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Different types of fishing methods
Gillnets
Gillnets are a single wall of monofilament netting, set at the surface, in midwater or just above the seabed. The net hangs from a floated headline and catches fish as they swim into the net and become entangled in a single mesh by their gill covers. Gillnets are targeted at demersal and pelagic roundfish, such as herring, mackerel, cod, pollack, bass and salmon, although bottom set nets can also catch crustaceans.
Tangle nets
Tangle nets are similar to gillnets in that they are a single wall of netting suspended from a floated headline. However they differ from gillnets as they are more loosely set from the headline, creating a baggy effect which then tangles the target species in several meshes. The main target species for tangle nets are fish with spines, such as rays and crawfish.
Trammel nets
Much less common than either gillnets or tangle nets, trammel nets comprise three walls of monofilament netting. The two outer nets are large meshed panels which sandwich an inner panel of finer mesh, which is twice as big as the outer panels, allowing it to bag when fish swim into it. The nets catch target species as they swim through the large mesh outer panels and become trapped in a pocket of finer mesh created by their own forward swimming motion. The mesh size of the outer panels can be adjusted to different target species by adjusting the head and footrope settings.
Materials (Gill, Tangle & Trammel)
The netting is mostly woven from fine nylon twine, which is practically invisible underwater under most conditions. Twine thickness ranges from 0.2 - 0.9mm. Several types of twine are available and the choice is a compromise between stiffness for ease of handling and softness for catching efficiency. Mulit-monofilament twine is commonly used and this consists of 8-12 strands of thin monofilament, about 0.15 mm thick, lightly twisted together. Scottish vessels are not permitted to carry monofilament nets under 250mm mesh size within 6 miles of the coast.
In recent years, mutifilament netting has become increasingly popular. This type of net comprises several very fine strands of monofilament polypropylene instead of the thicker single strands. It creates a greater capability for entanglement and generally yields a better catch than monofilament netting, but also has a higher capacity for bycatch.
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