Longlining uses baited hooks, on offshoots of a single main line, to catch fish at any depth. The line can be anchored in areas too rough for trawling, or set adrift, suspended by floats.
Pelagic, or midwater longline hooks are baited to attract fish such as swordfish, tuna and opah. Unfortunately they also catch sea life such as turtles, sea mammals and birds. Lines can be altered to mitigate bycatch by utilizing: circle hooks that are shaped so the hook won't set in a turtle's mouth, colored bait, weights to sink the bait faster, targeted locationing, and tori lines that scare away sea-birds.