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Longlining is a type of commercial fishing, in use since
the 19th Century.
It is classified as a passive fishing technique, making use
of lines with baited hooks, and is used to catch a number
of fish species including, tuna, shark, swordfish and cod.

A longline consists of a main line to which many
branchlines, or
snoods, are attached.
Each snood has a baited hook at its end.
Depending on the type of longline, buoys and weights
are attached to ensure that the longline is at its required

The number of hooks and lines depends on the size of
vessel, the degree of mechanisation and the size of the

The vessels used for longlining can range from small
open boats, using manually operated longlines, to large
ocean-going vessels, which are highly mechanized
and specialised and usually engage in single species

The main characteristics of a longline vessel that distinguish it from other fishing vessels are the rail roller, the longline hauler and in particular, the setting chute on traditional longline vessels, or the baiting and gear handling system on mechanised longliners.

The wheelhouse can be situated aft or forward, but on larger vessels the bridge is generally placed aft.
In typical arrangements the gear is hauled from the bow or from the side with a mechanical or hydraulic line hauler and the lines are set over the stern.

Small-scale longliners may haul by hand into baskets or tubs, or by using a hand cranked line drum.
On larger vessels, automatic or semi-automatic systems are installed to bait the hooks and to shoot and haul the lines.
Line storage on larger vessels normally incorporates a line drum, as the lines may be as long as100 km.
In general, such systems consist of rail roller, dehooker and hook cleaner, line hauler, hook separator, storage rack or drum.

Longlines can be used on the seabed, in midwater or just below the surface.
The length of longlines can range from a few hundred metres in coastal fisheries, to more than
100 km in large-scale mechanized fisheries, to which thousands of hooks can be attached.

Bottom Set Longlines

Bottom set longlines consist of a main line and snoods with baited hooks at regular intervals.
The number of hooks, the distance of snoods on the mainline, and length of the snoods depends on the target species, the handling capacity and technology used.

Courtesy Smolowitz - Figs a & b Bottom longlines © Drawing by Robin Amaral

They are set
on or near the seabed, and can be used on very rough seabeds and on coral reefs.

The importance of fish finding equipment is relatively low in bottom longlining.
Echo sounders are mainly used to record the water depth and provide information about bottom substrate and configurations.

Drifting Longlines

A drifting longline consists of a mainline kept
near the surface, or at a certain depth, by means of regularly spaced floats.
It has relatively long snoods with baited hooks, evenly spaced on the mainline, and may be of considerable length.
Some drifting longlines are set vertically, each line hanging from a float at the surface.

They are usually set from the stern of a vessel. At the end of each unit (basket) a buoy with a flag or lamp is set for marking purposes. With the help of the buoy line the fishing depth can be regulated.
The hooks are baited and the branch lines are fixed on the main line, in general, during setting. When the whole line has been set the gear is left drifting for some time.

Midwater Longlines

Midwater longliners are generally medium sized vessels
and operate worldwide. They are purpose built to catch
large pelagics such as shark, tuna and swordfish.

They must have reliable and relatively powerful engines,
be capable of withstanding the rigours of fishing
operations in distant waters for long periods of time,
have suitable machinery to shoot and haul the longlines
quickly, and have onboard facilities for efficient freezing
storage, in which to keep the valuable catch, and. Brine
freezing tanks are typical on midwater longliners.

Typical fish detection equipment on longliners includes echo sounders.
However, temperature sensors are generally more important than echo sounders in midwater longlining. On larger vessels sonar is usually used.

Industrial Longlining for Tuna

Industrial tuna longliners are usually large vessels, their lengths ranging from 30m to 70 m.
Tuna longlining is carried out in open waters including the high seas. Large commercial tuna longline vessels often stay at sea for months.