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the catching of fish and squid with long-lined fishing gear having hooks on the ends. Longline fishing is used mainly for valuable fish, such as tuna and salmon, that live in small concentrations at the bottom or in the open sea.
Longlines may be horizontal or vertical. A horizontal longline consists of a main line, to which are attached branch lines with hooks and supporting buoys. In a bottom longline the main line is as much as 4 km long; the branch lines measure 0.7–1.5 m and are spaced 1.5–2.5 m apart. Drifting longlines, the type used for tuna, measure as much as 120 km long; the branch lines are 20–25 m long and are spaced 45–55 m apart.
A vertical longline for squid consists of a line as much as 100 m in length and equipment weighing 300–800 g, including 20–80 lures, each with 30–40 hooks; the distance between the lures is 20–60 cm.