LONGLINES - article Mary Stuart p2 of 3

Longlines are used mainly to catch large bigeye, albacore
and yellowfin tuna in tropical waters, as well as northern
bluefin and southern bluefin tuna in temperate waters.

Tuna - Photograph courtesy NOAA

The longline used in tuna fishing is made from a series is of units, sometimes known as "baskets", each of which consists of a main horizontal line about 250 to 800 m long, with between 4 and 15 branch-lines, each with a wire leader and a hook.

Fishing takes place in sub-surface areas, and at depths from 100m to 300m (maximum depths of 175 m for the conventional longlines and of 300 m for the deep longlines). The depth where the hooks are set in the water column is a crucial element. It can be regulated either by adjusting the length of float-line and/or the speed of shooting, and to a lesser extent, by modifying the length of the branch-lines.
A typical set consists of 200 or more units or "baskets" connected together, with a buoy at each connection, and a total of approximately 3000 hooks.

Baiting longlines

The baiting of hooks may be done manually or by
means of a baiting machine. Various fish species,
such as mackerel and squid are used for bait.
Before the line is set, the bait is removed from the
freezer and thawed partially before use.
In the manual baiting operation, the crew member
responsible for attaching the bait to the hook does
so by piercing the bait with the hook at the time of
casting the branch line, which is already connected
to the main line.

When baiting machines are used, they are usually
located aft of the line storage rails. The bait is fed
into the machine via a spiked conveyor belt. It is
essential that the bait be firm as it helps to ensure
a good hooking rate. Baiting machines are usually
designed to bait 10 000 -20 000 hooks a day.

Diagram to show hook attachment methods

Setting longlines

A typical set consists of 200 or more "units/baskets" connected together, with a buoy at each connection, and a total of about 3000 hooks.
The gear is released in a continuous way, each hook being baited just before leaving the vessel's deck.
The vessel steams at between 9.5 knots and 11.5 knots. The longline is paid out from the aft storage wells on the upper deck through a series of PVC pipes and a hydraulic line feeder, situated on the lower deck amidships, at a rate of about 450 m per minute (27 km per hour).
The depth of the mainline can be varied by changing the speed of the feeder and the speed of the vessel.
The rate at which branchlines (snoods) and buoylines are attached to the mainline, and therefore the space between snoods, is controlled from the wheelhouse.
Radio buoys are used for locating the line at the start of the haul or in the event of a broken line.
Between 2500 and 3000 hooks are set over a total distance of about 100 km, taking about five or six hours to complete each set. At least five crewmembers are required for the setting.
After the last radio buoy is set, the crew retire for about four hours before the start of the hauling operation.
In general the starting time for hauling the lines depends upon the number of baskets set.

Hauling longlines

Hauling usually takes at least 11 hours, and requires at least a dozen crewmembers. The last radio buoy set is usually the first to be hauled on board. It is located with the help of the radio direction finder or by radar, and is hauled on board and detached from the mainline.

The mainline is threaded over roller guides and through the hydraulic mainline hauler. The speed of recovery is controlled by a crewmember. The mainline coils under its own tension from the hauler onto a conveyor belt which carries it across the deck from starboard to port side. Any tangles in the mainlines are removed as it moves along on the conveyor belt.

The vessel steams along the mainline at an average speed of about 6 knots, with the line retrieved over the starboard side at a rate of between 150 and 250 m per minute.
Branchlines are unclipped off the mainline as they come over the side of the vessel or after they go through the line hauler.

The snoods are coiled, either by hand or with an automatic coiler, and are tied off around the hook with a loop of the line near the clip, then packed into bundles of approximately 20 in baskets.

These bundles or baskets and the buoys are placed at intervals onto a conveyor belt on the port side of the vessel. This takes them to the crewmember who is packing the mainline into the aft wells and they are then stacked at the stern ready for the next set.

Landing the catch

When a large fish is detected on a line, the vessel slows,
and may turn to starboard to follow the fish.

When the fish is brought alongside the vessel,
a gaff or a harpoon is used to land it, spearing the fish in the head.
Once landed, the monofilament line is cut so the hooks remain in the mouth until dressing. This practice makes handling of the catch much easier.

Fish handling on board

A live catch lifted onto the deck must be killed immediately, because it is very dangerous for the crew to work beside a live catch.
With tuna, the caudal fin is removed immediately with a saw. The fish are then gutted and sent to the freezing chambers.
The catch is then washed and put in the pre-cooler room.

In the Southern Ocean, tuna fleets set over 200 million long-lines a year. These fleets operate beside purse seiners, trawlers and other fisheries to catch some of the most sought after fish in the world.