Drones record hundreds of whales in Pacific, revealing ‘novel insights,’ study finds

For years, drones have zipped over the coastlines of Hawaii and Alaska, tracking one of the world’s largest creatures: humpback whales.

Flown by scientists, the aerial vehicles snapped photographs of hundreds of migrating pairs of mothers and calves in hopes of demystifying the species’ life cycle.

Now, after the photos have been analyzed, several “novel insights” have been revealed, according to a study published on Dec. 12 in The Journal of Physiology.

Namely, scientists documented dramatic changes in the size of the mothers and calves and in humpback birth rates.

Changes in size

Between 2018 and 2022, “a total of 2,410 measurements were taken from 1,659 individuals, with 405 repeat measurements from 137 lactating females used to track changes in maternal body volume over migration,” Martin van Aswegen, one of the study authors, said in a news release from the University of Hawaii at Manoa.

The findings revealed that new mothers lost a significant amount of body size over a short time.

In six months, they decreased in body volume by 17% on average. Specifically, the mothers off Hawaii — where the whales breed — lost about 214 pounds of blubber each day.

Comparatively, non-pregnant and pregnant females off Alaska — where the whales feed — gained size much faster than new mothers, putting on weight between two and six times the rate of lactating females.

Calves, in contrast, rapidly put on weight. They increased their body volume by about 395%, and their length increased by nearly 60%.

“The surprising part of this study was our ability to find the same individual mothers and calves over great distances and time periods,” van Aswegen said. “To measure the same whales over 3,000 miles apart over a period of roughly 200 days is truly remarkable and provides such valuable data for the questions we were asking.”

Drop in birth rates

The study indicated that birth rates have declined precipitously in populations off Hawaii and Alaska.

Between 2015 and 2016, birth rates off Hawaii shrunk by 80%, while the rate of mother-calf encounters decreased by 76.5% between 2013 and 2018.

Meanwhile, off the coast of The Last Frontier, there was “a total reproductive failure in 2018.” And between 2014 and 2019, the calf survival rate shrunk by tenfold.

“These observations coincided with the longest lasting global marine heatwave, which shifted food webs and reduced availability of prey throughout the North Pacific,” according to the release.

While the heatwave lasted, the whales likely were not able consume enough food, leading to nutritional deficits and less reproduction.

These declines in reproduction provide “additional urgency” for understanding the relationship between mothers and calves.

“This work forms the basis for future studies investigating the energetic demands on humpback whales,” Lars Bejder, one of the study authors, said in the release.

“Our humpback whale health database, comprising 11,000 measurements of 8,500 individual whales in the North Pacific, is being used across several projects within the Marine Mammal Research Program and abroad,” Bejder said. “These studies will be used to better predict the resilience of large baleen whale species in the face of threats, including disturbance, entanglement, vessel collision, and climate change.”

In addition to van Aswegen and Bejder, the study authors were Andy Szabo, Jens Currie, Stephanie Stack, Lewis Evans, Janice Straley, Janet Neilson, Christine Gabriele, Kelly Cates and Debbie Steel.

This story was originally published December 27, 2024 at 12:31 PM with the headline "Drones record hundreds of whales in Pacific, revealing ‘novel insights,’ study finds."