Estimates of marine turtle nesting populations in the south-west Indian Ocean indicate the importance of the Chagos Archipelago

Global marine turtle population assessments highlight the importance of the south-west Indian Ocean region, despite data gaps for the Chagos Archipelago. The archipelago hosts nesting hawksbill Eretmochelys imbricata and green turtles Chelonia mydas, both heavily exploited for 2 centuries until prot...

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Published in:Oryx Vol. 54; no. 3; pp. 332 - 343
Main Authors: Mortimer, Jeanne A., Esteban, Nicole, Guzman, Antenor Nestor, Hays, Graeme C.
Format: Journal Article
Language:English
Published: Cambridge Cambridge University Press 01.05.2020
Subjects:
Aquatic reptiles
Archipelagoes
Atolls
Caretta caretta
Chelonia mydas
Coasts
Endangered & extinct species
Eretmochelys imbricata
Estimates
Habitats
Nesting
Nesting behavior
Polls & surveys
Population
Population statistics
Seasonal variations
Spatial distribution
Trends
Turtles
British Indian Ocean Territory
Chagos Archipelago
Indian Ocean
Diego Garcia
Seychelles
ISSN:0030-6053, 1365-3008
Online Access:Get full text
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Summary:Global marine turtle population assessments highlight the importance of the south-west Indian Ocean region, despite data gaps for the Chagos Archipelago. The archipelago hosts nesting hawksbill Eretmochelys imbricata and green turtles Chelonia mydas, both heavily exploited for 2 centuries until protection in 1968–1970. We assessed available nesting habitat and spatial distribution of nesting activity during rapid surveys of 90% of the archipelago's coastline in 1996, 1999, 2006 and 2016. We quantified seasonality and mean annual egg clutch production from monthly track counts during 2006–2018 along a 2.8 km index beach on Diego Garcia island. An estimated 56% (132 km) of coastline provided suitable nesting habitat. Diego Garcia and Peros Banhos atolls accounted for 90.4% of hawksbill and 70.4% of green turtle nesting. Hawksbill turtles showed distinct nesting peaks during October–February, and green turtles nested year-round with elevated activity during June–October. Estimates of 6,300 hawksbill and 20,500 green turtle clutches laid annually during 2011–2018 indicate that nesting on the Chagos Archipelago has increased 2–5 times for hawksbill turtles and 4–9 times for green turtles since 1996. Regional estimates indicate green turtles produce 10 times more egg clutches than hawksbill turtles, and the Chagos Archipelago accounts for 39–51% of an estimated 12,500–16,000 hawksbill and 14–20% of an estimated 104,000–143,500 green turtle clutches laid in the south-west Indian Ocean. The improved status may reflect > 40 years without significant exploitation. Long-term monitoring is needed to captureinterannual variation in nesting numbers and minimize uncertainty in population estimates.
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ISSN:0030-6053
1365-3008
DOI:10.1017/S0030605319001108