Leopard seal measurements derived from aerial drone photographs are as accurate as those taken manually, according to a study published November 29, 2017 in the open-access journal PLOS ONE by Douglas Krause from National Marine Fisheries Service, California, and colleagues.
Body measurements are key to managing populations of pinnipeds, as their condition can reflect prey availability, habitat quality, and the overall the health of marine ecosystems. Leopard seals eat a range of prey -- including krill, penguins, and Antarctic fur seals -- along the coasts of Antarctica, making their body condition likely a valuable indicator of ecosystem health. While manual body measurements are generally accurate, they are also challenging logistically and can be risky to both people and pinnipeds. Notably, taking measurements by hand entails sedating pinnipeds based on guesstimates of their weight, which for adult leopard seals is upwards of 400 kilograms.
To find a safer, simpler way of assessing pinniped body measurements, Krause and colleagues used drones to take aerial photographs of leopard seals on Livingston Island in the Antarctic Peninsula, where a seasonally resident population hauls out along the coast. The researchers compared known body measurements to those derived from aerial photographs, using 50 images of 15 leopard seals at a variety of altitudes, ground surfaces, and body positions.
The researchers found that aerial photographs can be used to derive accurate estimates of leopard seal size and mass. This suggests that drones could also provide a cost-effective, noninvasive way to assess body condition in other pinnipeds, which is important because tracking pinniped responses to environmental changes is critical to understanding and managing marine ecosystems.
Dr Krause added: "We continue to develop methods to gather the data we need to manage wildlife populations in a safer, non-invasive way. The drones help provide measurements that are just as good as, or better than, traditional field methods, but without the need to ever bother the animals."
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Citation: Krause DJ, Hinke JT, Perryman WL, Goebel ME, LeRoi DJ (2017) An accurate and adaptable photogrammetric approach for estimating the mass and body condition of pinnipeds using an unmanned aerial system. PLoS ONE 12(11): e0187465. https:/
Funding: Funding for this study was provided by NOAA Fisheries.
Competing Interests: I have read the journal's policy and the authors of this manuscript have the following competing interests: Co-author Donald J. LeRoi is the owner of Aerial Imaging Solutions LLC, which produces the APH-22 drone used in the experiments. His technical knowledge was invaluable to the design of the study, therefore he deserves co-authorship credit; however, he was not involved in the execution of the study, data analysis or interpretation and writing. As lead author of the study I certify to the editorial staff that he did not attempt to influence the results of the study in any way. And, this does not alter our adherence to PLOS ONE policies on sharing data and materials.