Environmental Engineering Reference
In-Depth Information
and London contain dangerously high levels of toxic
mercury. Consumption of high levels of mercury is es-
pecially dangerous for pregnant women, fetuses, and
infants feeding on breast milk.
Sharks are also killed for their livers, meat (chiefly
mako and thresher), hides (a source of exotic, high-
quality leather), and jaws (especially great whites,
whose jaws can sell for as much as $10,000). Some are
killed simply because we fear them. Sharks (especially
blue, mako, and oceanic whitetip) also die when they
are trapped in nets or lines deployed to catch sword-
fish, tuna, shrimp, and other commercially important
species.
Despite our unkind treatment of them, sharks
save human lives. They are teaching us how to fight
cancer, which sharks almost never get. Scientists are
also studying their highly effective immune system,
which allows wounds to heal without becoming
infected.
Sharks are especially vulnerable to overfishing be-
cause they grow slowly, mature late, and have only a
few young each generation. Today, they are among the
most vulnerable and least protected animals on earth.
In 2003, experts at the National Aquarium in
Baltimore, Maryland, estimated that populations of
some shark species have decreased by 90% since 1992.
Eight of the world's shark species are considered criti-
cally endangered or endangered and 82 species are
threatened with extinction.
In response to a public outcry over depletion of
some species, the United States and several other
countries have banned hunting sharks for their fins in
their territorial waters. Unfortunately, such bans are
difficult to enforce.
With more than 400 million years of evolution be-
hind them, sharks have had a long time to get things
right. Preserving their genetic development begins
with the knowledge that sharks may not need us, but
we and other species need them.
Case Study: Why Are Sharks
Important Species?
Some shark species eat and remove sick and
injured ocean animals. Some can help us learn
how to fight cancer and immune system
disorders.
The world's 370 shark species vary widely in size. The
smallest is the dwarf dog shark, about the size of a
large goldfish. The largest is the whale shark, the
world's largest fish. It can grow to 15 meters (50 feet)
long and weigh as much as two full-grown African
elephants.
Various shark species, feeding at the top of food
webs, cull injured and sick animals from the ocean,
thus playing an important ecological role. Without
their services, the oceans would be teeming with dead
and dying fish.
Many people—influenced by movies (such as
Jaws
), popular novels, and widespread media cover-
age of a fairly small number of shark attacks per
year—think of sharks as people-eating monsters. In
reality, the three largest species—the whale shark,
basking shark, and megamouth shark—are gentle gi-
ants. They swim through the water with their mouths
open, filtering out and swallowing huge quantities of
plankton
(small free-floating sea creatures).
Every year, members of a few species—mostly
great white, bull, tiger, gray reef, lemon, hammer-
head, shortfin mako, and blue sharks—injure 60-100
people worldwide. Between 1990 and 2003, sharks
killed a total of 8 people off U.S. coasts and 88 people
worldwide—an average of 7 people per year. Most at-
tacks involve great white sharks, which feed on sea
lions and other marine mammals and sometimes mis-
take divers and surfers for their usual prey. Whose
fault is this?
Media coverage of shark attacks greatly distorts
the danger from sharks. You are 30 times more likely to
be killed by lightning than by a shark each year—and
your chance of being killed by lightning is already ex-
tremely small.
For every shark that injures a person, we kill at
least 1 million sharks, or a total of about 100 million
sharks each year. Sharks are caught mostly for their
fins and then thrown back alive into the water to bleed
to death or drown because they can no longer swim.
Shark fins are widely used in Asia as a soup ingre-
dient and as a pharmaceutical cure-all. In high-end
restaurants in China, a bowl of shark fin soup can cost
as much as $100. As affluence—and demand for this
delicacy—increases among the Chinese middle class, a
single large fin from a whale shark may become worth
more than $10,000.
According to a 2001 study by Wild Aid, shark fins
sold in restaurants throughout Asia and in Chinese
communities in cities such as New York, San Francisco,
x
H
OW
W
OULD
Y
OU
V
OTE
?
Do we have an ethical obliga-
tion to protect shark species from premature extinction and
treat them humanely? Cast your vote online http://biology
.brookscole.com/miller11.
Foundation Species: Other Major Players
Foundation species create and enhance habitats that
can benefit other species in a community.
Some ecologists think the keystone species should be
expanded to include
foundation species,
which play a
major role in shaping communities by creating and
enhancing their habitats in ways that benefit other
species. For example, elephants push over, break, or
uproot trees, creating forest openings in the savanna
grasslands and woodlands of Africa. Their work pro-
motes the growth of grasses and other forage plants
