Apple #482: Sharks

I've been sick this week.  No energy for much else besides sleeping and lying on the couch.

So now, for no particular reason, I give you sharks.


The Great White Shark, or more simply, the white shark. Here's what Jacques-Yves Cousteau reported when he encountered one: "Shark saw us, its reaction was unexpected. Frightened, it released a cloud of excreta and disappeared with incredible speed." Basically, the shark crapped its pants at the sight of a human and ran.
(Photo from Daily Scuba Diving)


SHARK ATTACKS
or You've Got More Fish to Fry Closer to Home

Movies like Jaws -- which I will stop and watch any time it's on TV, by the way. "Smile, you son of a" -- and cable TV shows like When Sharks Attack! have inflated people's fears of sharks.  In real life, most of us have very little reason to fear sharks compared to all the other life-threatening things out there.  Here are some facts to put sharks in perspective:

(If you want the details, click the Read More link)

• About 100 people in the world are bitten by sharks each year. Of these, five to ten die.

• The chance of being killed by a shark is one in 300 million. 

• The chance of being killed by airplane parts falling from the sky is one in 10 million.

• You are more likely to be struck by lightning than you are to be attacked and killed by a shark.

• You are more likely to be killed by a tornado than you are to be attacked by a shark.

• You are more likely to be killed by an alligator than you are to be killed by a shark.

• Pigs kill more people every year than sharks do.

• Dogs kill more people every year than sharks do:

Year	Number of Dog Attack Fatalities	Number of Shark Attack Fatalities
2001	23	3
2002	15	0
2003	25	1
2004	22	2
2005	28	1
2006	31	0
2007	31	0
2008	23	1
2009	32	0
Total	230	8

Source: International Shark Attack File

• You are far more likely to injure and kill yourself performing any number of home improvement projects than you are to be attacked and killed by a shark.

• If you want to worry about something, worry about heart attacks, not shark attacks.  Heart disease is the number one killer in the United States, leagues ahead of sharks.

• Up to 100 million sharks are killed by people every year.

OK, you get the point.  Enough of the depressing stuff.


SHARK FACTS
or, Did you know this about sharks?

Now that we've got the whole fear situation out of the way, we can take in some facts about these animals.

• The jaws of larger sharks are about twice as powerful as the jaws of a lion.

• Some sharks are scared off by scuba divers' bubbles.

• Sharks swim with their mouths open not to look threatening, but because this is how they breathe. That's right, sharks are a bunch of mouth-breathers.

A Great White, swimming with his mouth open so he can breathe. I think he looks kind of like a doofus.
(This photo was actually used in conjunction with another to perpetrate a Photoshop hoax. Read about it at Hoax Slayer)

• They have to keep their mouths open to keep water flowing into and through their gills.  The gills then extract the oxygen from the water. 

• They can stop swimming, but not for very long.  They have to keep that water flowing through their gills.  Some sharks find currents and rest there with their mouths open, allowing the current to push the water across their gills. 

• Still other sharks -- like the nurse shark -- have spiracles which keep the water moving and allow the sharks to rest.

• Sharks do sleep, but they keep their eyes open. Only one side of the brain sleeps at a time so that they are able to keep breathing as they rest.

• There are all sorts of myths that say sharks can smell one drop of blood up to a mile away, or one drop of blood in the entire ocean, or across some such enormous distance like that.  Exaggerations!

• They are extremely good at smelling, though. Some of the larger sharks can smell evidence of their prey in the water at one part per billion, which is one drop in an Olympic-sized swimming pool.  That's hardly at entire ocean; more like a block or two in the neighborhood.

• Sharks also have an additional sensory system called the ampullae of Lorenzini.  They are tiny pores -- holes, really -- along the shark's nose and mouth. They look kind of like blackheads.

Ampullae of Lorenzini sprinkled all across the underside of this shark's nose. Looks almost like the shark could use some blackhead remover, doesn't it?
(Photo from MalcT32)


Cross-section of the ampullae of Lorenzini. Each hole, or ampulla, is filled with gel or jelly that aids the shark in detecting all sorts of things about their surroundings.
(Diagram from Seaworld)

• These little holes are filled with a kind of gel which works like an electroreceptor. The gel detects electrical impulses in the water.  Since all animals produce electrical impulses (yes, you and I do too), and the gel in these ampullae help the sharks detect animals moving near them in the water.

• The detection only works up to a few inches or a foot away, so it's believed to help the sharks stay with their prey in the final closing moments before capture, not to hunt down the fish over long periods of time. Still, those blackheads are pretty handy.

• They may also help the shark determine temperature changes of the water and water pressure, which could come in useful during mating season or in determining whether they're in good fishing waters in general.

• If you've been to an aquarium, you may have had the chance to touch a shark in the water. The aquarium people will tell you, only touch the shark from nose to tail, not the other way around. This is because they don't want you to cut your fingers on the rough barbs on the shark's skin.

This little boy is touching a nurse shark in a touch pool at the Santa Barbara Museum of Natural History.

• These barbs are called dermal denticles, literally, toothed skin. They provide the shark with an almost chain-mail like protection.  One biologist with a fondness of engineering notes, "dermal denticles are about as hard as granite and as strong as steel."

• The toughness of their skin may be one of the reasons why sharks have been able to survive on this planet as long as they have. Sharks have lived here on earth for 400 million years. That makes them older than the dinosaurs. And older than us.

• Once upon a time (in human history), because of its roughness and durability, shark skin was used for all sorts of purposes: 
• as sandpaper
• as grips on the handles of swords
• after removing the denticles, as leather to make shoes, belts, and drum heads.

• If you've eaten rock salmon, rock eel, huss, or flake, you've eaten shark.  For some reason, people don't like to eat fish if it's called "shark," so fish markets and chefs change the name to something people find more palatable.

• Most of the fish sold in British fish & chip shops are from spiny dogfish, which is actually a kind of shark.

Dogfish sharks -- so named because they travel and hunt in packs -- are typically grouped so close together, they are easy to catch in large numbers. Thus they become fish & chips.
(Photo from New Brunswick.net)

• Some sharks -- the Great White, the Mako, and the Thresher -- are warm blooded.

• After mating, some female sharks can retain the male’s sperm in their bodies for use when she is ready to reproduce, even if that does not happen until next season.

• Depending on the species, young sharks -- called pups -- may be born from an egg that hatches outside the mother, or develop within an egg inside the mother until it's ready to hatch, or born alive from the mother.

SPECIFIC SPECIES
or Here are a couple types of sharks you might not know about 

• There are somewhere between 300 and 350 species of sharks.

• The largest shark, the whale shark, is generally considered harmless to humans. Some scuba divers have even reported whale sharks allowing them to hitch rides by hanging onto their fins.

Whale sharks are easily identified by their spotted skin. They can grow up to 60 feet long.
(Photo from the Discovery Channel)

• The teeth of a whale shark are about the size of a match head. This is because they eat more like whales than like sharks -- by filtering plankton into their mouths.

The fish in front of this whale shark's mouth aren't worried because the shark isn't after them; it's after the plankton.
(Photo by Jana P on TravelBlog)

• Whale shark skin can be up to 10 cm thick, which makes it the thickest skin in the world. 

Well, surely you've seen photos of the hammerhead shark before.
(Photo from Metro.co.uk)

• You can't tell from this photo, but the hammerhead's eyes are at the outer ends of the "hammer" part of its head. 

• Scientists suspect that the reason for the hammer is to allow the greatest number of ampullae of Lorenzini across this shark's face -- in other words, to enable this shark to be that much better at finding food.

• Hammerheads were added to the Endangered Species list in 2008 because of overfishing in China and Hong Kong.

This tiger shark lives off the coast of Hawaii. Be careful around these dudes.
(Photo from Hawaii Shark Encounter Tours)

• Tiger sharks are named for the spots along their flanks.

• They'll eat pretty much anything they can fit into their mouths.  Sea turtles, rays, squid, dolphins, birds, garbage, all kinds of stuff. They'll even eat jellyfish.

• Not only will they eat just about anything, they're fast swimmers, they're curious, and they're aggressive. Fortunately, they tend to stay away from humans for the most part, but if you see a tiger shark in the water, give it a lot of respect and a very wide berth.

Oceanic whitetip, with its telltale long floppy-looking fin.
(Photo from Torpedo Tours)

• Oceanic whitetips have, as the name suggests, white patches on the tips of their fins. 

• Even more distinctive, though, is the extra-long, rounded pectoral fins. They look like they're way too big for the shark's body. The dorsal fin -- the one that sticks up out of the water -- is rounded, too.

• They eat barracuda and tuna -- those two fish seem like polar opposites -- as well as many other types of fish and sea animals.

• Lantern sharks, or velvet belly sharks, are bioluminescent, which means they have little cells along their bodies that glow in the dark.

• I couldn't find any decent pictures of lantern sharks that weren't copyrighted, so if you want to see what one looks like, check out SeaPics.

• Great White Sharks -- the kind portrayed in Jaws and other attack movies -- have a pretty big predator that they fear: Orcas.  Also known as killer whales, orcas are at the top of the food chain in the ocean. They hunt in packs and sharks are some of their favorite foods.  They are faster and stronger than even the biggest Great Whites. 

• Funny, we go to Seaworld to see orcas -- incredibly fierce hunters -- jump around for our entertainment, but we scream and run at the sight of a shark fin.

Sources
University of Florida, International Shark Attack File Best resource for shark info anywhere!
Shark Facts.org
sharks-world.com 
Canadian Shark Research Laboratory, Ampullae of Lorenzini
Erik V. Thuesen, Ph.D., Evergreen State College, Ampullae of Lorenzini
The Naked Science Forum, Sharks Smell Blood from a Mile Away! debunked
Reef Quest Centre for Shark Research, Biology of Sharks and Rays, Skin of the Teeth
MarineBio, Great Hammerhead Shark