Longline
The drift longline deployed over the continental shelf (for tuna-like species) or offshore waters (for swordfish, albacore and bluefin tuna) is considered as the main threat to marine turtles in the Mediterranean. Over 50.000 specimens are estimated to be bycaught with pelagic longliners with a mortality of 40% mainly in Spain, Morocco, Italy, Greece, Malta, Libya. Some authors estimated an annual catch of about 35.000 specimens with pelagic longline only for the western and central Mediterranean Sea. The Western Mediterranean Sea is one of the main areas of concentration for juvenile and adult loggerheads, as well as for targeted fishing species, such as swordfish. Spain is the country with the highest number of turtle captures per year, followed by Morocco and Italy. This is not surprising since it is known that the occurrence of a high concentration of sea turtles in the western basin of the Mediterranean Sea is due to the entrance of specimens from the Atlantic Ocean via Gibraltar. The Spanish surface longline fleet mainly targets swordfish throughout the year, as well as bluefin and albacore tuna during summer periods. The incidental capture of loggerheads extends from spring to late autumn, with most captures occurring in the summer.
The most abundant catches are detected around the Balearic Islands; some authors estimated an annual catch of about 15.000 specimens of C. caretta. Turtles are very common also in Italian waters migrating from the eastern to the western Mediterranean basin and vice versa through the Straits of Messina and the Strait of Sicily. The two corridors are characterized by high fishing pressure, but the drift longline is the most impacting fishing gear. Italy is estimated to be responsible for 10.000 captures per year. Bycatch by the EU and non-EU industrial longline fleets operating in the area (Japanese, flag of convenience) could lead to even a worst situation.
Demersal longlines mainly in Tunisia, Libya, Greece, Turkey, Italy, Egypt, Morocco seem to be responsible for about 35.000 capture events with a mortality of about 45%.
The mortality induced by longlines is very difficult to assess; direct mortality appears to be low, but studies made by rescue centres show a high post-release mortality, both in the short and in the long-term. It is realistic to consider that fixed longline has the potential to be more harmful than pelagic longlines, given the fact that the by-caught animals do not have any chance to reach the surface to breath. Mortality strongly depends on the hooks position in different parts of the digestive tract (mouth, oesophagus, stomach, intestine). Albacore and bluefin tuna longlines produce higher direct mortality than swordfish longlines. This is probably because of the gear structure and hook size but it could be also due to the fishing depth or to the higher catch amount that could sink the gears affecting turtle mortality by reducing breath possibilities.
