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Synergistic use of UAV surveys, satellite tracking data, and mark-recapture to estimate abundance of elusive species
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Nicole Esteban
Ecosphere, Volume: 14, Issue: 3
Swansea University Authors:
Holly Stokes, Nicole Esteban
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DOI (Published version): 10.1002/ecs2.4444
Abstract
Estimating population abundance is central to many ecological studies and important in conservation planning. Yet the elusive nature of many species makes estimating their abundance challenging. Abundance estimates of sea turtles, marine birds, and seals are usually made when breeding adults are ash...
| Published in: | Ecosphere |
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| ISSN: | 2150-8925 2150-8925 |
| Published: |
Wiley
2023
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| Online Access: |
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| URI: | https://cronfa.swan.ac.uk/Record/cronfa62644 |
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| Abstract: |
Estimating population abundance is central to many ecological studies and important in conservation planning. Yet the elusive nature of many species makes estimating their abundance challenging. Abundance estimates of sea turtles, marine birds, and seals are usually made when breeding adults are ashore, while life stages spent at sea, including as juveniles, are often poorly sampled. We used a combination of high-resolution satellite tracking (Fastloc-GPS), uncrewed aerial vehicle (UAV) surveys, and capture-mark-recapture approaches to assess the abundance of immature hawksbill (Eretmochelys imbricata) and green turtles (Chelonia mydas) in a tidal lagoon of the Chagos Archipelago (Indian Ocean). We captured, marked, and released 50 turtles (48 hawksbill and 2 green turtles) prior to UAV surveys and used satellite tracking data from 27 immature turtles (25 hawksbill and 2 green turtles) to refine the estimated numbers of marked turtles available for resighting and those likely to have emigrated from the study area. We estimated a total of 339 turtles in the lagoon with a density variation at different tidal heights between 265 turtles km−2 at high water and 499 turtles km−2 at low water. Of these, 91% were hawksbills and 9% were green turtles. These hawksbill densities are the highest reported among 17 foraging sites recorded around the world and likely reflect successful long-term protection of turtles in the Chagos Archipelago. |
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| Keywords: |
Conservation, density, drone, endangered species, marine megafauna, marine protected area (MPA), mark-resight, satellite tracking, shifting baseline |
| College: |
Faculty of Science and Engineering |
| Funders: |
This work was supported by the Bertarelli Foundation as part of the Bertarelli Programme in Marine Science (BPMS-2017-4 and 820633). All work was approved by the Swansea University and Deakin University Ethics Committees and the British Indian Ocean Territory (BIOT) Administration of the UK Foreign, Commonwealth, and Development Office. The study was endorsed through research permits (0006SE18, 0009SE18, 0004SE19, and 0001SE21) from the Commissioner's Representative for BIOT, and the research complied with all relevant local and national legislation. We thank the many volunteers on Diego Garcia for logistical and fieldwork support. |
| Issue: |
3 |