Introducing Sharks, Skates, Rays, and Chimaeras 21
Why are sharks important?
Sharks are important because of the roles they play in ecological sys-
tems. In all habitats, on land and in the water, the natural food web has
multiple levels and connections, beginning with the plants that produce
food from the sun, up to the predators that feed on plant-eating animals,
the predators that feed on other predators, and the scavengers that feed on
decomposing remains. Sharks occupy the top levels of food webs in all of
the world’s oceans. Such top-level carnivores keep the numbers of other
species in check, preventing both starvation and overuse of resources.
When top level carnivores are eliminated from a system, their absence
leads to both overpopulation and depopulation at other levels because the
impacts cascade down through the food web.
Predators also remove diseased, injured, or poorly adapted individuals
from prey populations. This predatory behavior is a part of natural selec-
tion, constantly improving the genetic make-up of prey populations and
even potentially reducing the likelihood that diseases will spread. Sharks
also scavenge on the remains of dead animals, recycling the energy and
nutrients that are locked up in decomposing bodies. Sharks in their roles
as both predators and scavengers are essential to the health of marine eco-
systems.
Why should people care about sharks?
Humanity depends on healthy ecological systems for food, clothing,
medicines, building materials, clean water, and mental well-being. When
fished at sustainable levels, sharks provide protein for people who might
otherwise have a protein-deficient diet. Drugs made from sharks and based
on the chemistry of sharks have been used to treat human bone diseases and
cancer (see “Are any medicines made from sharks?” in chapter 8). When
sharks are overfished and ecological systems are thrown out of balance, the
direct and indirect usefulness of sharks to humans and other organisms is
lost.
But it is not only the practical use of resources that affects our well-
being. Many studies have shown that people get genuine pleasure from
experiencing nature, especially wild animals in their natural surroundings.
We have a deep-seated affinity for and curiosity about the natural world,
in no small part because it has been evolutionarily advantageous to under-
stand the living world around us. Our ancestors who learned about and un-
derstood nature were more likely to pass on their genes than early humans
who were less informed. Ecotourism, the popular practice of traveling to