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Why More Sharks Don't Invade Freshwater Lakes and Rivers


Why More Sharks Don't Invade Freshwater Lakes and Rivers | IFLScience

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But what about the density differences between seawater and freshwater? After all, one of the most noticeable differences (for us at least) between, say, the Great Salt Lake or the Dead Sea and a swimming pool is how well we can float. While many bony fish have swim bladders to help control their buoyancy, the primary source of buoyancy in elasmobranchs is a lipid-rich liver.

So, Stanford’s Adrian Gleiss and colleagues designed a hydromechanical model based on the bull shark (Carcharhinus leucas), one of the few elasmobranchs that live in freshwater for part of their life cycle. They found that being in freshwater would lead to a two- to three-fold increase in negative buoyancy for sharks and rays—which carries the energetic cost of increased drag because they have to lift themselves. 

Sharks could try to compensate for this increased negative buoyancy, but then the lipid-rich liver would need to be eight times bigger by volume in order to maintain the same net buoyant effect they’d enjoy in marine waters. 

Not sure what thus is saying. Sharks have trouble staying afloat in fresh water?

Yes.  Fierce but floundering.

Heh.

Sweet, I will no longer fear sharks in fresh water!

No worries!

The suspense-filled premiere "American Killers" follows Wade as he treks across the United States in search of deadly river monsters living in the nation's waterways — from the popular Indian River Lagoon in Florida, where unsuspecting water enthusiasts are faced with what could become a modern day Jaws, to the Lake of the Ozarks in Missouri, where underwater hunters have reached man-eating proportions. Other U.S. locations include Barbers Hill Canal and the Trinity River in Texas as well as the creeks and lakes of Oklahoma.

"I've been on the trail of river monsters all over the world, and normally I'm tracking them down in remote jungles. However, lately I've been getting reports from an area I couldn't believe, one of the most populated places on earth — the United States," says Wade. "I've discovered that you have to learn to expect the unexpected in my business, but what viewers will see in 'American Killers' took even me by surprise."

http://www.animalplanet.com/tv-shows/river-monsters/about-this-show/about-river-monsters/

Ever watch the show? Any good?

AWESOME show.  I liked the episode about the man-eating sawfish.  Big ol' SAW - on a fish. 

Yikes, you're not kidding!

sawfish

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