Transcript File
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 • • • • 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.