Synergistic use of UAV surveys, satellite tracking data, and mark‐recapture to estimate abundance of elusive species

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.

Using water‐landing, fixed‐wing UAVs and computer vision to assess seabird nutrient subsidy effects on sharks and rays

“…Flights at Turtle Cove on Diego Garcia were excluded from this analysis because they were targeted at a known immature turtle aggregation (Stokes et al., 2023) area and could not therefore be expected to give a representative picture of turtle distribution in the area. Exploratory analysis of the remaining data revealed that turtle and teleost detections were too spatially aggregated to support robust statistical inference, however, elasmobranch observations were sufficiently dispersed.…”

Applications, Evolutions, and Challenges of Drones in Maritime Transport

“…Additionally, drones can access and survey challenging marine areas that are typically inaccessible or hazardous for humans [96,97]. This enables data collection from remote or neglected locations, providing a comprehensive understanding of species populations, habitat conditions, and environmental changes.…”

Long‐term (29‐year) spatiotemporal patterns of sea turtle deaths in the southern Gulf of Mexico

“…On the other hand, mortality records of reproductive females at nesting beaches also inform about in‐land threats that frequently cause the deaths of individuals in the breeding population. Available technology has made it feasible to expand this on‐site knowledge using tools such as satellite telemetry, vessel‐based surveys, bycatch quantification and drone imagery to maximize the information regarding the injury or death causes for those stranded or rescued individuals (Raoult et al, 2020; Schofield et al, 2019; Stokes et al, 2022). The combination of several of these data sources proved to be effective when integrated with ocean circulation models to evaluate the spatial distribution of male sea turtles (Cuevas et al, 2020; Nero et al, 2013) and the distribution of offspring during the ‘lost years’, which typically occur in oceanic zones (Putman et al, 2019).…”