Welcome back! Today we're wrapping up our exploration of fifteen different species of sharks. To catch up on the previous ten (and the rest of our Shark Week posts), go here. We have a few "normal"-looking sharks, and then a few weirder ones. But first, let me introduce today's book choice. I admit that even though I am indeed an adult, I love DK's illustrated children's books. Oh, they have great books for grownups, too, but I still enjoy the way they can pack so many pictures and so much interesting information in a straightforward (but not boring!) way into a book for kids. And no matter how much I think I know about a topic, they always seem to have at least one thing I did not know before I picked up the book. Therefore, today's choice, particularly for those of you out there with kids, is the DK Eyewitness book Shark. You can grab it here.
A beautiful species often seen in aquariums is the Zebra Shark. Although the shark has spots, naming it after the zebra isn't actually as crazy as it sounds. When they are juveniles, these sharks have zebra stripes, black and white. As the shark reaches adulthood, however, the stripes change to spots. This leads the zebra shark to be erroneously called a "leopard shark," which is actually the correct common name for a different species.
- Like the Thresher Shark, the caudal fin of zebra sharks is extremely long. They use their elongated body shape to squeeze into small crevices to find food. This works especially well for them because they are slow swimmers and would not be as successful in chasing down their prey.
- Although these sharks, like other bottom-feeders, don't have to swim constantly to keep water flowing over their gills, they tend to face the current so that they don't have to work quite as hard to pump water over their gills all the time.
- Female zebra sharks lay egg cases from which the baby sharks hatch. The egg cases have hairs all over them to keep them in place after they are laid. And the mama sharks hide them so well that scientists still aren't sure where they are born. Some marine biologists think they must hatch in very deep water, and some have observed juveniles congregating in shallow water around India, which leads them to believe this might happen in other areas with zebra sharks.
Last Spring, new Zebra Shark pups were hatching at the Georgia Aquarium. They have a webcam of the shark pups here. When the webcam is offline, you can still look at the great still shots they have.
Image from the Georgia Aquarium.
Not much is known about the Ragged-Tooth Shark. This is due somewhat to the fact that until very recently, biologists had a very hard time narrowing down the species. All over the world, people were identifying similar sharks as different species, confusing how many different kinds of ragged-tooth sharks there were. Finally, the diligent studies of Leonard Compagn (who looked through museum specimens and grouped like sharks together) narrowed the species down to two: the Bumpytail Ragged-Tooth and the Bigeye Ragged-Tooth. (Thanks to ReefQuest Centre for Shark Research for this fascinating story.) What we do know, however, is very interesting...
- Baby ragged-tooth sharks are a meter long when they are born, which helps them survive better than smaller sharks.
- The ragged-tooth shark was the first shark to be protected by law when over-fishing threatened them.
- These sharks often swim in schools, hunting together to improve their chances for a meal.
This video from Save Our Seas is the story of Maxine, a ragged-tooth shark who was extremely lucky to escape death twice in the space of three months. After a stay in the aquarium that saved her from a stray sport-fishing hook, she was released back into the wild, and hopefully will help her rescuers learn more about "raggies."
Image taken from MSN Encarta.
The Megamouth Shark is extremely rare. Discovered in 1976, there are only 38 recorded specimens (it's really weird to read about them and have "specimen 7" referenced--it just makes you realize how few have been studied). For a closer look at where they were found and for photos of most of them, Sharkman has a great page up.
Megamouths live very deep, and are occasionally caught inadvertently in deep-fishing nets. They are filter feeders, like the whale shark and basking shark. Based on the information from a tag on #6, they probably dive very deep during the day and come up to shallower waters at night to feed.
This video shows a live megamouth swimming around (#37, by sharkman's accounting).
Our next shark has a few different names: Sleeper Shark, Greenland Shark, and Gurry Shark, to name a few. These remarkable fish live in polar waters year-round, and are very large, the largest recorded one growing to a length of 21 feet (although unconfirmed reports of 24-footers exist as well).
- Parasites called copepods often attach themselves to the eyes of Greenland Sharks. Some people think that their bioluminescence acts as a lure to attract prey for the shark in a somewhat symbiotic relationship.
- Greenland Sharks are scavengers; they will eat just about anything they find, but their favorite food is carrion. Pieces of giant squid and even a reindeer (antlers and all) have been found in their stomachs as well.
- Raw sushi made from this shark would kill you. Their flesh is toxic to humans unless it's properly cooked, by boiling with many changes of water, or by drying it or just letting it rot over a long time. Rotted shark meat is considered a delicacy in Iceland and Greenland.
Image from Shark-Pictures.com
Sometimes they're called Ghost Sharks, sometimes Elephant Sharks, but whatever you call them, these fish are very strange-looking. And I have a confession to make--they're not technically sharks. They are actually chimeras, which are cartilaginous fishes related to sharks and rays. Like sharks, the males have claspers for reproduction (although chimeras have more than sharks) and the females lay eggs in egg sacs like some sharks as well. However, they have smooth skin, without the rough denticles on sharks, and perhaps most interestingly, while sharks' upper jaws come away a bit from their skulls. Instead, their jaws are fully fused into their head, and their teeth are not as removable as sharks' are, but more like grinding tooth plates.
Scientists think that the Elephant Shark's "snout" is used to look for prey under the sand. They live off the coasts of Australia and New Zealand, and if you order fish and chips there, you might be eating an elephant shark-- they are a common commercial fish.
Image from the Florida Museum of Natural History Ichthyology Department.
I hope that you all enjoyed today's sharks. Tune in tomorrow as we will look at the ancestors of sharks and how they have (or have not) changed over millions of years.