Mortality induced by drifting longline hooks and branchlines in loggerhead sea turtles, estimated through observation in captivity

1. Drifting longlines are considered a major threat to endangered sea turtle populations worldwide. However, for a number of reasons, the mortality rate of captured turtles is not known with any certainty. 2. Information on 409 loggerhead turtles (Caretta caretta), collected during the day-to-day activities of a turtle rescue centre in Lampedusa island, central Mediterranean, in the period 2001-2005 has been analysed. 3. Observations indicate that: (i) drifting longlines are a major cause of mortality for sea turtles in the area; (ii) in addition to the hook, the piece of line attached to it (branchline) can easily cause death if it is long enough and well-anchored; (iii) hooks and branchlines cause death in the short and long term, respectively; (iv) a turtle with a hook in the lower oesophagus/stomach has a very low chance of surviving the combined effect of hook and branchline; (v) the mortality of turtles with a hook in the mouth or higher oesophagus is probably important, though less than that of turtles with a hook in the lower oesophagus/stomach; (vi) in the study fishery, the average mortality of a turtle caught by a drifting longline is probably much higher than 30%. 4. Without specific investigations on the mortality of turtles with hooks in the mouth or higher oeasophagus, which are usually removed, the mortality induced by drifting longlines will remain unknown, preventing a full understanding of the effect on population growth and the real effectiveness of conservation measures such as use of different hooks and fishing depths, and proposals for adequate fishery management measures. 5. The number of turtles captured by drifting longlines should be drastically reduced, and because of the above uncertainty and the socio-economic importance of the fishery sector, an ecosystem-based management scheme should be promoted that is not limited to addressing only the turtle issue. Copyright © 2007 John Wiley & Sons, Ltd.