284 CHAPTER 11 The Ocean and Fisheries
- Contrast fishing and aquaculture and relate the
environmental challenges of each activity. - Identify the human activities that contribute to
marine pollution and describe their effects. - Explain how global climate change could
potentially alter the ocean conveyor belt.
T
he ocean is so vast, it’s hard to imagine that
human activities could harm it. Such is the
case, however. Fisheries and aquaculture,
marine shipping, marine pollution, coastal
development, offshore mining, and global climate change
all contribute to the degradation of marine environments.
Scientists estimate that in 2008, less than 4 percent of the
ocean remained unaffected by human activities, and 41
percent had experienced serious harm (Figure 11.11a).
Marine Pollution and
Deteriorating Habitat
One of the great paradoxes of human civilization is that
the same ocean that provides food to a hungry world is
used as a dumping ground. Coastal and marine ecosys-
tems receive pollution from land, from rivers emptying
into the ocean, and from atmospheric contaminants
that enter the ocean via precipitation. Offshore mining
and oil drilling pollute the neritic province with oil and
other contaminants. Pollution increasingly threatens the
world’s fisheries. Events such as accidental oil spills—such
as the devastating Deepwater Horizon oil spill in the Gulf
of Mexico in 2010—and the deliberate dumping of lit-
ter pollute the water. The World Resources Institute es-
timates that about 80 percent of global ocean pollution
comes from human activities on land. In 2003 the Pew
Oceans Commission, composed of scientists, economists,
fishermen, and other experts, verified the seriousness of
ocean problems in a series of studies. Some of their find-
ings are shown in Figure 11.11b.
World Fisheries
The ocean contains valuable food resources. About 90 per-
cent of the world’s total marine catch is fishes, with clams,
oysters, squid, octopus, and other molluscs representing
6 percent of the total catch. Crustaceans, including lob-
sters, shrimp, and crabs, make up about 3 percent, and
marine algae constitute the remaining 1 percent.
Fleets of deep-sea fishing vessels obtain most of
the world’s marine harvest. Numerous fishes are also
captured in shallow coastal waters and inland waters.
According to the U.N. Food and Agriculture Organiza-
tion (FAO), the world annual fish harvest increased sub-
stantially, from 19 million tons in 1950 to a high of nearly
95 million tons in 2000, and 90 million tons in 2011, the
latest year for which data are available.Problems and Challenges for the Fishing
Industry No nation lays legal claim to the open ocean.
Consequently, resources in the ocean are more susceptible
to overuse and degradation than land resources, which in-
dividual nations own and for which they feel responsible.
The most serious problem for marine fisheries is that
many species have been harvested to the point that their
numbers are severely depleted. This generally causes a fish-
ery to become unusable for commercial or sport fishermen,
as well as for the other marine species that rely on it as part
of the food web. Large predatory fish such as tuna, marlin,
and swordfish have declined by 90 percent since the 1950s,
according to Canadian researchers who analyzed data from
ocean and coastal regions around the world. Scientists have
found that dramatically depleted fish populations recover
only slowly. Some show no real increase in population size
up to 15 years after the fishery has collapsed (see Figure a
in What a Scientist Sees).
According to the FAO, approximately 87 percent of
the world’s fish stocks are considered depleted, fully ex-
ploited, or overexploited. The three areas with the larg-
est number of depleted fish stocks are the northeastern
and northwestern Atlantic Ocean and the Mediterra-
nean Sea (see chapter opener). Fisheries have experi-
enced such pressure for two reasons. First, the growing
human population requires protein in its diets, leading
to a greater demand for fish. Second, technological
advances allow us to fish so efficiently that every single
fish is often removed from an area (see Figure b in What
a Scientist Sees).Human Impacts on the Ocean
LEARNING OBJECTIVES