192 Sharks: The Animal Answer Guide
Are sharks affected by pollution?
As detailed in chapter 9 (“Is it safe to eat sharks?”), many pollutants
wind up in the food chain and become concentrated at high trophic levels.
Sharks are the top predators in many areas and eat prey animals already
contaminated by a wide array of pollutants. We know very little about the
direct effects of these pollutants on sharks, but given their effects on many
other animals, it is likely they will have similar negative impacts on shark
health, especially on large, long-lived species.
How are sharks affected by litter?
Because many sharks are scavengers, they tend to sample unlikely and
unnatural items that are discarded at sea. Fortunately, sharks are able to
regurgitate inedible items readily (see “What do sharks eat?” in chapter
7). One likely and unavoidable form of litter that has a known impact on
sharks consists of discarded or lost fishing nets, especially monofilament
gill nets. Sharks are often trapped in such nets when they blunder into
them or try to feed on dead and dying fishes caught in the net. Sharks then
twist and turn in an effort to escape these nets, thereby entangling them-
selves and losing the ability to move water over their gills, which leads to
drowning. Other trash such as plastic straps encircle sharks and dig into
their bodies. Monofilament fishing line wraps around the saws of sawfishes,
cutting into and disfiguring the saw.
How do people catch sharks?
In modern times, most deliberately caught sharks are captured with
baited hooks. Often, these lines—involving individual hooks or “long
lines” with thousands of baited hooks—are actually set for billfishes, tu-
nas, or other fishes; and the sharks are a bonus, or a nuisance. The sharks
caught this way are processed for their fins and meat or simply discarded
after their fins have been removed (see “What is finning?” below).
Some of the sharks that live near the bottom—the more abundant small
sharks and most skates and rays—are caught in large trawl nets dragged
along the bottom. The international fishery for Spiny Dogfish is one ex-
ample, with some “net hauls” capturing thousands of animals.
In many places, sharks have been caught for food using a variety of
traditional methods involving hooks made from bone or shell and vari-
ous noise-making devices that attract sharks to a baited hook or within
spearing distance. (See “What roles do sharks play in various cultures?” in
chapter 11.)
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