Using small drones to photo-identify Antillean manatees: a novel method for monitoring an endangered marine mammal in the Caribbean Sea

Abstract

Population assessments and species monitoring for many endangered marine megafauna are limited by the challenges of identifying and tracking individuals that live underwater in remote and sometimes inaccessible areas. Manatees can acquire scars from watercraft injury and other incidences that can be used to identify individuals. Here we describe a novel method for photo-identification of Antillean manatees Trichechus manatus manatus using aerial imagery captured during flights with a small multirotor drone. Between 2016 and 2017, we conducted 103 flights to detect and observe manatees in Belize, primarily at St. George's Caye (SGC) near the Belize Barrier Reef. Review of aerial videos from these flights resulted in 279 sightings of manatees (245 adults, 34 calves). High-resolution images of individual manatees were extracted and classified according to image quality and distinctiveness of individual manatees for photoidentification. High-quality images of manatees classified as sufficiently distinctive were used to create a catalog of 17 identifiable individuals. At SGC, 21% of all sighted adult manatees (N = 214) were considered photo-identifiable over time. We suggest that the method can be used for investigating individual site fidelity, habitat use, and behavior of manatee populations. Our photoidentification protocol has the potential to improve long-term monitoring of Antillean manatees in Belize and can be applied throughout clear, shallow waters in the Caribbean and elsewhere.

Operational Protocols for the Use of Drones in Marine Animal Research

“…Regarding imagery for photo-ID purposes, the representative features and scars can be distorted or masked due to ripples, light diffusion on water, and turbidity [117]. It is also challenging to obtain manatee images depicting the whole body in straight position and near surface, most suitable for photogrammetry purposes.…”

“…Both multirotor and fixed-wing drones can be used for the purpose of detecting sirenians (e.g., [15,117]). On the other hand, multirotor drones can maintain stationary flight, allowing the capture of high-quality images and videos of surfacing marine mammals [114], which can be useful for studies based on photogrammetry and photo-identification.…”

“…Since drones obtain overhead views, they are ideal for capturing images on the dorsum of sirenians, which is the part of the body where the most conspicuous boat-related injuries are typically found [125]. Landeo-Yauri, et al [117] proposed a protocol for manatee photo-ID using multirotor off-the shelve drones, extracting suitable images from aerial videos, selecting them according to image quality and distinctiveness of manatee features, and compiling a catalog of distinctive individuals. The most adequate images for photo-ID were obtained below 30 m flight altitude using DJI Phantom 3 and Phantom 4 drones.…”

Mating patterns of dusky dolphins (Lagenorhynchus obscurus) explored using an unmanned aerial vehicle

“…UAVs have become waterproof and more affordable, with longer battery life, larger ranges of travel, and reduced noise production (Christiansen, Rojano‐Doñate, Madsen, & Bejder, 2016; Fiori, Doshi, Martinez, Orams, & Bollars‐Breen, 2017). While applications of UAVs to cetacean research have typically centered on abundance estimates, photogrammetry, and photo‐identification (Durban et al, 2016; Fiori et al, 2017; Koski et al, 2015; Landeo‐Yauri, Ramos, Niño‐Torres, Castelblanco‐Martinez, & Searle, 2019), some recent research efforts have assessed behavioral patterns (Fiori, Martinez, Bader, Orams, & Bollard‐Breen, 2019; Nielsen, Sprogis, Bejder, Madsen, & Christiansen, 2019; Torres, Nieukirk, Lemos, & Chandlerm 2018; Weir et al, 2018). Our objective was to assess the behavioral patterns of dusky dolphins in mating groups collected from UAV footage.…”

Food sharing in rough‐toothed dolphins off southwestern Mexico

“…Our findings illustrate the power of small aerial drones to track and document the fine‐scale behavior of dolphins (Orbach et al, 2020; Ramos et al, 2018a; Weir et al, 2018). Similar to other marine mammals (e.g., Hartman, van der Harst, & Vilela, 2020; Landeo‐Yauri et al, 2020), individual rough‐toothed dolphins can be identified by their scarring and skin pigmentation patterns. Future studies should focus on understanding the long‐term social structure of this species (stability of associations), in particular as it relates to cooperative foraging (e.g., prey sharing and group hunting).…”