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HABITAT
Reef sharks are usually found on coral reefs and in nearby
tropical waters. A typical site is a shallow, sandy lagoon with scattered coral
formations, bounded by an area of built-up coral known as a "reef flat." On the
seaward side, the reef flat falls away steeply into deep waters, which are linked to the
lagoon by channels that form the reef sharks' access routes.
Gray reef sharks generally frequent the deep waters of
the outer reef slope, but they often congregate in the channels and use them to enter the
lagoon. The small black-tip reef shark can swim in shallower water. It hunts over the reef
flat at high tide, with its dorsal fin cutting the surface.
The slightly bigger white-tip shark prefers deep gullies
and caves, while the large silver-tip shark usually stays on the outer reef slope. Largest
of all is the tiger shark, which slips into the channels from the outer fringes to pick
off large fish-- including other sharks.
Above: Reef sharks give birth to
live young that are perfect miniatures of their parents.
Reef sharks
belong to the family Carcharbinidae, which contains approximately 60 species. Most of
these species inhabit coral reefs in tropical waters. They are able to coexist by
exploiting different types of prey on separate parts of the coral reef Reef sharks vary
widely, from the small, fish-eating black-tip shark to the huge, fearsome tiger shark--
which has been known to kill humans.
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Moving stealthily through
tropical coral reefs, reef sharks are highly efficient killers. These creatures have
little to fear except larger predators of their own kind and the ever-present threat of
humans.
BREEDING
Reef sharks breed in summer. After following a female's scent
trail through water, the male grips her body or fin with his teeth, usually wounding her
despite her thick skin. He then inserts one of two elongated clospers (sexual
organs) into her cloaca (genital opening). The clasper acts as a guide for the sperm,
which is passed into a special sac within the female and stored for several months before
fertilizing her eggs the following spring.
Like infant mammals, the unborn sharks are connected to the
mother's bloodstream by an umbilical cord and placenta. This enables them to absorb
nutrients during the 8- to 12-month gestation period. Unlike other fish, whose offspring
are born from eggs that hatch in water, the female shark gives birth to relatively few
well-formed, live young.
Above: Small fish called remoras
sometimes "hitch a ride" on reef sharks. The remoras use suckerlike disks on
their heads to attach themselves to the reef sharks.
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FOOD & FEEDING
Reef sharks are opportunistic feeders that eat just
about anything, from shellfish to sea lions. The black-tip reef shark feeds on crabs,
lobsters, cuttlefish, and small reef fish. It hunts primarily at night in an area that is
familiar, ambushing its prey among coral heads in the reef shallows. Although the
white-tip reef shark also hunts at night for similar prey, it forages in different waters,
taking bottom-dwelling fish and octopuses from the reefs caves and crevices. The larger,
stronger gray reef shark hunts for bigger prey in deep water by night and day. The
silver-tip hunts similar prey at similar depths, which may partly explain why the gray
reef shark is so aggressively territorial.
The gray reef shark warns intruders by
twisting its body, raising its snout, and dropping its pectoral fins. It finally attacks
with slashing bites that are not part of its normal feeding method. It can even drive off
the 16-foot tiger shark, which can kill a gray reef shark and then swallow it whole.
KEY FACTS
Length: Varies, from 5 ft. in the
black-tip reef shark to 16 ft. in the tiger shark.
Habit: Active predators by day and night.
Diet: Mainly fish, crustaceans, cuttlefish, and
octopuses.
Sexual maturity: Approximately 2 years, depending
on growth rate and size.
Breeding season: Summer.
Gestation: 8-12 months, depending on species.
Number of young: About 14; fully formed when
born. |
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| Did You Know?
Reef sharks are highly developed at birth. One infant bit a
scientist as he removed it from the dying mother's womb.
Although reef sharks are dangerous, they can be surprisingly tame.
Several have been trained to take fish from divers without biting them.
Although reef sharks are regarded as voracious feeders, they can
actually go for days without eating. The sharks convert energy so efficiently that they
can get by on relatively little food.
Reef sharks locate prey by detecting tiny electrical signals that
are generated by their victim's nervous system. |
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