Sharks circling at National Aquarium

Sharks are circling at the National Aquarium where Shark Week is a thing. Researcher Alan Henningsen and reporter Sarah Kaplan visit the aquarium's shark population and discuss the adaptations that make sharks so fascinating.

Posted by Washington Post on Tuesday, July 25, 2017

Yeah, we know, “Shark Week” is pretty disappointing. No, the shark that Michael Phelps “raced” was not real. No, a giant prehistoric shark called a megalodon doesn't continue to prowl the seas. Sure, there is some awesome science thrown in there with the bogus “voodoo shark” stories. But basically, the week is a multimillion-dollar marketing ploy masquerading as educational programming.

But! We really, really, really like sharks. So we're not above shamelessly exploiting the Discovery Channel's gimmick to share our favorite fun facts about these brilliant and bizarre creatures. The best part is, these are all true.

Sharks are ancient: The first sharks evolved more than 400 million years ago, long before mammals, dinosaurs and flowering plants. They have survived at least four mass extinctions, including one that killed off 90 percent of all species on Earth. More than 500 shark species are still around. They range from the dwarf lanternshark, which is no longer than a pencil, to the whale shark, which can be as big as a school bus.

They have no bones: Sharks, along with their close relatives rays and skates, are distinguished from other fish by their cartilaginous skeletons. The stuff that forms the framework of their bodies is the same rubbery tissue that makes up our noses and ears. This makes their skeletons light and flexible and makes sharks the swift swimmers that they are.

They have awesome names: The biologists who came up with the names for some sharks were seriously having fun. There's Megachasma pelagios, or the “giant mouth of the deep” — a rarely spotted filter feeder the size of a U-Haul. There's the scalloped bonnethead, which sounds as if it's a clothing item in “Pride and Prejudice” but looks like it belongs in “Pride and Prejudice and Zombies.”

Then there's the aptly named cookiecutter shark, which latches onto its prey and uses serrated teeth to cut a perfectly round chunk of flesh from its victims. Cookiecutters also use bioluminescence and color contrasts to mimic the silhouette of small fish and lure other ocean creatures close enough for the little shark to grab a bite. The characteristic pockmarks from a cookiecutter attack have been found on whales 50 times their size. Never mess with a cookiecutter.

Their sixth sense is electric: Sharks are capable of electroreception. Using jelly-filled cells called ampullae of Lorenzini, they can detect the disturbances in Earth's magnetic field generated by the movement of animals and waves. Saltwater is an amazing conductor of electricity, and the ampullae of Lorenzini are so sensitive that a shark could theoretically detect the current from a AA battery 1,000 miles away.

Lady sharks don't need a man: Some shark species are capable of parthenogenesis — the females can give birth without ever meeting a male. The process involves mama sharks doubling their eggs' genomes, essentially cloning themselves. Several years ago, a swell shark at the National Aquarium in Baltimore produced five pups this way. She hadn't encountered a male of her species for at least three years.

Baby sharks are hardcore: Several species of shark are ovoviviparous — the mother retains her eggs inside her body, and her pups hatch and develop in her uterus. But sand tiger sharks, which dwell in warm and temperate waters around the world, take it one step further. They practice in-the-womb cannibalism, or “adelphophagy” — literally “eating one's brother.” During gestation, the biggest embryos devour their litter mates until only two are left alive. The is actually advantageous to their mom, because it means she gives birth only to the strongest and fiercest young, who are then more likely to survive in the wild.

Looking for more amazing shark facts? We visited the National Aquarium on Tuesday to talk with fishes research specialist Alan Henningsen about what makes these animals so special. Watch the video at the top of this post to hear what he had to say.

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