A demersal (or set) longline consists of a mainline and snoods with baited (occasionally unbaited) hooks at regular intervals and which is set, in general, on or near the bottom. The number of hooks, distance of snoods on the main line and length of the snoods depends on the target species, the handling capacity and technology used.
Longlines can be set as bottom lines (including on very rough bottom and/or coral reefs) or, less commonly, in midwater or even not far from the surface. Its length can range from few hundred meters in coastal fisheries to more than 50 km in large scale mechanized fisheries.
Incidental catch of turtle, of certain species of sharks or other endangered species are possible negative impacts. Incidental catch of seabirds when setting and/or hauling the line are also possible. Technologies exist for avoiding the catch of seabirds while reducing the bycatch of turtle, sharks or other fish is more difficult.
Source: FAO site, 2017