Space & Innovation

Laser 'Ruler' Measures Whale Sharks

A technique that combines lasers and photography provides a decent measurement of the largest fish in the world.

Like Dr. Evil from the Austin Powers movies, scientists from the Marine Megafauna Foundation really like freakin' lasers. But they aren't using them on ill-tempered sea bass, they're using them underwater to measure whale sharks, the largest fish in the ocean.

The results should give scientists a better idea of the whale shark population as whole and improve conservation and management for this globally threatened species.

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Back in 2011, Christoph Rohner and Simon Piercereported using a technique called laser photogrammetry on whale sharks.

The technique combines lasers and photography to get an accurate measurement of the whale shark. The lasers are used to project a known length - a scale bar - onto the body of the free-swimming fish at the same time it's photographed. Later, the photograph is analyzed and the length of scale bar is used to calculate the total length of the shark, which can grow to 65 feet.

Now the scientists have applied to the technique from the 2011 study to measure whale sharks in Mozambique and Tanzania to create a more comprehensive survey. The lengths were compared to the bodies of stranded individuals that were dissected and age-determined. The sharks measured between about 14 feet and 30 feet long.

Rohner and Pierce found two main things. First, they concluded that laser photogrammetry is useful for making routine measurements, but is not accurate enough to estimate growth rates over a short period of time, say one to three years.

These animals live upwards of 80 years and so using the laser technique to collect measurements of the same shark over a period of decades makes more sense.

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They also found that most of the whale shark swimming in the waters off Mozambique and Tanzania were juvenile males between 14 feet and 30 feet long. This begs the question as to where the females are, the small juvenile sharks -- those between 1.5 feet and 13 feet -- as well as the mature sharks, which typically measure between 30 to 65 feet.

Knowing where these animals spend their time could greatly improve conservation and management.

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