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Current numbers on big species such as blue whales are still very sketchy. Pic: BBC/Silverback films

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“Boats and planes can’t go everywhere, but satellites can.”

Ocean Health: Scientists count whales from space

7 November 18


UK scientists have demonstrated the practicality of counting whales from space.

The researchers have been using the highest resolution satellite pictures available. Even when taken from 620km up, this imagery is sharp enough to capture the distinctive shapes of different species.

The British Antarctic Survey (BAS) team will soon conduct an audit of fin whales in the Mediterranean. The first-of-its-kind assessment will be employing a computer program to search through the satellite data.

Waters north of Corsica, known as the Ligurian Sea, are a protected area for cetaceans, and the regional authorities want to understand better the animals' movements in relation to shipping to try to avoid collisions.

Previous studies have played with the idea of spotting whales from orbit, but with limited success.

This new approach from BAS has drawn on imagery from the WorldView-3 spacecraft operated by the American company DigitalGlobe. WorldView-3 is able to discern things at the Earth's surface as small as 31cm across. Only restricted military systems see finer detail.

"Satellites have improved so much with their spatial resolution," explained Hannah Cubaynes, who is affiliated to both Cambridge University and BAS. "For the first time we've been able to see features that are truly distinctive of whales, such as their flippers and flukes."

What have the scientists done?

Ms Cubaynes' team examined WorldView-3 photos in different parts of the globe, looking for fin whales in the northern Mediterranean; humpbacks off Hawaii; southern rights around the Península Valdés, Argentina; and Pacific grey whales in Laguna San Ignacio, Mexico.

These are all baleens (filter feeders) and among the biggest cetaceans, reaching up to 15m or 20m in length.

The animals are detected just below, or even breaching, the sea surface. The fins and greys proved to be the easiest to identify in the pictures, in large part because their body colour contrasts well with the surrounding water and because they tend to swim parallel to the sea surface.

But, crucially, the team was able to make out the body shapes associated with the different animals, proving satellite-identification is a viable technique.

Why count whales from space?

Currently, most surveys are conducted from the air, from boats and sometimes from a promontory, such as a high sea-cliff. But these are very localised searches, and whales are known to range across hundreds of thousands of square km.

Some of their feeding grounds will be far from land. Without more effective means to track the animals, we cannot really say how well they are recovering after centuries of over-exploitation.

"This is a potential game-changer - to be able to survey whales unhindered by the cost and difficulty of deploying planes and boats," said Dr Jennifer Jackson, BAS's top whale expert.

"Whales are a really important indicator of ecosystem health. By being able to gather information on the grandest scales afforded by satellite imagery, we can understand something more generally about the oceans' health and that's really important for marine conservation."

 - AUTHOR: JONATHON AMOS

 - SOURCE: BBC SCIENCE & ENVIRONMENT

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