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Sharks have swum in the ocean over 400 million years…
How do sharks maintain
neutral buoyancy?

Sharks have several adaptations that can aid their ability to
         be neutrally buoyant (neither float nor sink).
   1. Lack true bone  cartilaginous skeletons  much
2. Have large livers full of low-density oils  provide some
 3. Lack swim bladder BUT some species, like sand tiger
    (Carcharias taurus), gulp air into stomachs  provide
                      additional buoyancy.
                    Shark Diversity
                      The two largest
                       shark species -
                         basking and
                       whale sharks -
                      are slow-moving
                        filter feeders,
                        live off tiniest
                            fish and

Whale shark teeth
How many kinds of fins do
sharks have?
How many kinds of fins do
sharks have?

 Sharks have five different types of fins:
        pectoral, pelvic, dorsal,
            anal, & caudal.

   These fins are rigid, supported by
     cartilaginous rods (NOT bone).
How many kinds of fins do
sharks have?
             pectoral fins:
 - paired
 - ventrally near anterior (front) end of
 - used primarily for lift as shark swims
How many kinds of fins do
sharks have?

             pelvic fins:
  - paired
  - behind pectoral fins
  - used for stabilization while shark
 How many kinds of fins do
 sharks have?

                  dorsal fin:
 - commonly appears as shark skims
  along water's surface.
- may have one or two dorsal fins
   - stabilize shark during swimming
How many kinds of fins do
sharks have?
                anal fin
- main function is stability (for sharks
  that have one)
- ventral (bottom) side between pelvic
  and caudal fins.
 How many kinds of fins do
 sharks have?
                            caudal fin
- also called tail fin
- upper half and lower half of shark‘s tail not equal in size 
  upper portion usually larger
   - especially pronounced in thresher shark (below)  has upper tail
     lobe longer than shark's body.
- responsible for propelling shark through water as it swims.
Do sharks lay eggs or give
live birth?

  • Sharks exhibit great diversity in
    reproductive modes.
    – oviparous (egg-laying)
    – viviparous (live-bearing)
How do sharks reproduce?

• All sharks have internal fertilization 
  sexual reproduction

 Mating has been observed in relatively few
 species of sharks, but both hormonal and
 behavioral cues are likely involved.
   How do sharks reproduce?
Development of the embryo proceeds according to
      the mode of reproduction and embryonic
          nutrition of the particular species.
• In oviparous species, eggs are laid.
• In viviparous species, gestation takes place in

Sharks are hatched or born as juveniles, or smaller
   versions of the adult. There is no larval stage.
Do sharks lay eggs or give
live birth?

         Bonnethead shark and litter (NOAA)
What is a mermaid's purse?

egg cases of many
   sharks, skates

Tough, protective
 purse-shaped egg
 case contains one
   fertilized egg.   Mermaid's purses from a clearnose
                     skate (Raja eglanteria) on top and a
                     chain dogfish (Scyliorhinus retifer)
                     on bottom
What is the correct term for a
baby shark?

    A baby shark is referred to as a pup.
Most sharks live only in marine
  environment in full-strength         Can sharks
Some coastal shark species can
                                       live in
  survive in brackish estuaries with   freshwater?
  mixed fresh- and saltwater. Many
  juvenile sharks use these brackish
  areas as nursery grounds.
Two shark species capable of
  surviving in freshwater for any
  length of time.
  - bull shark (Carcharhinus leucas)
  - speartooth shark (Glyphis sp.)
No populations live in completely
  landlocked freshwater lakes;
  always have route connecting to
Can sharks live in freshwater?
Bull sharks have
  been captured
  ~2,100 miles
  (3,480 km) up
  the Amazon
  River, and
  ~1,700 miles
  (2,800 km) up
  the Mississippi
  River (in Illinois
Can sharks live in freshwater?

The speartooth shark has been captured over ~60
 miles (100 km) up the Adelaide River in Australia.
Do sharks have tongues?
     Sharks have a tongue referred to as a "basihyal".

 The basihyal is a small, thick piece of cartilage located on
       the floor of the mouth of sharks and other fishes.
It appears to be useless for most sharks with the exception
    of the cookiecutter shark. The cookiecutter shark uses
     the basihyal to rip chunks of flesh out of their prey.

Taste is sensed by taste buds located on the papillae lining
   the mouth and throat of the shark. The taste receptors
   help the shark decide if the prey item is suitable or not
                 prior to ingesting the item.
Are sharks warm or cold

     Most sharks, like most fishes, are
 cold-blooded, or "ectothermic." Their body
  temperatures match the temperature of
          the water around them.
However, there are 5 species of sharks that
        have some warm-blooded, or
         "endothermic" capabilities.
 Are sharks warm or cold
Lamnidae family: known as mackerel sharks,
  –   white (Carcharodon carcharias)
  –   shortfin mako (Isurus oxyrinchus)
  –   longfin mako (Isurus paucus)
  –   porbeagle (Lamna nasus)
  –   salmon (Lamna ditropis)
• unique ability to elevate internal body temps above
  surrounding environment - use highly-developed
  network of blood vessels that retain heat produced
  by muscles.
Are sharks warm or cold
White shark - able to elevate stomach temperature
   as much as 57ºF (14ºC) above ambient water
Are sharks warm or cold
  Salmon shark -
possibly most warm
   blooded shark,
   maintains body
 temp around 77ºF
(25ºC), elevation of
  over 70ºF (21ºC)
above temp of sub-
arctic waters where
       it lives.
What is a nictitating
membrane?          nictitating membrane -
                        thin, tough membrane
                       or inner eyelid in eye of
                         many shark species;
                         covers eye to protect
                             from damage,
                        especially just prior to
                          feeding where prey
                          may inflict damage
                        while trying to protect
  How do sharks detect prey?
Sharks have many keen
       senses that are
        mostly geared
  towards helping them
         locate prey.
     Depending on the
        species or the
   environment certain
    senses are more or
      less important to
 them for locating their
   targeted prey, which
     is most often fish.
 How do sharks detect prey?

Sharks use five senses: smell (chemoreception),
   vision, hearing, the lateral line system, and
 electroreception (ampullae of Lorenzini, above)
                for capturing prey.
 How do sharks detect prey?

lateral line system: all fishes possess; allows to
      detect waves of pressure or mechanical
                disturbances in water.
How do sharks detect prey?
           lateral line - a series of tubes
               located just below skin’s
             surface, running lengthwise
                on both sides of shark's
                body, from head to tail.
            When moving water, sound,
             vibration, pressure changes
                stimulate sensory cells,
             shark is alerted to potential
                prey in nearby waters.
How do sharks detect prey?
   Ampullae of Lorenzini -
   receptors that can detect
       weak electric fields.
Unique to sharks and their
   relatives. Primarily use to
 locate hidden prey, such as
    stingrays buried in sand,
which can not be detected by
 other senses. The stingray,
  like all living animals, emit
weak electric fields produced
 by muscular contractions in
             the body.
The white shark, when
targeting seals in coastal   Hunting Habits:
 areas, is thought to be
 primarily visual ambush     3 species: visual
        predator.                     ambush
                                   great white
Cruises on or near ocean
   bottom looking up to    (Carcharodon   carcharias)
   surface for basking or
  swimming seals. When
   prey is spotted, shark
   will make high speed
     rush from below,
  attempting to mortally
 wound it w/ first strike.
Believed most white shark attacks on surfers are
  result of shark mistaking surfboard for a seal.
  In most cases, once shark gets mouthful of
  fiberglass or neoprene instead of fatty seal, it
  will tend to leave scene. This initial strike can
  leave a victim with serious wounds.
Tiger sharks are usually
 nomadic in movements;       Hunting Habits:
use "long-range" senses,     3 species:
  like smell and hearing,
    for help to key in on    smell/hearing
            prey.            tiger
                             (Galeocerdo cuvier)
Detect scent of dead fish,
   birds, or turtles from
   very long distances,
  follow odor corridor to
Once close enough, vision becomes more
 dominant sense leading up to prey
 consumption. Of course, chance visual
 encounters with live prey often occur as
Hunting Habits:
                        Bull sharks tend to occur in
3 species:                  shallow coastal waters
random                     where visibility is often
bull                                 poor.
(Carcharhinus leucas)
                          Have smaller eyes than
                             other closely-related
                           sharks, so believed bull
                            sharks do not rely on
                           vision as much as some
                                of other senses.
When relying more on sense of hearing,
 smell, or lateral line, can more easily
 mistake human activity in water as that of
 prey (mostly schooling fishes).
Why are sharks called "apex
Apex predators:
• at top of food chain, have few or no
  natural predators
• keep populations of prey animals in check
   important in maintaining ecological
  balance of its environment.
Why do hammerhead sharks
have broad heads?
Hammerheads get common names from large
  hammer-shaped head (cephalophoil)
Cephalophoil - broad and flattened with eyes
  located on the outer edges of and nostrils also
  spread far apart.
Why do hammerhead sharks
have broad heads?
              structural advantages:
              • maximize lateral
                 search area
              • better able to track
                 scent trails with
                 increased distance
                 between nostrils
              • may provide
                 additional lift and
                 maneuverability as
                 shark swims
Why do hammerhead sharks
have broad heads? Hammerheads have:
                     • larger musculature
                         in the head region
                     •   wider range of
                         head movement

                     This allows:
                     • increased
                     • quicker
                       maneuverability at
                       high speeds
  Why do basking sharks swim
  with their mouths open?
 Usually seen swimming with
   mouth wide open, taking in
    continuous flow of water.
• Food strained from water by
  1000-1300 gill rakers
  located in gill slits  can
  strain up to 2000 tons of
  water per hour.
• Occasionally closes mouth
  to swallow prey.
• Feed along areas containing
  high densities of large
   – small crustaceans
   – invertebrate larvae
   – fish eggs and larvae
Are all sharks dangerous to
Of over 375 different species of sharks identified, only ~ 30
           have been reported to attack humans.
    Of these, only about a dozen should be considered
                    particularly dangerous.

         most unprovoked attacks on humans by:
           • white (Carcharodon carcharias)
               • tiger (Galeocerdo cuvier)
              • bull (Carcharhinus leucas)

All sharks, large and small, could be capable of inflicting
    wounds if provoked. They should all be treated with
                respect when encountered.
How many people are attacked
each year by sharks?

    50-70 shark attacks/year worldwide
Number of attacks increasing over decades:
• increased human populations
• use of oceans for recreational activity

As long as humans continue to enter sharks'
 environment – oceans - there will be shark
What are the different types of
shark attacks??
Provoked attacks - caused by humans touching/
  bothering sharks. Often involves unhooking
  sharks or removing them from fishing nets.
  However, recently there have been number of
  incidents involving divers attacked after
  grabbing or feeding shark while underwater.

Unprovoked attacks happen when sharks make
 first contact. (3 forms)
Unprovoked attacks:

1. Hit-and-Run Attacks - near beaches,
  where sharks hunt fish. In pounding surf,
  strong currents, murky water  shark may
  mistake movements of humans, usually at
  surface, for those of normal food, fish. Shark
  makes one grab, lets go, immediately leaves
  area. Legs/feet often bitten; injuries usually
  minor, deaths rarely occur.
2. Sneak Attacks - take place in deeper
  waters. Victim doesn't see shark before
  attack, us. from below. Result can be
  serious injury/death, especially if shark
  continues attack.
3. Bump-and-Bite Attacks - shark circles
  and actually bumps victim with its head or
  body before biting. As in sneak attack,
  shark may attack repeatedly, causing
  serious injury/death.
What is the practice of finning?
               In most commercial fisheries:
               • shark meat low value
               • fins valuable in Asian shark fin
                   soup market (> $700-1000/kilo)
               •   fishermen cut fins off sharks,
                   throw bodies overboard
               •   allows keeping expensive fins,
                   saving room to land/cargo more
                   marketable fish
               •   Oftentimes, sharks finned,
                   returned to sea still alive  drown
                   or starve
                   – Analogous to cutting legs off pet
                     dog and putting it back in the
What is the practice of finning?
                     While body of shark
                       is worth almost
                       nothing, shark fins
                       sell for $700-
                       1000/ kg
                     (70 times value of
                       kg of tuna)

                     Fins dried and sold
                        for shark fin soup
                        - traditional
                        Chinese dish
                        which sells for
                        $100+ bowl.
should we

Sharks are vital component of oceans and feed on wide variety
      of fish, shellfish, & mammals. Oceans remain healthy
  because every organism is part of complex food web. When
     any component of web is removed, balance in system is
     altered. Sharks are involved in several steps of this web
   including feeding on sick/dying and on larger animals such
       as whales, seals, & tuna, which have few predators.
What impact will it have on the
marine wildlife if the number
of sharks keep declining in the
long run?
Sharks are apex predators, the top of the food chain.
     If one removes species from any trophic level,
  there will be trickle-down effect. Since food web is
  very complex, predicting exactly what might occur
   is almost impossible. Safe to say with loss of an
       apex predator, there will be noticeable and
         oftentimes major negative ramifications.
The Future…

With sharks at the top of the ocean’s food
 chain, the annual slaughter of 100 million
  sharks (according to the United Nation's
     Food and Agriculture Organization)
     has a severe detrimental effect on
       the entire marine ecosystem.
 The survival of one of the ocean’s oldest
    and most beautiful animals is at risk.

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