Morphometric measurements of Omura’s whales using consumer grade sUASs: a methodological study

摘要

Photogrammetry is a powerful tool for taking indirect measurements of free-ranging marine mammals, and small unmanned aircraft systems (sUASs) are expanding the ways in which these images for morphometric analysis can be collected. A sUAS allows for photographs and videos to be captured from highly controllable positions and orientations, largely untethered from the physical location and constraints of the operator. This flexibility allows researchers to study and record agile cetaceans which can exhibit unpredictable swimming behaviors, such as Omura's whales (Balaenoptera omurai). However, purpose built sUASs can be prohibitively expensive, require specialized expertise to operate, and require resources not available to many field biologists. Large multirotor aircrafts can require significant time and space for launch and recovery, and the vehicle can pose a hazard to those operating in its vicinity. By comparison, consumer grade unmanned aerial vehicles (UAVs), or drones, continue to become increasingly inexpensive, reliable, and compact. We tested seven commercially available UAV products from five leading consumer drone manufacturers and gauged their ability to be used at sea and for cetacean photogrammetry. These preliminary experiments informed our selection of equipment which we trialed during a targeted field expedition off the coast of Nosy Be, Madagascar. Over the course of a three week survey, we compared the efficacy of a consumer grade, off-the-shelf UAV with a custom solution of comparable size and price. Both sUASs were successfully able to collect data which translated to animal size measurements. We provide both specific guidelines for selecting, testing, and calibrating consumer grade UAVs to be used on ocean-based expeditions, as well as procedures for conducting morphometric analyses with the resulting data. Our data analysis procedures are based on established methods of morphemic analysis of cetaceans photographed in single still images. Our software is freely available for other to use and modify.