One of the main goals of the EU-Life Project Urgent conservation measures of Caretta caretta in the Pelagie islands (LIFE99NAT/IT/006271) consists in evaluating the impact of local fisheries on the Loggerhead Turtle's mortality rates in the waters surrounding the island of Linosa (35° 51'N 12° 51'E, Pelagie Islands, South of Sicily). Reports of by-catches of Caretta caretta collected since 1994, in fact, suggest that long-line fishing has a strong impact on the local population. To develop suitable conservation measures in this respect, we created a network of local fishermen willing to co-operate in order to: 1) take turtles to the rescue centre, in order to de-hook and treat them medically before release (during summer 2000 a total of 158 turtles were treated, measured and marked at the Linosa rescue centre), and 2) to develop an experimental fishing procedure, suitable for reducing by-catches. To the last purpose, we first made a survey of local fishing procedures. In order to try and reduce captures of turtles, but selectively not of swordfish (Xiphias gladius), we investigated the possibility (1) to reduce bait attractiveness, (2) to decrease the overall attractiveness of the fishing device and (3) to utilise acoustic deterrents. Experiments were initially run in a round tank having a 10 m diameter at the Cattolica Aquarium. Later on, thanks to the co-operation of local fishermen, results were tested in the Sicilian Sea, during fishing trips. The bait's (Scomber scomber) smell and colour were tested to see whether the yellow, red or blue colour make baits less attractive and/or more difficult for the turtles to detect. The bait's smell demonstrated to be an important component for its detection by turtles. Smell-less artificial baits, in fact, are generally unattractive for turtles. The effect of the bait's colour is doubtful, since individual turtles may show a colour preference, but different colours attract different turtles. No attractive effect of lights set on the line floaters was evident. Finally, we played back sounds (both pure tones and noises) to elicit a possible avoidance response and we found that turtles react to low frequency sounds (0-300 Hz). Results obtained with artificial baits on swordfish fisheries will also be discussed.
Urgent measures for the conservation of Caretta caretta: experimental evaluation of by-catch reduction devices.
BALLETTO, Emilio;GIACOMA, Cristina;PIOVANO, SUSANNA;
2001-01-01
Abstract
One of the main goals of the EU-Life Project Urgent conservation measures of Caretta caretta in the Pelagie islands (LIFE99NAT/IT/006271) consists in evaluating the impact of local fisheries on the Loggerhead Turtle's mortality rates in the waters surrounding the island of Linosa (35° 51'N 12° 51'E, Pelagie Islands, South of Sicily). Reports of by-catches of Caretta caretta collected since 1994, in fact, suggest that long-line fishing has a strong impact on the local population. To develop suitable conservation measures in this respect, we created a network of local fishermen willing to co-operate in order to: 1) take turtles to the rescue centre, in order to de-hook and treat them medically before release (during summer 2000 a total of 158 turtles were treated, measured and marked at the Linosa rescue centre), and 2) to develop an experimental fishing procedure, suitable for reducing by-catches. To the last purpose, we first made a survey of local fishing procedures. In order to try and reduce captures of turtles, but selectively not of swordfish (Xiphias gladius), we investigated the possibility (1) to reduce bait attractiveness, (2) to decrease the overall attractiveness of the fishing device and (3) to utilise acoustic deterrents. Experiments were initially run in a round tank having a 10 m diameter at the Cattolica Aquarium. Later on, thanks to the co-operation of local fishermen, results were tested in the Sicilian Sea, during fishing trips. The bait's (Scomber scomber) smell and colour were tested to see whether the yellow, red or blue colour make baits less attractive and/or more difficult for the turtles to detect. The bait's smell demonstrated to be an important component for its detection by turtles. Smell-less artificial baits, in fact, are generally unattractive for turtles. The effect of the bait's colour is doubtful, since individual turtles may show a colour preference, but different colours attract different turtles. No attractive effect of lights set on the line floaters was evident. Finally, we played back sounds (both pure tones and noises) to elicit a possible avoidance response and we found that turtles react to low frequency sounds (0-300 Hz). Results obtained with artificial baits on swordfish fisheries will also be discussed.
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