Eric Hopton for redOrbit.com – Your Universe Online
How does a scientist measure blubber on a living wild whale? It used to be an estimation at best, using a pair of binoculars trained on a distant whale. Now, biologists have a cool new technique that is far more accurate: an unmanned hubcap-sized “hexacopter” with six rotors that can track and image whales from directly above.
For 22 years, John Durban, a marine mammal biologist from the US National Oceanic and Atmospheric Administration (NOAA) used binoculars to monitor migrating gray whale mothers and their calves off the Californian coast.
Though Durban and his NOAA colleagues still use binoculars, the hexacopter is far more accurate. The team will use the advanced data to work out what causes annual fluctuations in the numbers of mothers and calves.
The hexacopter hovers at around 120 feet, capturing “straight-down photos” from a digital camera in its belly. It also carries a very precise pressure altimeter, allowing scientists to measure the exact altitude at which each image was taken, which in turn means they can accurately calculate the length and girth of the whales within a few centimeters. This in turn gives them an accurate measure of how much blubber the animals carry.
“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,” Durban said.
A tough journey
The mother gray whales fast for most of their long migration while they nurse their calves. Without plentiful blubber reserves, the mother may not be able to support her calf.
In good feeding years this is no problem. But, in the lean years, fewer calves will be born, and fewer still will survive the migration.
“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,” said Durban. “Ultimately, we’re trying to understand how environmental conditions affect the reproductive success of the population.”
Gray whale success story
The rarity of most other large whales means that scientists have found it hard to study these dynamics in action. The US population of gray whales, however, has recovered from being close to extinction to the point where they were taken off the endangered species list in 1994, and now they offer scientists a unique opportunity to study large whale ecology.
The NOAA team hopes their study will reveal how environmental conditions put an upper limit on population growth. “With gray whales, we’re just beginning to understand what a recovered population of large whales looks like,” Durban said. “We’ll have to get used to seeing recovered populations have good years and bad years,” Durban said. “That’s what happens when you’ve recovered and you’re hovering around a food ceiling.”
This will help scientists set recovery goals for other species and to distinguish between normal population fluctuations and signs of a more serious decline.
“Hopefully in the not-too-distant future,” Durban said, “there will be many healthy populations of large whales to study.”
Check out the latest counts here and the video “Born to migrate” here.
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