Using lesions to assess the impact of fisheries on loggerhead turtles

One of the functions of the WWF Sea Turtle Rescue Centre of Lampedusa, Italy, (CRTM) has been to work closely with local fishermen and other sea-users. This collaborative approach has resulted in thousands of loggerheads arriving at CRTM. We analyse the period between January 2003 and December 2006; in this period we observed lesions associated with human activities in 246 loggerhead sea turtles of 926 referred (26,56%). We considered the type of lesions (their cause and location in the animal) and related these to capture methods (longline 14.04%, trawled 62.74%, taken by hand 20.63%, nets 1.94%, stranded 0.65%). In 215 turtles (87.40%) we found an interaction with longline: in 186 animals (75.61%) lesions were located in the alimentary canal due to hook and monofilament line ingestion, in 9 cases (3.66%) hooks were embedded in flippers or neck causing external lesions and in 20 turtles (8.13%) we observed serious exterior trauma, caused by nylon line restricting blood flow to limbs. We hospitalized 12 turtles (4.88%) with fractures on the carapace or plastron; all them were captured by trawling and lesions were caused by impacts with big stones in the final part of fishing net. Their increasing number during years seems to show the better relations with trawling fishermen, so important to understand what happens in seawork. In the turtles that ingested hooks we could determinate the location: 69 were in the mouth, 79 in oesophagus, 14 in the stomach and 14 in intestines too; 6 turtles had more than 1 hook lodged in different portions of alimentary canal. Another 4 turtles had only fishing-line, without hook, extended through the entire alimentary canal. The majority of turtles with hooks in the upper digestive tract (mouth and oesophagus) were caught by longline (70.94%), and were usually fit enough to face surgical intervention. In contrast turtles presenting hooks or line in the lower digestive tract (stomach or intestine) were in serious condition and in most cases were taken manually (67.95%). In the 246 cases observed, 53 turtles (21,54%) died owing to seriousness of lesions: in 31 of them (58.49%) the cause of death was lesions in the lower digestive tract (occlusions, tears, constrictions, invaginations), because of hooks and especially fishing-lines; in the other 22 turtles (41.51%) the cause of death is correlated to trawlings’ lesions (fractures of carapace and plastron, drowning, etc.). These data seem to confirm that ingestion of hooks and line are the most frequent anthropogenic cause of lesions in observed loggerheads. Moreover, foreign bodies remaining for a long period of time, or that pass through the alimentary canal, cause serious pathology and are the principal cause of death in stranded turtles. These conclusions drive us to consider as a target the timely recovery of wounded animals, so to improve surgery success.