Page 167 - (DK) Ocean - The Definitive Visual Guide

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MIGRATORY SHOALS
Pelagic fish such as these mackerel
move around the ocean in response to
temperature changes. They are among
the pelagic zone’s larger predators.

Active Swimmers Pelagic Fisheries

The animals of the plankton, especially small crustaceans such as Continental shelf waters support
copepods and krill, are eaten by fish, mainly small, shoaling species massive quantities of pelagic
such as herring, sand eels, sardines, and anchovies. Most of these fish, ultimately sustained by
fish live permanently in midwater, using the seabed only to spawn abundant plankton. The most
or to avoid predators. They are strong swimmers (nekton), using important fisheries are for
speed to catch prey and evade predators. They can travel long herring, sardines, anchovies,
distances against residual currents to feed and also to reach their pilchards, mackerel, capelin and
spawning grounds. Small, shoaling fish are, in turn, food for larger jackfish. Squid are also fished
predators, such as squid, tuna, cetaceans, commercially. Many fish stocks are
NEKTONIC INVERTEBRATE and sharks. Whale sharks, basking under severe pressure as boats and
Squid are the only invertebrates sharks, and baleen whales are among nets get bigger and the technology to
that swim strongly enough to be
classed as nekton. They catch a the largest of the marine animals, yet pinpoint shoals becomes ever more
variety of prey including fish and they feed directly on plankton, sophisticated. Pelagic fish and squid
planktonic crustaceans. consuming vast quantities. are caught in drift nets that hang
about 30 ft (10 m) down from the FOOD CHAIN THREAT
surface. In the north Pacific, some 105,000 miles Sand eels are food for
(170,000 km) of drift net is available to major sea-birds (such as this Arctic
tern), seals, cetaceans, and OCEAN ENVIRONMENTS
fisheries; unfortunately, these nets also trap cetaceans,
larger fish. Despite their
turtles, and diving birds. Drifting longlines are used importance at the base of
for tuna and swordfish; these also catch juvenile fish, many food chains, vast
sharks, turtles, and seabirds. Midwater trawls capture quantities are taken by
vast quantities of shoaling fish such as herring, fisheries for feeding to
livestock and farmed fish, and
mackerel, and sardines. Small-scale fisheries for a
are burned as fuel oil.
wide variety of other pelagic species are important
in sustaining local coastal communities worldwide.