Longlining is a passive fishing technique using baited hooks. The full fishing gear consists of various branch lines – between 100 and 200 – which hang from a main line (kept on the surface by buoys) onto which the hooks are attached. In the case of the Spanish longlining fleet working in the Mediterranean, the total length of the gear can exceed 40 kilometres and use more than 2,000 hooks, while the large industrial fleets are capable of setting 100 kilometres of longlines.
The hooks are baited with small pelagic fish (pilchard, mackerel,etc. ), cephalopods or artificial bait (sometimes including lights) to attract swordfish. But this fishing method can also catch other carnivorous species, such as tuna, dolphins and sea turtles.
Most longlining fleets operated in the North Atlantic target swordfish, tunas and sometimes sharks. Sea turtles constitute unwanted bycatch, as well as other species including rays, ocean sunfish, Atlantic pomfrets, dolphinfish and some species of marlins, tunas and sharks.
Although some of these species are commercialised along with the target species, others are thrown back into the sea.