Page 458 - Environment: The Science Behind the Stories

Trawling entails dragging immense cone-shaped nets
through the water, with weights at the bottom and floats
at the top. Trawling in open water captures pelagic fish,
whereas bottom-trawling (Figure 16.20c) involves drag-
ging weighted nets across the floor of the continental shelf
to catch groundfish and other benthic organisms, such as
scallops.

Fishing practices kill nontarget animals
and damage ecosystems

Unfortunately, these fishing practices catch more than just
the species they target. Bycatch, the accidental capture of
animals, accounts for the deaths of millions of fish, sharks,
(a) Driftnetting marine mammals, and birds each year. The impact of bycatch
can be substantial. A 2011 report from NOAA reported that
17% of all commercially-harvested fish were captured unin-
tentionally.
Driftnetting captures dolphins, seals, and sea turtles, as
well as countless nontarget fish. Most of these creatures end
up drowning (mammals and turtles need to surface in order
to breathe) or dying from air exposure on deck (fish suffocat-
ing when kept out of the water). Driftnetting is now banned
in international waters because of excessive bycatch, but the
practice continues in most national waters.
Similar bycatch problems exist with longline fishing,
which kills turtles, sharks, and albatrosses, magnificent sea-
birds with wingspans up to 3.6 m (12 ft). Several methods
are being developed to limit bycatch from longline fishing
(such as using flagging to scare birds away from the lines),
(b) Longlining but an estimated 300,000 seabirds of various species die
each year when they become caught on hooks while trying
to ingest bait.
The scale of bycatch and solutions to address it are illus-
trated by the story of dolphins and tuna. Several species of
dolphins that associate with yellowfin tuna become caught in
purse seines set for the tuna in the tropical Pacific. In purse
seining, boats surround schools of tuna with a net and draw
the net in, trapping both tuna and dolphins. Hundreds of
thousands of dolphins were being needlessly killed each year
throughout the 1960s. The U.S. Marine Mammal Protection
Act of 1972 forced U.S. fleets to try to free dolphins from
seines before they were hauled up and spurred fishing gear CHAPTER 16 • M AR in E A nd Co A s TA l s ys TEM s A nd R E sou R CE s
to be modified to allow dolphins to escape. Bycatch dropped
greatly as a result (Figure 16.21a).
However, as other nations’ ships began catching tuna,
(c) Bottom-trawling dolphin bycatch rose again. Because U.S. fleets were oper-
ating under more restrictions, the U.S. government required
Figure 16.20 Commercial fishing fleets use several meth- that tuna imported from foreign fleets also minimize dolphin
ods of capture. In driftnetting (a), long transparent nylon nets bycatch, and it supported ecolabeling efforts (p. 173) to label
are set out to drift through open water to capture schools of fish. tuna as “dolphin-safe” if its capture used methods designed to
In longlining (b), lines with numerous baited hooks are set out in avoid bycatch. These measures helped reduce dolphin deaths
open water. In bottom-trawling (c), weighted nets are dragged from 133,000 in 1986 to less than 2000 per year since 1998.
along the floor of the continental shelf. All methods result in
large amounts of bycatch, the capture of nontarget animals. The We can celebrate this success story but should also recognize
illustrations above are schematic for clarity and do not portray the that there is little accountability for the many “dolphin-safe”
immense scale that these technologies can attain; for instance, labels, that sharks and other animals continue to be caught
industrial trawling nets can be large enough to engulf multiple as bycatch, and that dolphin populations have not recovered
Boeing 747 jumbo jets. (Figure 16.21b). 457

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