Some Things about Sharks

This post is dedicated to my favorite actor, the late Robert Shaw.  Recently, after re watching one of his shark movies, I got the urge to learn more about sharks to then share that information with my Resplendent Readers.

For some information on Robert Shaw:
http://www.imdb.com/name/nm0001727/

Viewing  "The Deep" causes most people to remark that Jacqueline Bisset has pretty breasts.  Yes, the wet tee shirt scene made that clear.  Some people observe that Louis Gossett played a great villain.  Indeed, he had that malignant charm that a bad guy needs to keep you gleefully rooting against him.  What too many people fail to appreciate is Robert Shaw.  (The man had sparkling blue eyes of a sublime twinkle and hue second only to those of my husband, The Handsome One). 

In "The Deep" the Nick Nolte character had all sorts of diving accessories like an underwater camera and rubber shorts.  The Robert Shaw character simply strapped a scuba tank on over his street clothes and jumped into the ocean.  That is the sort of no nonsense manliness that gets my attention.  Of course, that's what's fun about having a favorite actor.  He tends to do things that please you.

So when are we going to talk about sharks, you ask? 

Right now.

Fossils belonging to sharks have been found,  believed to be 400 million years old, including a skeleton, skin and muscles.  These fossils suggest sharks haven't changed much.  Lots of fossil shark teeth have been found that look very much like the teeth of sharks living today.

Some Shark Facts

- they cannot swim backwards

- shark skin is smooth when rubbed from front to back, aerodynamically good, like the hull of a sail boat

- shark skin rubbed from back to front is rough.  Smaller fish use shark skin as an emery to remove  their own external parasites

- there are about 400 shark species identified so far

- sharks can identify the direction a smell is coming from by moving its head from side to side.  (Much as mammals do with hearing)

- the mako shark can reach speeds of 46 mph

- most sharks can see in color

- shark teeth vary from little nubs to big serrated triangles depending on what food the species eats

- some foods that sharks eat:  microscopic plankton, fish, whale carcasses, seals, dolphins, albatrosses,
sea turtles, stingrays, squid, crabs, sea urchins

- how they find food:  chasing prey, ambush, scavenging, filter feeding

- the average shark eats roughly the equivalent of  his own weight per month

- the age of a shark can be estimated by counting the growth rings in its spinal column

- sharks are slow growing.  Generally, the longer lived the shark, the later in life it matures.  Lifespans vary from 20-150 years/maturity achieved from 4-35 years.

Sharks are fish.  There are not, however, bony fish like a perch or tuna.  The shark is a cartilginous fish with a skeleton made of cartilage (a tough, flexible material also found in human joints, such as elbows and knees).  Other cartilginous fish:  rays and chimaeras.  Cartilginous fishes account for less than 5% of all fishes.

Bony fishes have bony skeletons and scales on their skin.  The shark's skin is also made up of scales but the scales are of harder stuff: tooth-like dermal deticle.  This skin protects the shark much like armour chain-mail.

Shark Sense

hearing- acute, they are able to detect sound from several miles away

smell- more like taste, really.  The shark has special receptor cells in the nostrils that act like taste buds to identify stuff in the water that flows over the receptor cells

vision- eyeballs much like most vertebrates.  Sharks are able to see fairly well, especially in low light thanks to a mirror-like layer in each eye that boosts the available light by reflecting it back onto light sensitive cells in the eye

taste- taste buds are located in the throat and the lining of the mouth.  The shark takes a bite of something, if it is deemed palatable, he swallows it. (Ideal foods are ones with a thick layer of high- energy fat, like a seal.  Even an obese human isn't really worthwhile.  This is why sharks usually spit people out after they bite them)

electroreception- the ability to detect electricity generated by other living things.  A shark can sense an animal that is not moving and buried under the ocean bottom by only its breathing and heart beat





Shark Sex

Most sharks are loners so migration is usually necessary for mating to occur.  Not a great deal is known about shark romance.  What is known, in some species, a female shark, when ready to mate will emit a hormonal substance into the water.  Males from miles around descend upon her.  Demonstrations of masculine vigor follow, including fighting and bloodshed.  The female chooses her suitor.  Typically, her choice is the largest and most dominant male.

The male shark has two external reproductive organs known as claspers.  (When not in use they are rolled up like a window shade and tucked in, in keeping with good aerodynamics). 

Some species lay eggs, others, live birth.  Gestation varies among species.  The closest sharks come to child rearing is giving birth in a sheltered lagoon rather than in open sea.


see some cool shark pictures:

http://animals.nationalgeographic.com/animals/sharks/

sources:
Sharks by Mark Carwardine
The Shark Almanac by Thomas B. Allen