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global warming continues, it will
cause higher ocean temperatures,
sea ice will melt further, and wind
and ocean current patterns will
change. As a result, nutrients from
the upper ocean will be transferred
to the deep ocean, starving marine
ecosystems and reducing
photosynthesis by phytoplankton,
which serve as the base food in the
ocean food chain. Within three
centuries—by 2300—the world’s
fisheries could be 20 percent less
productive, and between 50 to 60
percent less productive in the North
Atlantic and western Pacific. The
predictions, calculated in 2018 by
scientists at the University of
California, Irvine, are based on
extreme global warming—a 17°F
(9.6°C) increase, but their models
show that it is a possibility.Finding new solutions
Seafood consumption has risen
from 21.8 lb (9.9 kg) per capitaTHE HUMAN FACTOR
annually in the 1960s to more than
44 lb (20 kg) in 2016. Global demand
is predicted to reach around 236
million tons by 2030. Aquaculture,
the farming of fish and seafood, has
begun to meet much of the demand
and has the potential to reduce the
pressures on wild fish stocks.
However, aquaculture has its own
problems. Nutrients and solids
added to the water can cause the
environment to degrade. The
buildup of organic matter from
many fish in a farm can change the
sediment chemistry, which has an
impact on the surrounding water.
Fish may escape, introducing alien
species or diseases into the outside
freshwater or marine environment.
While fish farming helps meet
demand, overfishing still poses
huge dangers for the health of the
world’s marine ecosystems, and the
economic future of many nations.
The Canadian moratorium severely
disrupted the economy and culture
of Newfoundland and neighboring
maritime provinces. To avoid such
crises, more governments will have
to develop sustainable fishing
practices, and protect the health
of ecosystems and fish stocks. ■Effects of pollution
Two main types of pollution
damage marine ecosystems.
Runoff from fertilizers is a
common problem: the nitrogen
and phosphorus that many
contain produce algal blooms
(overgrowths of algae, or
phytoplankton), which later
die. As they decompose, they
take up oxygen, creating a
“dead zone” in the water that
cannot sustain life. Because
fish must leave such water or
perish, juvenile fish living
close to the shore are at risk
before they move into the open
ocean. In 2017, the annual
dead zone in the Gulf of
Mexico was more than
8,500 sq miles (22,000 sq km).
Plastic pollution is another
threat because fish eat it and
get caught in nets and debris.
Estimates suggest there are
more than 5 trillion pieces of
plastic in the ocean, with
over 8 million tons added
each year. If plastic pollution
continues unchecked, the
volume of plastic in the
ocean will exceed that of
fish by 2050.Thick blooms of phytoplankton
appear in red on this satellite image
of the Gulf of Mexico. Bacteria break
down decaying algae, releasing CO 2
and absorbing essential oxygen.A deep-sea salmon farm, built in
China, begins its journey to Norway.
The huge, semi-submersible cylinder
aqua-farming platform is designed to
produce 1.5 million salmon a year.US_266-269_Overfishing.indd 269 12/11/18 7:47 PM