Associate Professor Satoko S. Kimura and Ms. Maoko Shibata, a graduate student at the Division of Applied Biosciences, Graduate School of Agriculture, Kyoto University, together with their colleagues, have used drones (unmanned aerial vehicles, UAVs) to quantitatively estimate the body length of free-ranging wild narrow-ridged finless porpoises (Neophocaena asiaeorientalis) for the first time. Focusing on surfacing respiration behavior, we extracted moments when the body axis was closest to horizontal, and the distortion of the water surface was minimized, allowing accurate measurements. To convert pixel length in aerial images into real body length, we placed reference objects of known size on land and at sea and developed a scale-correction model accounting for flight altitude.

As a result, measurement error was very small (1.6–3.0%), and the coefficient of variation among repeated measurements from the same individual was only 0.7%, demonstrating high reproducibility. Estimated body lengths ranged from 93.8 to 168.0 cm, which is consistent with previously reported data from stranded individuals. This study provides the first quantitative description of body length distribution in wild narrow-ridged finless porpoises and presents a reproducible, standardized method for UAV-based morphometric measurements in small cetaceans. These findings are expected to play an important role in future assessments of health conditions and reproductive status, as well as in the collection of baseline information for conservation planning.

This study was published in Mammal Study on January 26, 2026.

Co-author’s Comments

“It seems we can observe animals much more clearly with drones.” — The advent of UAVs has ushered in an era in which cetaceans can be photographed easily and in remarkable detail. However, this study began with a fundamental question: how can we go beyond producing beautiful images and turn them into science? After securing research funding for this project, purchasing UAVs, and learning flight techniques and relevant regulations, the moment we first captured images of wild finless porpoises remains vividly memorable. In this study, we first tackled the challenge of measuring the body length of live, free-ranging individuals—something that had long been difficult to achieve. For our research team, this represents our first report using UAVs, and related studies are currently underway. We plan to report further findings soon! (Satoko S. Kimura)

Although finless porpoises are familiar to many people through aquariums, surprisingly little is known about their appearance in the wild due to the difficulty of observation. In particular, non-invasive approaches are essential for studying wild individuals, making it challenging to obtain even basic information such as body size. In this study, we estimated body size from an aerial perspective using UAVs. The method presented here is expected to provide valuable information for future ecological research and conservation assessments. (Maoko Shibata)

Publication Information

Researcher

Satoko S. Kimura　Activity Database on Education and Research, Kyoto University
Maoko Shibata　Graduate Student, Division of Applied Biosciences, Graduate School of Agriculture, Kyoto University

Related Information

“Visualization of Individual Relationships among Dugongs in Talibong Island, Thailand, Using Social Network Analysis,” Center for Southeast Asian Studies, Global Collaborative Research (R7 2–5)
Latest Research News: A Novel Detection Approach for Accurately Extracting Finless Porpoise Vocalizations and Vessel Noise

Contact

<About the paper>
Satoko S. Kimura, Associate Professor, Center for Southeast Asian Studies, Kyoto University
E-mail:  kimura [at] cseas.kyoto-u.ac.jp (Please replace [at] with @.)

<About the publicity>
Public Relations Committee, Center for Southeast Asian Studies, Kyoto University
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