marine fisheries

2. Pelagic fish, by definition, are found near the ocean surface or
in middle depths.
As a result, pelagic fisheries must search larger volumes than
demersal fisheries. However, most pelagic fish species exhibit
behaviours that increase their catchability.
The most import characteristic is shoaling, in which individuals
of the same species form and travel in aggregations.
Several pelagic species also exhibit clear patterns of vertical
migration, often staying deep in the water column, or near
bottom, by day but migrating to surface waters at dusk.
In some cases fishers have used techniques such as artificial
light sources to enhance shoaling behaviour and improve
fishing.

3. The marine pelagic environment is the largest aquatic
habitat on Earth, occupying 1,370 million cubic
kilometres (330 million cubic miles), and is the habitat
for 11% of known fish species.
The oceans have a mean depth of 4000 metres. About
98% of the total water volume is below 100 metres
(330 ft), and 75% is below 1,000 metres (3,300 ft).

4. Marine pelagic fish can be divided into-
1.Pelagic coastal fish and
2.Oceanic pelagic fish.
Coastal fish inhabit the relatively shallow and sunlit
waters above the continental shelf, while
Oceanic fish (which may well also swim inshore)
inhabit the vast and deep waters beyond the
continental shelf.

5. Pelagic fish range in size from Small coastal forage fis,
such as herrings and sardines, to
Large apex predator oceanic fishes, such as bluefin tuna
and oceanic sharks.
They are usually agile swimmers with streamlined
bodies, capable of sustained cruising on long-
distance migrations.
Many pelagic fish swim in schools weighing hundreds of
tonnes. Others are solitary, like the large ocean
sunfish weighing over 500 kilograms, which sometimes
drift passively with ocean currents, eating jellyfish.

6. Small pelagic fish are usually forage fish that are hunted
by larger pelagic fish and other predators. Forage
fish filter feed on plankton and are usually less than 10
centimetres long. They often stay together
in schools and may migrate large distances between
spawning grounds and feeding grounds. They are found
particularly in upwelling regions around the northeast
Atlantic, off the coast of Japan, and off the west coasts
of Africa and the Americas. Forage fish are generally
short-lived, and their stocks fluctuate markedly over the
years.

7. Medium size pelagic fishes include
Trevally, barracuda, flying fish, bonito, mahi mahi and coastal
mackerel.
Many of these fish hunt forage fish, but are in turn hunted by yet
larger pelagic fish. Nearly all fish are predator fish to some measure,
and apart from the top predators, the distinction between predator
fish and prey or forage fish is somewhat artificial.
Many large pelagic fish are oceanic nomadic species which
undertake long offshore migrations. They feed on small pelagic
forage fish, as well as medium-sized pelagic fish. At times, they
follow their schooling prey, and many species form schools
themselves.
Examples of larger pelagic fish are
tuna, billfish, king mackerel and sharks and large rays.

8. Marine pelagic fish species may be broken down
into five subcategories based on the depth of water
a species most commonly inhabits.
These layers of water, in order of increasing depth,
include
1.Epipelagic
2.Mesopelagic
3.Bathypelagic,
4.Abyssopelagic and
5.Hadopelagic zones.

9. SCIENTIFIC CLASSIFICATION
KINGDOM- ANIMALIA
PHYLUM- CHORDATA
CLASS- ACTINOPTERYGII
ORDER- SCROMBIFORMES
FAMILY- SCROMBIDAE
SUBFAMILY- SCROMBINAE

10. A tuna is a saltwater fish that belongs to
the tribe Thunnini, a sub-grouping of the mackerel
family (Scombridae).
Thunnini comprises fifteen species across
five genera, the sizes of which vary greatly, ranging
from the bullet tuna (max. length: 50 cm (1.6 ft),
weight: 1.8 kg (4 lb)) up to the Atlantic bluefin
tuna (max. length: 4.6 m (15 ft), weight: 684 kg
(1,508 lb).
The bluefin averages 2 m (6.6 ft), and is believed to
live for up to 50 years.

11. Herring are forage fish, mostly belonging to the
family Clupeidae.
Herring often move in large schools around fishing banks and
near the coast.
The most abundant and commercially important species belong
to the genus Clupea, found particularly in shallow, temperate
waters of the North Pacific and the North Atlantic Oceans,
including the Baltic Sea, as well as off the west coast of South
America. Three species of Clupea are recognised, and provide
about 90% of all herrings captured in fisheries. Most abundant
of all is the Atlantic herring, providing over half of all herring
capture. Fishes called herring are also found in the Arabian
Sea, Indian Ocean, and Bay of Bengal.