General Shark Info

Shark Dermal Denticles

Are modified scales that cover a shark's body. Though very small, less than 1 millimeter in size, but still play important roles. They serve for protection & streamlining of the animal.

If you rub you hand across it one way, it feels very smooth, but rubbing against the grain and it feels rough like sandpaper (a fact I can attest to from my experiences with bonnetheads & exotic aquarium sharks). It's not hard to believe shark skin was actually once utilized as sandpaper!

Denticle structure: 1) Pulp 2) Dentine 3) Enamel-like vitrodentine 4) Bony basal plate (or root)

Shark demal denticles (much larger than actual size)

Shark Teeth

Just look at modern sharks, they have hundreds of teeth! One of the secrets of their success are owning "tooth factories", in which when a tooth becomes too worn or broken, a replacement tooth right behind it is ready to take over. It is estimated sharks can go through 10,000 to 50,000 teeth (seated in 5-15 rows) in their lifetime! Shark teeth are designed to fit the function they serve. Some are built for crushing, slicing, grinding, and/or piercing so it makes sense they come in a wide range of shapes & sizes, even within one species in several cases. It is almost hard to believe shark teeth are just very modified dermal denticles.

Shark Tooth Replacement Rates

Whaler/Carcharhinus sharks: Within 1st year, teeth replaced about every 8-15 days. In adults of this group, likely every tooth replaced in a month.

Basic Tooth Types

1) Large, triangular, sharp and may have serrations (For shearing)

2) Narrow, curved, length moderate to long (for seizing small fast prey)

3) Smooth or arranged in pavement formation (for crushing hard prey)

Shark Tooth Type "1" left (juvenile meg tooth), Shark Tooth Type "2" Right (C. hastalis posterior)

Shark Tooth Type "3" (Port jackson shark lower jaw, not mine)

Shark Teeth Functions

-Easier Feeding

-Defense against predators

-Grasping females while mating

Known Body weight consumption rates/ day:

Shortfin Mako: ~3 %

Young lemon sharks: ~1.7%

Pelagic sharks (i.e. sandbar & blue): 0.2-0.6%

Nurse sharks: 0.2-0.3%

Buoyancy

All fish must have a way to regulate their buoyancy or else they'll simply sink (if denser than water) or float (lighter than water, not the case usually). Bony fish do this via their gas-filled swim bladder, but sharks & rays lack this. They make up for it with a very large, oily liver (up to 25% total body weight & can help sharks survive without food for weeks), and having a light-weight cartilaginous skeleton.

Shark Coloration

Usually:

Dorsal (Top)

-Grey

-Brown

-Or blue (open ocean sharks)

Bull shark

Blue shark

Ventral (underside)

-Pale or white

This color scheme, called counter-shading, helps sharks to camouflage and appear nearly invisible from the sides as sunlight strikes the shark.

Basic body types

-Long & slender (e.g. benthis catsharks, cookie cutter sharks)

-Large & conico-cylindrical (e.g. fast pelagic Lamniforms)

-Strongly flattened (e.g. benthic angelsharks)

Angel shark

Extra Senses

Chemoreception

Mechanoreception

Photoreception

Electroreception

Sensing prey

1 km (750 feet) away: Olfaction (smelling blood/oil)

750 feet- 75 feet: Movement detection & hearing

-Lateral line system (consisting of sensory hair cell receptors) & sensitive ears to detect movement

75 feet & closer: Eye vision

-At least some sharks have color vision

-More active sharks have larger eyes

-Carcharhiniforms have a 3rd eyelid, aka the nicatating membrane, to protect eyes while feeding.

(Other sharks, such as the great white, rolls their eyes toward their head for protection while feeding)

Reproduction

-Slow growth rate (compared to most fish/ etc. animals)

-Reach sexual maturity in about 2-20 years

-May mate every 2-3 years & have one (i.e. sand tiger sharks) or many pups (tiger sharks can have up to 80, whale sharks up to 300)

-Usually born in shallow "Nursery areas" away from hungry optimistic adult sharks

-Average gestation: 9-12 months

Reproductive Methods (in no particular order)

1) Oviparous: Lay horn-like egg cases (examples: Zebra shark, the catsharks, swellshark, the necklace carpetshark, some Epaulette sharks, and the Hornshark)

2) Aplacental viviparous: Live young nourished in uterus via yolk sac (examples: Great white sharks, sawsharks, Mako, crocodile sharks, Cookiecutter sharks, Pelagic thresher, Greenland shark, Gummy shark, Soupfin shark, Pacific Angelshark, Pygmy sharks, Nurse shark, Tiger shark, and Sand tiger sharks)

3) Placental viviparous: Live young nourished in uterus by placenta formed from modified yolk sac attached to uterine wall (example: majority of living Carcharhiniformes)

Etc. Life Cycle

-Seem to live on average 20-30 years (~70 years in Piked dogfish, greenland sharks can live hundreds of years)

Etc. Facts

-Sharks can smell small amounts of blood up to 1 kilometer (750 feet) away

-Some sharks decide palatability of potential food items while in their mouth (why most shark attacks on humans don't result in serious injury)

-For most species, females grow larger & reach sexual maturity later than males

-Species with very wide geographical distribution: Common thresher, shortfin mako, basking shark, blue shark, oceanic whitetip, scalloped hammerhead, blacktip, piked dogfish, bull shark & tiger sharks

-Mutalistic relationship with Pilot fish & Remoras ( such fish get to eat sharks' parasites while shark benefits from losing parasites & following fish ride the shark's "wave" for easier navigation)

-Many (or most?) have a larger brain than most vertebrates relative to body length (needed for complex sensory systems)

-Have a mouth that is ventral (under their head) rather than terminal (at end of head, i.e. most bony fish & ancient sharks such as Cladoselache) maybe due to primitive sharks being benthic (feeding on the ocean floor)

-Have a "J" or "U" shaped stomach

-Sharks may be able to swallow a prey item up to 40% its own size (great whites known to have swallowed whole sea turtles, men in armor, tuna, seals, barracuda, smaller sharks, & even 150 dungeness crabs!)

-Able to exert their stomach (turn it inside out to get rid of indigestible objects, common in oceanic whitetip, silky & dusky sharks, less common in great whites, bull sharks, shortfin makos, & smooth hammerheads)

-Water must continually flow across these slits in order for the shark to breathe. This can be accomplished by the shark's swimming, by standing still in a current, or by fanning water across the gills with its fins (done by nurse sharks).

-Largest shark jaws by body proportion: Angel sharks

-Largest shark teeth by body proportion: Cookiecutter sharks

sources:

-http://www.fossilguy.com/gallery/vert/fish-shark/index.htm

-Shark perfect predator (Alessandro de Maddalena book)

http://www.enchantedlearning.com/subjects/sharks/anatomy/Gills.shtml

http://www.enchantedlearning.com/subjects/sharks/anatomy/Repro.shtml

Fishes of the Open Ocean book by Julian Pepperell (countershading fact)