Diet and Eating Habits
Food preferences and resources
As a group, sharks and batoids eat almost anything: fishes,
crustaceans, molluscs, marine mammals, and other sharks.
While some sharks are probably not very selective feeders,
certain sharks eat some foods more than others. For example,
hammerhead sharks (Sphyrna spp.) are known for eating stingrays;
Bull sharks (Carcharhinus leucas) eat other sharks; and
smooth dogfish (Mustelus spp.) eat crabs and lobsters.
Tiger sharks have been called "garbage cans of the
sea" because they feed opportunistically on both live food
and carrion. Prey includes bony fishes, other sharks, marine
mammals, seabirds, and invertebrates. Tiger sharks are
ecologically important predators of sea turtles and sea snakes.
Many sharks prey most often on the weak, inferior members
of a population. They select weak, ill, injured, or dying prey
because it is easier to catch.
Food intake
In a zoological environment, a shark eats about 1% to 10% of
its total body weight per week. Studies on sharks in the wild
show similar food intake.
Methods of collecting and eating food
The characteristic teeth of each species are adapted to
that particular species' diet. The teeth may be serrated or
smooth. Most are used for seizing prey, cutting, or crushing. For
sharks, plate-like triangular teeth are the most common shape.
Because of the biting force exerted by sharks, teeth often
break off while sharks are feeding. They are replaced by teeth in
reserve rows. The Lemon shark (Negaprion brevlrostris) can
replace a tooth in about eight days.
Most predatory species of sharks seize, grasp, and tear
food. A shark may circle its prospective prey and may even bump
it with its snout or pectoral fins. A shark's jaws are loosely connected
to the rest of the
skull at two points. As the upper jaw extends forward from the
mouth, teeth of the lower jaw first encounter prey. The lower jaw
teeth puncture and hold prey. The upper jaw teeth slice. A
shark's short jaws make the bite powerful.
Many species of sharks and most rays are adapted for bottom
feeding. Bottom feeders use the upper jaw to help pick up prey
items. One example of a bottom feeder, the horn shark has two
types of teeth. Front teeth are pointed for grasping and back
teeth are flat and molarlike for crushing. Stingrays (family
Dasyatidae) and eagle rays (family Myliobatidae) have teeth that
are fused into plates.
Another mechanism some sharks and batoids use for
collecting food is filter feeding. Rays in the family Mobulidae
(Manta spp., for example), the Basking shark (Cetorhinus
maximus), and the megamouth shark strain enormous quantities
of plankton from the water on gill rakers. Whale sharks als
filter feed, but instead of using gill rakers, they strain
plankton through a spongy tissue supported by cartilaginous rods
between the gill arches. Filter feeders have reduced,
nonfunctional teeth.
Some elasmobranchs are quite specialized for feeding.
A Thresher shark (Alopias spp.) uses the long upper
lobe of its tail to corral schools of fish.
A
sawfish (Pristis pectinate) moves its head from side to
side and strikes prey with its long rostrum.
Nurse sharks (family Ginglymostomatidae) use their
thick lips to create suction, effectively pulling their
prey from holes and crevices.
A Cookiecutter shark (Isistius spp.) uses suction to
attach itself to whales and large fishes; it carves out a
core of flesh with its large triangular teeth.
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