growth rate study during which 135 juvenile hawksbill turtles (Eretmochelys imbricata) were each caught two or more times. Growth rate in straight carapace length (SCL) decreased in larger turtles with predicted mean growth rate for turtles with a starting SCL of 35 cm at 1.64 cm.y−1, decreasing to 0.90 cm.y−1 for a SCL of 60 cm: SCL(cm.y−1) = -0.03 x SCL + 2.68 (R2 = 0.15; F1,162 = 28.24, p < 0.001). After 2006, the size structure of the population changed, most likely because of an influx of small turtles (30–40 cm SCL). The resulting increase in population density may explain the decrease in size specific growth rates and body condition (calculated as mass/(SCL2 x SCW)) over time, with growth rates being faster at the start of the time series and slower at the end. For turtles in the SCL size classes 40–50 and 50–60 cm, when the initial measurement was taken prior to 1999 versus after 2018, the mean growth rates (SCL) decreased from 1.92 to 1.36 cm.y−1 and from 1.43 to 0.67 cm.y−1 in these two size classes respectively. A survey of 35 studies of hawksbill growth rates around the world showed that the size specific growth rates we recorded for immature hawksbills in the Chagos Archipelago are the lowest ever found for this species, likely due to density-dependent growth rates limited by food supply. Our findings point to the low growth rates that might have occurred more broadly prior to human exploitation of hawksbill turtles.
published_date 2025-04-28T05:29:08Z
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score 11.096068

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