INCIDENTAL CATCH OF MARINE TURTLES IN THE MEDITERRANEAN SEA: CAPTURES, MORTALITY, PRIORITIES INCIDENTAL CATCH OF MARINE TURTLES IN THE MEDITERRANEAN SEA: CAPTURES, MORTALITY, PRIORITIES By Paolo Casale WWF Mediterranean Marine Turtle Programme c/o WWF Italy Recommended citation: Casale P. (2008). Incidental catch of marine turtles in the Mediterranean Sea: captures, mortality, priorities. WWF Italy, Rome. Any reproduction in full or in part of this publication must mention the above bibliographic reference. No photographs from this publication may be reproduced on the internet or elsewhere without prior authorization from the authors. The material and the geographical designations in this report do not imply the expression of any opinion whatsoever on the part of WWF concerning the legal status of any country, territory, or area, or concerning the delimitation of its frontiers or boundaries. Photo Credits. Cover: - Loggerhead turtle captured by a trawler, Italy (D. Freggi). - Loggerhead turtle with a hook in the mouth; captured by a longliner, Italy (P. Casale). - Loggerhead turtle captured by a set net, Tunisia (K. Chouikhi) Back cover: - Loggerhead turtle found adrift entangled with a net, Italy (P. Casale). - Green turtle hung on a tourist boat, Syria (M. Jony). - Loggerhead carapaces sold as guitars, Morocco (M. Aksissou) Drawings: F. Gemma Design: P. Casale For any comment or information please contact: P. Casale, WWF Mediterranean Marine Turtle Programme c/o WWF Italy, Via Po 25c 00198, Roma Italy E-mail: [email protected] www.wwf.it ii TABLE OF CONTENTS Executive summary ............................................................................................................... 1 1. Introduction ....................................................................................................................... 3 2. Relevant parameters for assessing the impact of fishing activity on marine turtle populations........................................................................................................................ 5 2.1. Number of captures .................................................................................................... 5 2.2. Number of deaths ....................................................................................................... 5 2.2.1. Gear-induced mortality........................................................................................ 5 2.2.2. Intentional killing ................................................................................................ 6 2.3. Affected part of the population................................................................................... 6 2.4. Effect on population growth....................................................................................... 6 3. Fishing gear, parameters, and mitigating measures........................................................... 7 3.1. Bottom and Midwater trawls...................................................................................... 7 3.1.1. Parameters affecting catch rate............................................................................ 8 3.1.1.1. Fishing parameters........................................................................................ 8 3.1.1.2. Areas and depths........................................................................................... 8 3.1.1.3. Season and time of the day........................................................................... 8 3.1.2. Parameters affecting mortality rate...................................................................... 9 3.1.2.1. Tow duration ................................................................................................ 9 3.1.2.2. Fishing effort ................................................................................................ 9 3.1.2.3. Temperature.................................................................................................. 9 3.1.2.4. Turtle size ..................................................................................................... 9 3.1.3. Parameters affecting the part of the population caught ..................................... 10 3.1.4. Possible mitigating measures............................................................................. 10 3.1.4.1. Reducing fishing effort............................................................................... 10 3.1.4.2. Reducing catch rate .................................................................................... 10 3.1.4.3. Reducing mortality rate .............................................................................. 10 3.2. Pelagic and demersal longline.................................................................................. 11 3.2.1. Parameters affecting catch rate.......................................................................... 12 3.2.1.1. Fishing parameters...................................................................................... 12 3.2.1.2. Areas and depths......................................................................................... 13 3.2.1.3. Season and time of the day......................................................................... 13 3.2.2. Parameters affecting mortality rate.................................................................... 13 3.2.2.1. Depth and anchorage/weights......................................................................... 13 3.2.2.2. Hook size and shape ....................................................................................... 13 3.2.2.3. Hook position ................................................................................................. 13 3.2.2.4. Branchline....................................................................................................... 13 3.2.3. Parameters affecting the part of the population caught ..................................... 14 3.2.3.1. Area and fishing gear.................................................................................. 14 3.2.3.2. Hook and bait size ...................................................................................... 14 3.2.4. Possible mitigating measures............................................................................. 14 3.2.4.1. Reducing fishing effort............................................................................... 14 3.2.4.2. Reducing catch rate .................................................................................... 14 3.2.4.3. Reducing mortality rate .............................................................................. 15 3.3. Drifting and set net ................................................................................................... 15 3.3.1. Parameters affecting catch rate.......................................................................... 16 3.3.1.1. Fishing parameters...................................................................................... 17 3.3.1.2. Areas and depths......................................................................................... 17 iii 3.3.1.3. Season and time of the day......................................................................... 17 3.3.2. Parameters affecting mortality rate ................................................................... 17 3.3.3. Parameters affecting the part of the population caught..................................... 17 3.3.4. Possible mitigating measures ............................................................................ 17 3.3.4.1. Reducing fishing effort............................................................................... 17 3.3.4.2. Reducing catch rate .................................................................................... 17 3.3.4.3. Reducing mortality rate.............................................................................. 17 4. The marine turtles in the Mediterranean Sea .................................................................. 18 4.1. Caretta caretta (loggerhead turtle) .......................................................................... 18 4.1.1. Nesting sites ...................................................................................................... 18 4.1.2. Marine habitats and migratory routes................................................................ 18 4.2. Chelonia mydas (green turtle).................................................................................. 19 4.2.1. Nesting sites ...................................................................................................... 19 4.2.2. Marine habitats and migratory routes................................................................ 20 4.3. Dermochelys coriacea (leatherback turtle) .............................................................. 20 5. The legal framework for the protection of marine turtles in the Mediterranean............. 23 5.1. Protection of marine turtles...................................................................................... 23 5.2. Management of fisheries .......................................................................................... 25 6. The Mediterranean fishing fleet ...................................................................................... 27 7. Interaction with fisheries in the Mediterranean............................................................... 29 7.1. Objectives and limits................................................................................................ 29