How do you count whales? If you’re flush with money, you might be able to hire out a plane, but normally you’d have to stand on the shore with a pair of binoculars and scan the water. Whilst simple, cheap, and effective, it’s limited in what information you can glean from the mammals as they migrate up the coast. Thus, in swoop the drones.
Scientists from NOAA Fisheries have for the first time employed unmanned aerial vehicles to help them count and monitor the gray whales as they swim from their birthing grounds in Baja California, Mexico, up to the Arctic where they spend their summer feeding. With drones hovering above the whales as they pass by during their epic migration, scientists in the state of California are able not only to count, but also to estimate the size of the mega mammals.
“By studying the body condition of females, we hope to connect the dots between conditions in the Arctic one year and calf production the next,” explained John Durban, a marine biologist from NOAA Fisheries. “Ultimately, we're trying to understand how environmental conditions affect the reproductive success of the population.”
The hexacopter coming in to land. Credit: NOAA
Nearly hunted to extinction during the last century, the eastern gray whale (Eschrichtius robustus) population has recovered to around 20,000 individuals. Now that their main threat of hunting has largely been stopped, scientists are keen to understand what other factors influence the ups and downs observed in their numbers.
One way of doing this is to count how many mothers and calves pass by California on their way up to the chilly waters of the Arctic. Whilst this gives some indication of the population’s health, it’s only a crude measure and doesn’t provide the full picture. By estimating the size of the females, however, the scientists are able to judge how much blubber she’s packing, and thus how well she fed the summer before.
By hovering the drone at the same height above each pair of mother and calf, at least 36 meters (120 feet) to avoid disturbing them, the researchers can then analyze in the lab the images taken of the whales and calculate the length and girth of the mammals down to a few centimeters. “We can't put a gray whale on a scale, but we can use aerial images to analyze their body condition—basically, how fat or skinny they are,” said Durban.
They were able to find 60 mother and calf pairs over the season, and hope that the success of this analysis could be applied to other large whales and how the environment puts an upper limit on their population growth. Understanding this will help the scientists determine what are normal population fluctuations, and what more serious declines look like.
