Longlines

              The bottom longline is the most common type of hook-and-line gear in Thailand.  It consists of a main line, branch lines (hook lines) and hooks.  The construction of bottom longline gear used in Thailand is the most common and general type of bottom longline gear.  The main line is usually made of vinylon, which is dyed with juice obtained form mangrove bark.  When polyethylene is used for the main line, sinkers are attached to it directly or to the joints between the main line and branch lines, in order to increase the sinking force.

              Polythylene is the main material for the branch lines, but nylon monofilament is also used quite frequently.  The interval between two adjacent branch lines is 2.0-2.5 m, when the target species are large-sized fish, such as red snapper, grouper and Spanish mackerel.  The length of branch lines for this type of gear is 40-60 cm.  When the target species are medium-sized fish, such as threadfin and marine cat-fish, the branch lines are spaced less widely, about 1.4-2.0 m apart, and the length of a branch line is about 50 cm.

              The bottom longline for ray is somewhat different from an ordinary bottom longline described above.  The branch lines in this gear are fastened close together, with intervals of only about 27-33 cm.  The branch lines are slightly shorter than the interval, 25-30 cm.  The catching mechanism of a bottom longline for ray is different from that of an ordinary longline gear.  In the latter case the fish to be caught is attracted by bait, where as the bottom longline for ray entangles and hooks the fish without bait.

              The hooks for ordinary bottom longline are all of nearly the same shape, but vary in size.  This type of hook has a long shank and a rounded bend.  The length of shank ranges from 2.0 cm to 5.5 cm.  All the hooks are barbed.  The hooks for the bottom longline for ray are shaped differently from the hooks used for the ordinary bottom longline.   They are long and angular, with a very sharp point but with no barb on it.  Hooks are dipped in soya bean oil after operation to protect them from rusting coconut oil is not used, because of strong smell.

              Hooks are arranged on a wooden or bamboo “hanger” which is called tap in Thai, meaning “a set”.  The length of a hanger for an ordinary bottom longline is 50-80 cm, which is sufficient to accommodate about 120-200 hooks.  The hanger for a longline for ray is about 120-135 cm long, and about 300 hooks are arranged on it.

              Bottom longline are usually operated early in the morning.  Shooting is done while removing hooks from the hanger which is stood up-right and attaching bait on one hook after another.  The number of hooks used for one operation depends on the size of the boat and the construction of gear, but an ordinary bottom longline has between 600 and 1500 hooks. In the case of the bottom longline for ray bait is not used. Therefore shooting is done as the hooks are removed from the hanger.  As the interval between two adjacent branch lines is very short, 3-5,000 hooks are used in an operation.

              Bait for an ordinary bottom longline is sardine or mackerel, whose body size is about 10 cm.  Fish are cut into halves, head and tail part, and used for baiting snapper, grouper, Spanish mackerel and other fish.  Squid is also good bait for longline, but it is not used widely, because the price of squid is sometimes quite high.  In some cases, for example when fishing for the fourfinger threadfin, live bait is used.  This is usually small mullet, about 7-8 cm long.

              With an ordinary bottom longline, hauling of line the gear starts immediately after the shooting is finished.  The bottom longline for ray is kept on the bottom for two hours or more before hauling.  There is no facility for hauling line aboard ship.  Hauling is done entirely by hand.