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Fishing methods
from the Ministry of Fisheries. New Zeland
Trawling
Seining (pron: “sayning”) involves dropping a net to surround
and trap a school of fish. There are two types of seining – Danish
seining, which is used to catch fish near the bottom of the sea,
and purse seining, which is used to catch fish near the surface.
Purse seining is shown below:
Hand-lines are mainly used by recreational fishers. A hand-line is a single fishing line,
usually attached to a rod, and held by hand.
Long-lines have a main fishing line, with lots of shorter lines hanging off it. The
shorter lines have bait and hooks attached to them. The main line is anchored at each
end, and floats stop the line from sinking. Long lining fishing :
Dredging - used to gather scallops and oysters from shallow water. A fishing
boat tows a steel net (dredge) along the sea floor, and the net scrapes up all
the shellfish living there.
Pots and traps - A pot-like trap that is attached to a long
rope is baited with fish and dropped from a fishing
boat. The rope is marked with floats so that the fisher
can easily find the line when they want to haul up the
pot again.
Gas exchange in fish
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The respiratory system of fishes are their gills
Gills supported by a piece of bone – gill bar
The gills have spaces between them – gill pouches
In bony fishes the opening is covered by a piece of
skin and bone – operculum
• Gill Lamellae – soft, thin flaps of tissue on the
outside of the gill bar…these have a large surface
area and are thin (so it has a good blood supply)
• Gill rakers – are on the other side of the gill bar to
prevent dirt from clogging the lamellae…can be used
for filter feeding
Fish Gill
Breathing movements
• Water flows in through the mouth over the
gills , out through the gill slits providing
oxygen dissolved in it
• Some swim fast with open mouths, some lie in
fast running water, ( facing upstream) some
make breathing movements.
Breathing movements
Fish Movements
Fishes have
• A flexible vertibral column – moves body from side to side
• A swim bladder – air filled sac just below the vertebral column
that is found in all bony fishes. Used to adjust the amount of
air in it to keep the fish afloat
• They are streamlined – limited friction so the move easily
through the water (scales overlap backwards, covered by a
thin, transparent skin which secretes mucus to reduce drag.
• Fins – help them to gain balance in the water
Various navigational equipment used
at sea
• Compasses – magnetic compasses are used to
determine direction relative to Earth’s magnetic
poles by using a pointer that is magnetized
• Sonar –uses sound to detect other vessels and
marine life and to navigate in the ocean
• Radar – uses electromagnetic waves (radio
waves) to detect objects that are moving or
stationary
• GPS – Global Positioning System uses satellites to
determine the position of other objects, of
weather , etc.
While at sea fishermen recreational or
commercial must have and use safety gear
Such as:
• Life jackets
• Life rafts
• Inflatable tubes
Most fishing is done with the fisherman above water
Sometimes some people go scuba diving. Although many people do not take safety
precautions or are careful during the diving process many hazards can occur.
Some hazards are:
• Higher pressure as the diver goes deeper that can cause respiratory problems
by damaging the membranes in the lungs
• The bends (known as Decompression sickness) – occurs when dissolved gases
coming out from a solution goes into bubbles in the body on depressurization.
Bubbles can go into any part of the body and thus this can have a variety of
symptoms including some that can lead to death
• Nitrogen narcosis – is reversible but is still dangerous as it causes as
temporary decline or loss of senses, movement and can have a feeling of
numbness. It is when nitrogen gas dissolves in the blood as depth during diving
increases.
• Embolism – when an obstruction occurs in a blood vessel such as a blood clot
or air bubble. Holding the breath on ascent is the main cause of an air embolism. As the
diver moves from high pressure at depth to a lower pressure at a shallower depth, the air
in the lungs expands. If this air doesn’t escape out the windpipe, the only release is via the
delicate air membranes in the lungs, called alveoli, and into the blood stream.