Surface longline gears are used to fish different species, mainly albacore Thunnus alalunga (Bonnaterre,1788), bluefin tuna Thunnus thynnus (Linnaeus, 1758), and swordfish Xiphias gladius Linnaeus, 1758, and are consideredhighly dangerous for threatened marine turtles. Loggerheads Caretta caretta (Linnaeus, 1758) can be incidentally capturedby surface longlines. A number of captured individuals die during the fishing operation, which we consider direct mortalitydue to fishing.
http://209.85.135.104/search?q=cache:g_JVH50lW5IJ:www.icm.cs...

Longline fisheries catch fish on a long line, which is, simply, a long piece of rope or nylon that lies in the water supporting baited hooks. There are two types of longlining: surface longlining and bottom longlining.

Surface longlines are suspended about 200 m beneath the surface and are used to catch tuna and swordfish. They might exceed 100 km in length and carry 3,000 baited hooks suspended on 40 m-long branch lines spaced 50 m apart. When longlines are paid out from vessels seabirds attack the baited hooks, get caught or entangled in gear, are drawn underwater and drown.
http://www.birdsaustralia.com.au/albatross/longline.html

This paper presents overall scientific estimations on bycatch landings by species, or groups of species,
carried out by the Spanish surface longline fleet targeting swordfish (Xiphias gladius) in the Pacific
Ocean. The mean level of bycatch landed by the Spanish fleet from the beginning of the fishing activity in
1990 until the year 2005 accounted for 42.6% of the total weight landed (target species and bycatch
combined).
http://www.iattc.org/PDFFiles2/BYC-6-INF-A-ESP-SWO-fishery-b...