May 15th, 2010 
molitva leyli Longline Fishing for Giant Tuna : BluefinTuna, Big Eye Tuna & Swordfish
The longline used for tuna fishing is made up of units (sometimes known as “baskets“), each of which consists of a main horizontal line about 250 to 800 m long with 4 to 15 branch-lines, each with a wire leader and a hook. The depth where the hooks are set in the water column is a crucial element, this depth in which the longline is settled can be regulated mainly by modifying the intervals of the main line between float lines and partially by adjusting the length of float-line and/or the speed of shooting, to a lesser extent, by modifying the length of the branch-lines.
longline basket set for Large pelagic; tuna, swordfish ; main line, branch, hook, swivel,singker, nylon monoline, wire leader, look, snap, snape with swivel, vinil spring
Longline Vessel Overview
Industrial tuna longliners are usually large vessel with length ranging between 30 and 70 m. The basic requirements of a tuna longliner, industrial type, are: adequate speed to reach far away fishing grounds, enough autonomy (fuel, water, accommodation of crew, etc.), capacity for operating in the high sea (sometimes very rough seas at cold temperature), facility for very efficient freezing storage (to attain extremely cold temperature under 45°C) to keep the highly valued tuna for months together, suitable deck arrangement and equipment, protection of crew from rough weather and sea conditions, machineries for shooting and hauling up longlines quickly and proper storage facilities for keeping the fishing gears and accessories. These large specialised vessels can stay away from their home ports for 10-24 months.
Mustad coastal longline vessel deck arrangement
Japan longline vessel
Longline Fishery Production Systems
Possible exploitation forms using tuna longlining are: industrial and semi-industrial.
Longline Handling Mode
If the vessel’s cruise is less than a month, the tuna can, in principle, be stocked directly in isolated fish hold. However, nowadays the large commercial tuna longline vessels use to stay at sea for months (sometimes up to almost a whole year). In such situation, the catch has to be frozen (in perfect conditions for maintaining top quality for the product). Hence it is necessary to extract blood, pre-cool, freeze and install fish in a store at a temperature of -40°C to -60°C. It is very essential to freeze the fish meat to such a low temperature so as to retain the quality and colour of the meat for a very long period.
Longline Fishing Environment
Tuna longlining is carried out in open waters including in the high sea. The hooks fish in sub-surface areas and at depths of about 100 to 300 meters (maximum depths of 175 m for the conventional longlines and of 300 m for the deep longlines).
depth setting for large pelagic target longline fishingmore than 100 m depth
A 48-hour Pacific bluefin tuna sequence of depth in metres (scale on the left), light level (no scale) and water temperature in degrees C (scale on right) from a recovered external PAT tag, image from www.stuff.co.nz/
A 48-hour southern bluefin tuna sequence of depth in metres (scale on the left), light level (no scale), water temperature and gut (internal) temperature in degrees C (scale on right) from a recovered archival tag implanted in the gut cavity.
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