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| Earth on Nov 22, 2011

Juliet Eilperin on the hidden world of sharks

The author of Demon Fish talked to EarthSky about what scientists are learning about sharks.

People are fascinated by sharks, but scientists still have a lot to learn about them. That’s according to Washington Post science reporter Juliet Eilperin, whose new book on sharks is called Demon Fish. The book was released in June 2011. She told EarthSky:

What’s happened is that there have been advances in technology particularly in terms of tracking, satellite tagging, things like that, that have allowed scientists to get a better sense of all sorts of shark behavior.

Image Credit: Thespis377

She said that, for example, scientists studying great white sharks off the U.S. Pacific coast have been able to identify with precision how many sharks are living there and their pattern of migration to the Hawaiian islands.

We have learned that they have as regular migrations as wildebeest in Africa, or elks traveling on land. They’re much more directed than we realized before. In addition we simply had no idea how many whites were out there.

As it turns out, there are about 300 great white sharks out in the Pacific, which is fewer than scientists expected, Eilperin explained.

The earth’s surface is magnetically polarized, which is why our own compasses work. Sharks have a built-in compass, called electroreception, that allows them to migrate long distances and navigate the magnetic underwater highways of the earth.

Sharks can go out hunting at night, following the patterns, find food, and find their way back home, and they shift where they go, when the magnetic patterns of the Earth shift.

Image Credit: Serge Melki

Eilperin told EarthSky that sharks are threatened worldwide by human activity – especially an appetite for shark fin soup, a delicacy throughout Asia. Sharks are also getting caught in fishing nets intended for tuna. She said:

You’re talking conservatively about between 80 and 100 million sharks being killed each year …

She added that if more people knew how closely humans and sharks are related, we might have a stronger desire to protect them. She said:

People might not know this, but in fact the muscles that we use to chew and to talk come from sharks, originally, and so I think understanding that there’s an evolutionary connection between humans and sharks is something most people never think about.

Sharks have so many incredible adaptations, so it’s hard to pick just a few. But I would name their electroreception, the idea that they can detect electrical currents underwater and this allows them to do everything from sense that a fish might be flailing, in trouble, under the sand, and ferret it out, to the idea that hammerheads can navigate the magnetic underwater highways of the earth.

Eilperin’s personal favorite shark is the Cookie Cutter shark. She explained why:

This is another example of how we didn’t understand something for a while. It’s only in the past decade that we’ve learned how these relatively small sharks manage to take literally cookie-sized bites out of tuna, or big fish. And it turns out that they have this incredible bioluminescence, they have a glow underwater. Some parts are light, some are dark.

It’s a particular pattern of glow, she explained – kind of like a camouflage made of light.

And somehow, for the bigger fish swimming above, it tricks them into thinking that the cookie cutter shark down below isn’t a predator, but a school of small, non-threatening – and tasty – fish. So the bigger fish, the tuna, approach [the sharks] without fear. And the sharks can leap up.

They leap up, and take a cookie-sized bite of tuna flesh.

I think that’s a fantastic evolutionary development they’ve managed to master.

This was discovered in the late 90’s. Until then, scientists had no idea how small cookie cutter sharks managed to take on tuna, which were so much larger than them.

Eilperin explained why sharks, despite their cleverness, are so vulnerable to overfishing by humans.

Sharks are in danger in a way we’re just beginning to realize. For the most part, they take longer to mature sexually, they take longer to reproduce, and when they do, they usually have a small number of offspring.

She said there are a few different thoughts on how best to conserve them:

One of the main ways to provide a safer place for sharks is the establishment of marine reserves. You’re seeing leaders from many countries take this one. There’s a growing interest in creating places that are off-limits to fishing. For example, the Bahamas is on the cusp of banning shark fishing altogether. In Chile, they’re getting close to passing legislation that would mandate that when you bring a shark in from the sea, you have to have its fins attached. And in the U.S., some states are going straight after the consumption of shark fins, approaching it more from the supply side.

Really, shark survival is essential to our survival. If sharks really disappear, what you’re talking about is a potential collapse of major ecosystems that we depend on for sustenance as well as enjoyment, as well as our conception of what the world is.

Listen to the 90-second EarthSky interview with Juliet Eilperin on what scientists are discovering about the hidden world of sharks (at top of page.)