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British scientists have shown that it is convenient to count whales from space.
British Antarctic Survey (BAS) researchers use the highest resolution satellite images available.
Even taken from 620 km, these images are sharp enough to capture the distinctive forms of different species.
The team will soon conduct an audit of fin whales in the Mediterranean.
The first assessment of this type will be partially automated using a computer program to search for satellite data.
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BBC / Silverback Movies
Current numbers on large species such as blue whales are very basic
The waters north of Corsica, known as the Ligurian Sea, constitute a protected area for cetaceans and regional authorities wish to better understand the movements of animals related to navigation in order to avoid collisions.
Previous studies have played with the idea of spotting whales in orbit, but with limited success.
This new BAS approach is based on images from the WorldView-3 satellite operated by the American company DigitalGloble.
WorldView-3 is able to discern objects as small as 31 cm on the surface of the Earth. Only restricted military systems see the details finer.
"The satellites have improved so much with their spatial resolution," said Hannah Cubaynes, affiliated with both the University of Cambridge and the BAS.
"For the first time, we have been able to discover some truly distinctive features of whales, such as their fins and their ladies."
At a resolution of 31 cm, species identification becomes much easier
What did the scientists do?
Ms. Cubaynes' team examined photos of WorldView-3 in different parts of the globe, looking for fin whales in the northern Mediterranean. bumps off Hawaii; southern rights around Península Valdés, Argentina; and Pacific gray whales at Laguna San Ignacio, Mexico.
They are all baleen (filter filters) and among the largest cetaceans, reaching 15 or 20 m long.
Animals are detected just below or even across the sea surface. The fins and grays have been found to be the easiest to identify in the photos, largely because their body color contrasts well with the surrounding water. and that they tend to swim parallel to the surface of the sea.
Most importantly, the team was able to identify body shapes associated with different animals, proving that satellite identification is a viable technique.
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2018 DigitalGlobe, a Maxar company
WorldView-3 produces the clearest images in the public domain
Why count whales from space?
Currently, most surveys are conducted by air, from boats and sometimes from a promontory, such as a high cliff. But they are very localized research, and we know that whales extend over hundreds of thousands of square kilometers.
Some of their feeding areas will be far from the land. Without more effective ways to track animals, we can not really say how much they are recovering from centuries of overexploitation.
"It could change the game: being able to monitor whales without being bothered by the cost and difficulty of deploying planes and boats," said Dr. Jennifer Jackson, BAS Whale Protection Expert. .
"Whales are a very important indicator of ecosystem health, and by gathering information at the largest scales offered by satellite imagery, we can understand something more general about oceans health and how Is really important for marine conservation. "
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Rose Cole
Counting boats and planes works – but only on small areas
Do not we already have the smallest animals in orbit?
This is true to a certain extent. BAS has already been a pioneer in the use of satellite imagery to monitor penguins and albatrosses, for example. But there are crucial differences.
In the case of penguins, it is not really individual birds that are counted; it is rather the general size of a colony that is valued from the black mass of animals huddled against each other on their ice habitat.
And in the case of albatrosses, scientists know exactly where to look because bird breeding sites are limited to a handful of compact locations. A nest is just big enough to appear on a satellite image, which helps to estimate the likely number of albatross pairs.
Space ships will gather huge bands of images as they fly over the ocean. With the exceptional resolution now available, counting individual whales becomes practical. For example, in an image with a resolution of 31 cm, the moat of a gray whale will occupy 10 pixels.
Fin whale: the color contrast facilitates their identification
Where do these searches go next?
The team is currently testing different algorithms to automatically search for satellite images.
The best will soon be applied to a WorldView-3 dataset covering the Ligurian Sea.
"The total area is 36,000 km2, which is too big to perform a manual search," said Dr. BAS's co-investigator, Peter Fretwell. "It's a marine protected area and the worry is that there is a lot of sea traffic between Corsica, Italy and France.
"They are concerned about collisions with ships and we may be able to obtain information on the behavior of fin whales that will be useful to ship captains."
Satellites continue to improve. DigitalGlobe, for example, provides a new constellation that promises to dramatically increase the acquisition rate of high-resolution images.
Combined with the latest data analysis techniques, this should be a boon for marine biologists and ecologists.
They will not only get more robust figures for live whale populations, but they should also have a much better idea of the number of dead animals stranded on the distant coasts of the world.
Ms. Cubaynes and her colleagues published their research in Marine Mammal Science.
[email protected] and follow me on Twitter: @BBCAmos
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