Visualizing Environmental Science

286 CHAPTER 11 The Ocean and Fisheries

Fishermen tend to concentrate on
a few fish species with high commercial
value, such as menhaden, salmon, tuna,
and flounder, and other species, collectively
called bycatch, are unintentionally caught and
then discarded. Although bycatch is extremely
difficult to determine globally—it is defined
differently in different places, and statistics are often not
available—the FAO estimates that annual global bycatch
exceeds 7 million metric tons (7.7 million tons). Most of
these unwanted animals that are dumped back into the
ocean are dead or soon die because they are crushed by
the fishing gear or are out of the water too long. The

United States and other countries are trying

to significantly reduce the amount of bycatch

and develop uses for the bycatch that remains.

In response to harvesting, many nations

extended their limits of jurisdiction to 320 km

(200 mi) offshore. This action removed most

fisheries from international use because more

than 90 percent of the world’s fisheries are harvested in

relatively shallow waters close to land. This policy was

supposed to prevent overharvesting by allowing nations

to regulate the amounts of fishes and other seafood har-

vested from their waters. However, many countries also

have a policy of open management, in which all fishing

bycatch The fishes,

marine mammals, sea

turtles, seabirds, and

other animals caught

unintentionally in a

commercial fishing

catch.

WHAT A SCIENTIST SEES

Modern Commercial Fishing Methods

15,000

10,000

5,000

Cod (thousands of fish)

1980 1985 1990

Year

1995 2000 2005

Trawl

bag

Purse seine

net

Lines with hooks

Drift net

Long lines

Spotter airplane

Sonar

Satellite tracking

Aquaculture

Floats

Based on data by O’Brien, L N. Shepherd, and L. Col. Assessment
of the Georges Bank Atlantic Cod Stocks for 2005. Northwest
Fisheries Science Center Ref. Document 06-10 (June 2006).

a. The important cod fishery on Georges Bank, off
the coast of Massachusetts, has collapsed due to
overfishing. The U.S. Commerce Department closed
large portions of Georges Bank in 1994, but cod are
only slowly recovering.

b. Scientific evidence indicates that modern
methods of harvesting fish are so effective that
many fish species have become rare. Sea turtles,
dolphins, seals, whales, and other aquatic organisms
are accidentally caught and killed in addition to the
target fish. The depth of longlines is adjusted to
catch open-water fishes such as sharks and tuna or
bottom fishes such as cod and halibut. Purse seines
catch anchovies, herring, mackerel, tuna, and other
fishes that swim near the water’s surface. Trawls
catch cod, flounder, red snapper, scallops, shrimp,
and other fishes and shellfish that live on or near the
ocean floor. Drift nets catch salmon, tuna, and other
fishes that swim in ocean waters.