To make it easier to understand fishing methods, we have some illustrations below which explain the various methods used to commercially catch wild caught fish.
Pole & Line
As the name suggests each fish is caught by a pole & line, one by one. Pole and line vessels carry live bait to entice the fish to aggregate around the boat by using bait and/or water spraying. Therefore, pole and line vessels start by catching live bait (generally sardines, anchovies or other type of small bait fish) in inshore waters using a small seine. The fishing gear is composed of a rigid pole of 2 to 3 m (often fiberglass) and a strong short line at the extremity of which hangs a feathered jig mounted on a barbless hook. The pole is held by a fisherman standing on the deck of the boat, about 10 to 20 fishermen fish simultaneously, standing on a platform running along the rear of the vessel, also called bait boat. The tunas are then chilled as soon as possible after capture. Ice slurry is the most efficient cooling medium for rapid chilling of product.
FADs (Fish Aggregating Device)
A Fish Aggregating (or aggregation) Device (FAD) is an object used to attract ocean going pelagic fish such as marlin, tuna and mahi-mahi (dolphin fish). They usually consist of buoys or floats tethered to the ocean floor with concrete blocks. FADs attract fish for numerous reasons that vary by species. Fish tend to move around FADs in varying orbits, rather than remaining stationary below the buoys. Both recreational and commercial fisheries use FADs.
Types of FADs:
- Drifting FADs are not tethered to the bottom and can be natural objects such as logs or man-made.
- Moored FADs occupy a fixed location and attach to the sea bottom using a weight such as a concrete block. A rope made of floating synthetics such as polypropylene attaches to the mooring and in turn attaches to a buoy. The buoy can float at the surface (lasting 3-4 years) or lie subsurface to avoid detection and surface hazards such as weather and ship traffic. Subsurface FADs last longer (5-6 years) due to less wear and tear, but can be harder to locate. In some cases the upper section of rope is made from heavier-than-water metal chain so that if the buoy detaches from the rope, the rope sinks and thereby avoids damage to passing ships who no longer use the buoy to avoid getting tangled in the rope.
- Smart FADs include sonar and GPS capabilities so that the operator can remotely contact it via satellite to determine the population under the FAD.
A purse seine is made of a long wall of netting framed with floatline and leadline (usually, of equal or longer length than the former) and having purse rings hanging from the lower edge of the gear, through which runs a purse line made from steel wire or rope which allow the pursing of the net. For most situations, it is the most efficient gear for catching large and small pelagic species that is shoaling.
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.
Trawl nets are cone-shaped (made from two, four or more panels) which are towed, by one or two boats, on the bottom or in midwater (pelagic). The cone-shaped body ends in a bag or coded. The horizontal opening of the gear while it is towed is maintained by beams, otter boards or by the distance between the two towing vessels (pair trawling). Floats and weights and/or hydrodynamic devices provide for the vertical opening. Two parallel trawls might be rigged between two otter boards (twin trawls). The mesh size in the codend or special designed devices is used to regulate the size and species to be captured.