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Needcoffee’s Shark Week: Day Three

Sharks of the World Princeton Field Guide

Expanding on the idea presented yesterday that there are other sharks besides the Great White, I think we should explore the variety of shark species a bit further than biggest and smallest. This could take a very long time, of course, so over the next few days we’re only going to explore a few facts each about the first fifteen species that popped into my head. To help you study many, many more species of sharks in a much more organized fashion, I would like to recommend Princeton Field Guide’s Sharks of the World. This book is a very comprehensive guide to over 400 species of sharks with drawings and pertinent facts for each one, and much more of a scientific field guide than a casual reading book. If you really want to be able to identify which of the three thresher shark varieties you’re looking at, this might just be the book for you. Shark geeks like me can buy it here!

First, we have a familiar face (or silhouette, if you prefer): the Hammerhead Shark

Hammerhead shark

Image: Kris-Mikael Krister via CC 3.0 license. Resized.

  • There are nine separate species of hammerhead sharks, including the more round-headed bonnethead sharks.
  • Scientists believe that the odd shape of the shark’s head helps it pick up the electrical signals of its prey more easily.
  • Recently, a hammerhead gave birth to a pup that had no paternal DNA; in essence, a virgin birth (and the first of its kind documented in any shark species)!
  • Hammerheads are more intelligent than most sharks; some species swim in schools and have more social communication than most other types of sharks.

Next on the list is an animal that is not as famous as the hammerhead, and also is very different: the Angel Shark.

Image: Nick Long via CC 2.0 license. Resized.

  • Angel sharks are bottom feeders and bury themselves in the sand in order to camouflage themselves and ambush their prey of small fish and crustaceans.
  • Because they are bottom feeders and cannot swim to keep the water flowing over their gills to breathe as do many other sharks, they have specially adapted muscles to do this for them.
  • They were not fished commercially until the 1970s, when an enterprising fisherman started saying “Wow, these sharks are tasty!” (not a direct quote) As a result, some species are on the endangered list and a few have been totally eliminated from particular fishing grounds.
  • These sharks not only look like rays–their egg cases also resemble those belonging to rays, which are sometimes called a “mermaid’s purse” because of its shape.

Perhaps one of the weirdest sharks out there is the Cookie Cutter Shark.

Cookie Cutter Shark

Image: Smithsonian.

Imagine you are a largish fish, like a tuna, or even a dolphin. You’re swimming around when you see this little tiny fish, just waiting to be your lunch. As you move in to snatch it up, however, it suddenly turns into a much bigger fish that bites a chunk out of your side and swims away! The nerve!

Cookie cutter sharks (also known as cigar sharks from their shape and color) are basically parasites to larger fish. They have a bioluminescent belly, which blends in with the water above them and makes them appear invisible from below, except for one small patch of dark, thereby fooling would-be predators into thinking it is small and helpless. When the bigger fish comes in for the kill, the rest of the shark goes in for its meal, making a very neat “cookie cutter” hole in its prey with its small, razor-sharp teeth.

Lest you run in fear thinking that this will happen to you, these sharks live really deep underwater and have not been known to attack humans at all because of this. So unless you’re diving down a thousand meters, I wouldn’t worry too much. The animals that they score a meal off of most often survive, albeit with a really cool scar to show their friends. One human-related thing they have been known to attack are the rubber pieces of sonar equipment on submarines, which have had to be repaired and replaced due to the cookie cutter sharks. The sharks were probably pissed off when they realized it wasn’t fish they were eating.

Image: Thomas Alexander via CC 4.0 license. Resized/cropped.

Thresher Sharks are closer to the “stereotypical” shark shape that one tends to think of, except for their fabulously long tails (or caudal fins, as I should say), whose graceful movement makes them one of my favorites.

  • A thresher’s caudal fin may be up to 50% of its body length. It uses the tail as a whip on or in the water to scare schools of fish tighter together (making a more compact meal) and stunning fish to capture them more easily.
  • Occasionally, a thresher shark may jump completely out of the water, breaching like a dolphin or whale does.
  • Although thresher sharks are dwindling in numbers and classified “vulnerable to extinction,” they are hunted for their meat, oil, skin, and also (as I was disturbed to find while looking for images), as a sport fish.
  • Threshers are rather shy and gentle, and other than unintentionally smacking people with its tail (well, wouldn’t you if you had a tail the same length as the rest of you?), it rarely bothers people.
Lemon shark

Image: Albert Kok via CC 3.0 license. Resized.

Yay for Lemon Sharks! Why are lemon sharks so cool? It’s not because they smell lemony fresh — they’re not the secret ingredient in Pledge — they get their name from their yellow-brown coloring.

  • Yay because lemon sharks are one of the most commonly used species for scientific research because they do really well in captivity, unlike some other species. So next time you hear about a shark study helping to learn about the prevention of human degenerative diseases or cancer, say a little thank you to the lemon shark.
  • Dr. Eugenie Clark (of Shark Lady fame, whom I introduced on Day One) is often asked if she has ever been bitten by a shark in her many years of field research. Apparently, this has only happened once. She was in her car driving with the jaws of a lemon shark on the seat beside her. She had to slam on her brakes very quickly during the journey, and reached her arm out so the jaw wouldn’t be damaged, inadvertently getting “bitten” by the teeth. Well, if you have to get bitten once…
  • Juvenile lemon sharks have nurseries in mangrove swamps to protect them until they get big enough to fend for themselves. Because of the oxygen-poor environment and murky conditions, the young lemon sharks grow up with better eyesight and oxygen-efficient gills than their brethren in the open ocean.

More fascinating sharks tomorrow, I promise! So stick around, have a cup of coffee, and think happy sharky thoughts.

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