Introduction to Sharks

• Species

• There are over 360 species of sharks
• They can range in size from small enough to fit in your hand to up to 65 feet

• Smallest Shark is the Pygmy Shark
• Largest Shark is the Whale Shark

• Filter feeder, feeds on plankton

• Whale shark

• How does an almost 50 ft shark survive on plankton?
• By eating a LOT of it

• Shark skeletons

• Sharks are cartilaginous fish

• their skeletons are made of cartilage

• Cartilage is more advantageous to bone because

• It’s lighter than bone
• It’s less dense

• This means that sharks

• Are more agile than bony fish
• Are fast so they can hunt well

• Shark respiration

• Sharks have uncovered gills used for respiration
• The gills extract oxygen as water passes over them
• Spiracles:

• Special slits above the eyes that allow sharks to respire while not in motion.

• A small percentage of sharks need to stay in constant motion to respire

• Shark teeth

• attached to soft tissue (NOT jaws)
• range from needlelike to large flat teeth
• used for holding on and shredding into prey (NOT chewing!)
• Sharks have multiple rows of teeth that are replaced often
• They can have about 25,000 to 30,000 teeth in one lifetime

• some replace teeth every 8-10 days
• others every few months

• Life span

• Lifespan varies by species
• Most live about 20 – 30 years
• It is thought that the whale shark can live over 100 years

• Sense of smell

• Incredible sense of smell
• They can detect amounts of blood as small as 1 ppm (part per million)
• Rely on sense of smell to locate prey

• Locating prey

• Lateral lines

• Sense organ used to detect motion or vibrations in the water

• Electro-receptors

• Allow sharks to sense minute electricity caused by muscles and nerves in prey

• Eyes

• Sharks have eyelids but do not blink
• Water surrounding eye cleans it
• Have a membrane over eye that protects when being attacked or when hunting
• Great White Sharks roll eyes back when attacking

• Do sharks sleep?

• Scientists unsure
• Possible they sleep in a similar manner to dolphins
• Half the brain sleeps at a time

• Shark attacks

• 2010 - 79 attacks, 6 fatalities
• 2015 - 98 attacks, 6 fatalities (largest on record)
• 2017 - 82 attacks, 5 fatalities
• Majority occur in the United States
• More people die from lightning strikes and dog attacks each year

• Sharks involved in attacks

• Three types of sharks have been involved in a significant amount of attacks

• Great White
• Tiger Shark
• Bull Shark

• Great White Shark

• Great Whites are generally about 13-16 ft long and weigh 1500 - 2450 lbs
• Found in waters between 54 oF and 75 oF
• Countershading

• White underside and gray dorsal side
• Difficult to see when looking at horizontally
• When seen from above, gray blends in with the water
• When seen from below, white blends in with surface of water

• Typical prey

• Sting rays, tuna, smaller sharks, dolphins, seals, sea lions
• Shark attacks most often occur in the morning, within 2 hours after sunrise
• Hard to see a shark close to the bottom
• Attack from below at fast speeds

• Tiger sharks

• Average 11 feet and 850 - 2000 lbs
• Commonly found around islands in the central Pacific
• Dark spots and stripes are prominent in young sharks and fade as the shark matures
• Hunting habits

• Teeth can bite through bone and turtle shells
• Known to circle its prey and even study it by prodding it with its snout
• Tiger sharks devour their entire prey when attacking

• Hawaii

• Tiger sharks have become a problem in Hawaii
• Hunted to help control attacks, but no decrease occurred
• Considered sacred by native Hawaiians

• Bull shark

• Dwell in shallow water, possibly posing highest threat to humans
• Can tolerate freshwater
• Size

• Males: 6.8 ft, about 200 lbs
• Females: 11.5 ft, about 700 lbs

• Hunting habits

• Bump and Bite Technique
• Shark circles prey often bumping them before the actual attack.
• They are extremely territorial and will attack other animals that enter their territory.

• Hammerhead shark

• Habitat: Shallow tropical and warm temperature waters
• Diet: Stingrays, other small sharks, fish, crustaceans
• Size: 12 - 20 ft.
• Attacks: 18 (0 fatal)
• Hammerheads have small mouths and seem to do a lot of bottom-hunting. (Stingrays!)
• Their wide-set eyes give them a better visual range than most other sharks.
• Hammerheads are also known to form schools during the day, sometimes in groups of over 100

• Why do sharks attack people?

• Mistaken Identity

• Shark mistakes a person in the water as a seal when looking from below the waters surface
• Provoked by sailors
• Curiosity

• Sharks typically bite once and then swim away

• Explanations:

• Humans do not taste like their typical prey
• Return to the prey after it exhausts itself

• Dolphin protection

• Sharks will not attack when dolphins are around
• Scientists unsure why this phenomenon occurs

• Avoiding an attack

• Avoid water during darkness or twilight hours
• Do not enter water if bleeding from an open wound
• Do not wear shiny jewelry – resembles fish scales
• Avoid areas near commercial fishing
• Avoid murky waters
• Do not splash a lot

• Fending off an attack

• Hit back in sensitive areas such as the eyes and gills
• Shows shark you are not defenseless