Marine biologists in Scotland have found an innovative way to determine whether the bottlenosed dolphins they’re studying are pregnant: They’re collecting photogrammetric images of the dolphin females’ developing bodies using camera images captured by aerial drones. The project is a joint venture of University of Aberdeen researchers based at the Lighthouse Field Station in Cromarty in collaboration with Duke University’s Marine Robotics and Remote Sensing Laboratory (MaRRS). It’s the first known study of birth patterns among female bottlenose dolphins using non-invasive techniques, and it promises to tell researchers more than they currently know about the marine conditions that affect dolphin survival and reproduction.
Aerial drone studies of sharks in South Africa and sea turtles in Costa Rica have proven effective in monitoring their seasonal migration and mating patterns. But few researchers have tried to use drones to track individual members of a sea mammal community up close and over time. The biologists at Aberdeen have been studying the bottlenose dolphins at the Lighthouse Field Station for over 30 years. In this study they used aerial video surveillance cameras to measure the body length and width of 226 dolphins over a single mating season and compared their results to those obtained using laser cameras mounted on boats. The drones accurately predicted which dolphins were pregnant 93% of the time.
The researchers were able to match data on successful and failed dolphin pregnancies to a variety of marine environmental conditions, including access to food, to better assess how and why the population was growing. The researchers had made such broad assessments in the past but had not linked dolphin growth and survival patterns to reproduction success specifically.
Dr. Barbara Cheney, a Research Fellow at the University of Aberdeen’s School of Biological Sciences who is based at the University’s Lighthouse Field Station, noted: “Previously we only knew if female bottlenose dolphins were pregnant if they were later seen with a calf. As a result, we only knew about successful pregnancies, and didn’t know how many pregnancies failed or how many calves died before we saw them.”
Earlier studies have tracked the population patterns of larger cetaceans, including blue whales, with the assistance of aerial drones. However, in the current study, researchers were able to track individual dolphins based on past identification and through continuous close observation. The drones were launched by hand from boats and flew no more than 100 feet above the dolphins as they swam in the area of the Research Station. The Duke teams’s high-powered long-range video surveillance cameras equipped with sophisticated sensors were able to track the dolphins as they dove below the surface and reemerged. About six images per second were filmed. It helped that the drone’s remote pilot had extensive experience tracking sea mammals in past marine biology research investigations.
The results of the most recent study, co-authored by Cheney, were published in the February 2022 issue of Remote Sensing in Ecology and Conservation.