In a First, Scientists Use Drones to Detect Pregnant Dolphins

Researchers say the new tech will help them better understand bottlenose dolphin reproduction

Aerial View of Dolphins
Bottlenose dolphins swim in the Moray Firth Special Area of Conservation off Scotland. The photo was taken by an aerial drone. University of Aberdeen

As marine biologist and ecologist Barbara Cheney looked out upon the waters off of Scotland, she was concerned.

Her team of researchers—from the University of Aberdeen’s Lighthouse Field Station and Duke University’s Marine Robotics and Remote Sensing Laboratory—had chosen this day in July 2017 to head out onto the open water and capture images and scans of bottlenose dolphins by way of drone because it was expected to have clear skies and calm waters. The water was still, but the team worried that morning about glare reflecting off the surface of the sea, which might impact a clean view of the species.

The team couldn’t dawdle because the dolphins might not stay long. The dolphins are a protected species living in a conservation area, and due to permitting the researchers had a limited amount of time to complete their work. Some ten minutes after taking to the water, the team reached a well-known dolphin hotspot in in the North Sea. There, they sat for some time, watching the cetaceans in the tranquil water before the team decided to risk taking shots that might be affected by glare, when Julian Dale, an associate in research at Duke and the team’s drone pilot, said, “Let’s give it a go.” Their goal: seeing if their drone data could to determine if any of the dolphins were pregnant.

Scientists from Aberdeen have been monitoring the bottlenose dolphin population in the Moray Firth Special Area of Conservation for more than 30 years, using photo identification of dorsal fins and their markings to identify individual dolphins and follow their progress. They have been able to measure the length of the dolphins with those photos, but without a bird’s eye view of the body, it was impossible to determine if a female was pregnant.

Aerial photographs from a drone and scans from a separate camera would provide researchers with visuals of the dolphins’ length and width, as well as the outline of their bodies and their markings; a pregnant mother would be much easier to identify.

“We really didn’t know if this was going to work,” Cheney says. “A lot of work with drones has been done either farther off shore or in tropical areas, where you get beautiful, clear waters.”

The researchers were operating their drone above temperate waters, which tend to be murky. Teams like Cheney’s usually only know whether dolphins were pregnant after the fact, by seeing calves with the mothers. As a result, failed pregnancies and calf deaths shortly after birth are rarely recorded. That information is crucial to understanding what environmental factors might be affecting reproduction.

Back on shore, Dale uploaded the drone-captured images to a computer for Cheney to see. As she waited, she felt tense. But when the photographs started to appear on the screen, she stopped worrying. The water was crystal clear and so were the images. The photos looked perfect for analysis.

With the use of drone technology, the researchers were able to gather enough information about the pregnancy status of these female bottlenose dolphins, a feat that had yet to be done with small cetaceans. These findings, published in February 2022 in Remote Sensing in Ecology and Conservation, could lead to breakthroughs in scientists’ understanding of bottlenose dolphin reproduction.

“Determining the pregnancy status of a species like the bottlenose dolphin is crucial as it can provide information on reproductive failure, which can further be linked to other parameters, like age of the female and environmental conditions,” says Séverine Methion, a research scientist at the Bottlenose Dolphin Research Institute who was not a part of the study.

Estimating pregnancy rates of dolphins

While this isn’t the first time drones have been used to study marine mammals—the technology has helped scientists learn more about the complex social lives of a group of killer whales in the Pacific Northwest—this is the first time they were used to look at much smaller cetaceans.

During the study, five boat-based surveys were carried out in July and August of 2017. They chose mid-summer knowing more dolphins would be present in the area and that any pregnancies would be far along. Because the bottlenose dolphins in the area are a protected population, the team not only had to be licensed to fly the drone, but also to be on the water with the dolphins, where they had a limited amount of time to gather the required data. Per Cheney, the researchers can only spend 20 hours per month capturing images.

As photographs were being taken, two lasers scanned the dolphin bodies, data the researchers used to calculate measurements back in the lab. The team identified 64 bottlenose dolphins. Using the body width-length ratios of the dolphins, the researchers correctly determined that 14 dolphins were pregnant. Just one that was thought to be not pregnant was actually carrying a baby.

Following the success of this study, the team plans to do another round of photo identification surveys this May, in addition to more drone surveys this July and August. With regular studies of the dolphin population they will be able to compare the data collected, giving them a more accurate picture of the progression of pregnancy and which environmental factors—like water temperature and availability of prey—might be affecting birthrate.

With more detailed information from regular drone studies, they’ll be able to spot blips in data much sooner than they have in the past.

“If we can do this more often,” says Cheney, “we might see the effects of declining prey, or increased disturbance, or anything like that, in a shorter time period and be able to do something about it before it’s too late.”

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