U.S. researchers say an unmanned aerial vehicle carrying a high-resolution camera has allowed them to follow families of killer whales as the animals swam, played and -- sadly, in two cases -- died in the Pacific Ocean.

The record of the life happenings of orcas was captured in the Johnstone Strait off of British Columbia, scientists from the National Oceanographic Administration and the Vancouver Aquarium reported.

During a 13-day scientific mission in August, a specially-built aerial drone hovered 100 feet over the orcas, gathering images of 82 different whales.

One goal of the mission was to see if the creatures where getting enough to eat, determined by how fat or how skinny they were.

British Columbia's northern resident killer whales have been identified as threatened under the Species at Risk Act of the Canadian government.

One of the killer whales photographed by the drone, dubbed A-37, was so skinny the researchers were concerned about its ability to survive, a concern that turned out to be justified.

"It really doesn't have any fat behind the skull that we're used to seeing," said NOAA's Southwest Fisheries Science Center biologist John Durban in describing an image captured of A-37. "It's a skeleton with skin over it."

"We flew over him a couple of times and got these incredible images, and then while we were up there, he disappeared and he stopped swimming with his brother and has almost certainly passed away," he said.

Similar weight loss was noted in another orca, I-63, a female that lost a calf earlier in the year, the researchers said.

"Her subsequent death made us wonder if she had been sick or injured," Lance Barrett-Lennard of the Vancouver Aquarium's Marine Mammal Research Program wrote in a blog post.

The orcas main diet is salmon, and researchers note that the salmon runs the animals depend on are generally smaller than they used to be and the lack of prey could be limiting whale populations.

Every summer researchers conduct a census of the orcas in an attempt to determine how many whales may have died since the previous year.

"But mortality is a pretty coarse measure of how well the population is doing because the problem, if there is one, has already occurred," says John Durban, a biologist with NOAA's Southwest Fisheries Science Center in La Jolla, California. But the hexacopter, Durban said, "can give us a more sensitive measure that we might be able to respond to before whales die."