Celoni, F. (1), Azzolin, M. (2), Galante I. (1), Comparetto G. (1), Giacoma C. (2)

1. Bottlenose dolphin (Tursiops truncatus) interaction with gill net for Mullus surmuletus at Lampedusa (Sicily) Celoni, F. (1), Azzolin, M. (2), Galante I. (1), Comparetto G. (1), Giacoma C. (2) 1)CTS – Settore Conservazione Natura, Via Andrea Vesalio 6, 00161 Roma, Italy 2)Università degli Studi di Torino, Via Accademia Albertina 13, 10123 Torino, Italy Abstract In the framework of the LIFE project NAT/IT/000163, a study on interaction between Bottlenose dolphin (Tursiops truncatus) and striped red mullet (Mullus surmuletus) fishing activity has been conducted in Lampedusa waters (South of Sicily, Italy) (Fig.1). From February 2005 to September 2006 the interaction among bottlenose dolphins and Mullus surmuletus fishery was monitored by CTS researchers directly boarded on fishing boats, during 35 surveys. In case of dolphins sightings, the observers collected data on number of animal and behaviour, in order to describe interaction among dolphins and fishery gear. The landed fishes were also weighted and checked for damage at the end of any fishing trip. Statistical analysis shows a significant reduction of total fishery catches, expressed in Kg/square meter of net, when dolphins were present in the fishing area: 0,0015 Kg/m2 of Mullus surmuletus without dolphins (30 surveys) and 7,453*10-5 Kg/m2 with dolphins (5 surveys) (Wilcoxon test, Z=-3.536, P<0.05). The economical impact of the 5 recorded dolphins-fishery interactions out of 35 fishing trip resulted in 182.00 € of damage. supported by • Results • In the study period 35 surveys have been carried out, preliminary results are presented. • The analysis of dolphins presence during fishing activities shows that (Tab.3): • dolphins were present in 14,3% of the total surveys (5 surveys); • in just one occasion dolphins were sighted during setting, in the other ones they were sighted while hauling; • in 3 occasion dolphins didn’t move from the fishing area when fishing vessel approached, but stayed there during hauling for 29 minutes on average (26-37 range); • dolphins mean group size was of 3 animals (2-5 range); • in just one occasion a calf was sighted. • Tab.4 show the results for the analysis of landed fishes, in term of catch composition, total catch and catch for Mullus surmuletus in both condition, with and without dolphins and the results of statistical analysis (Wilcoxon test). • The species caught more frequently with Mullus surmuletus are: Boops boops, Crenilabrus tinca, Dactylopeturs volitans, Diplodus annularis, D. vulgaris, Maena maena, Pagellus erythrinus, Scarus cretese, Scorpaena scrofa and Spondyliosoma cantharus (Fig.2). • In Tab.5 it is showed the economical damage evaluation (ED) for the entire study period. LIFE 2003 NAT/IT/000163 Fig. 1 – Bathymetry of the Sicily Channel and location of Pelagie Islands Tab.3 - Survey without/with dolphins Introduction Starting from 2003, in the framework of the LIFE project NAT/IT/000163, a dolphin-fishery interaction study has been conducted in the Archipelago of Pelagie Islands (South of Sicily, Italy), trough surveys with observers boarded on fishing boats and interview of fishermen. The local fishery fleet consists of 95 boats with fishing licences; the most common systems are bottom trawls, hand lines, trolling lines and, after these, gill nets, long lines, pots and purse seines. The results of interviews for different fishing gears (Tab.1) show that interaction is complained for all of them, but for long lines and pots. The focus of the present study is on set gill net, because of a complained major economical damage. In the study area bottlenose dolphin population is regularly monitored in the area by the Nature Conservation Department of CTS. Mullus surmuletus is fished from August to April, using gill nets with mesh size between 22 and 25 mm, an average overall length of about 1 Km (range 0,5-2,4 Km), an average height of 2 m, and a mean surface of 2.195 square meter. Those gill nets are set at depths ranging from 10 to 45 meter, twice a day, depending on weather condition. Usually the first set is before dawn and the first haul is at sunrise, while the second set is in the afternoon and the second haul is right after sunset. Mean duration of setting, fishing and hauling are respectively: 13 (range 9-15 minutes, SD 2.17), 104 (range 45-231 minutes, SD 42.49) and 45 minutes (range 25-80 minutes, SD 10.26). Tab.4 – Fishery catches without/with dolphins Tab.5 - Estimate of Economic damage of Mullus surmuletus in Euro Fig.2 – Percentage of fishery catches Tab. 1 – Results of interviews • Material and methods • From February 2005 to September 2006 the interaction among bottlenose dolphins and Mullus surmuletus fishery was monitored by researcher directly • boarded on two fishing boats (Tab.2). On board observers collected data on fishing area (net geographical position, depth and distance from shore), • landed fishes (weight of each species), dolphin presence and dolphin-fishery interaction. • The economic damage caused by the loss of catch due the dolphin-fishery interaction was calculated considering: • the average catch loss of the main target species per km of net (L); • the local commercial value of the target species per kg; • the mean net length used daily by each vessel (l); • the fishing days; • the overall frequency of interactions (F). • The frequency of interactions was estimated from the number of interactions observed during the overall number of fishery experiments • (Lauriano et al., 2004). Discussion and conclusion This study represents one of the first attempts in the Mediterranean basin to study depredation by bottlenose dolphins to local fisheries. Since the economy of Lampedusa, one of the biggest island of the Pelagie Archipelago, is mainly based on fishery and tourism, and the Pelagie Archipelago is part of a Marine Protected Area, it is of primary importance to analyse thoroughly the conflict between fishermen and bottlenose dolphins in that area. This study highlights the existence of what was called ‘operational competitive interaction’ (Northridge and Hofman, 1999; Reeves et al., 2001) between bottlenose dolphins and fishermen. The analysis of mean catch shows a significant reduction of fishing catches for Mullus surmuletus in case of dolphins presence, even if the frequency of interaction (estimated from the number of interactions observed during the overall number of fishery experiments) seems lower than in other areas: 0.143 in Lampedusa (2005-2006), against 0.27 (1999), 0.25 (2000) and 0.50 (2001) for Sardinia water (Lauriano et al., 2004). In total the economical impact of the 5 recorded dolphins-fishery interactions out of 35 fishing trip resulted in 182.00 € of damage, about the 15% of the total revenue. Even if the catch loss in the study area doesn’t seem so relevant, it’s important to take in account that for Lampedusa the mean CPUE of striped red mullet is quite lower than the one for other areas (e.g. 2,9 Kg/Km for Lampedusa against 5,301 Kg/Km for Sardinia) leading to a worse perception by fishermen of dolphin depredation. Due to that some fishermen go from set net to trawling with a major impact for the ecosystem. Two kinds of management interventions would be therefore desirable in the area; the first one aimed at limiting the use of less selective gear in order to reduce the undesirable biological effects exerted on resources; the second aimed at finding a system to reduce the interaction between dolphins and fishing nets. References Bearzi G., 2002: Interactions between cetacean and fisheries in the Mediterranean sea. In: G. Notarbartolo di Sciara (Eds.), Cetaceans of the Mediterranean and Black Seas: state of knowledge and conservation strategies. A report to the ACCOBAMS Secretariat, Monaco, February 2002. Section 9: 20 pp. Lauriano G., C.M. Fortuna, G. Moltedo and G. Notarbartolo Di Sciara, 2004: Interactions between common bottlenose dolphins (Tursiops truncatus) and the artisanal fishery in Asinara Island National Park (Sardinia): assessment of catch damage and economic loss. In: J. Cetacean Res. Manage. 6(2): 165–173 pp. Northridge, S.P. and Hofman, R.J., 1999. Marine mammal interactions with fisheries. pp. 99-119. In: J.R. Twiss Jr. and R.R. Reeves (eds.). Conservation and Management of Marine Mammals. Smithsonian Institution Press, Washington and London. 576pp. Reeves, R.R., Read, A.J. and Notarbartolo di Sciara, G. 2001. Report of the Workshop on Interactions between Dolphins and Fisheries in the Mediterranean: Evaluation of Mitigation Alternatives, May 2001, Rome, Italy. Paper SC/53/SM3 presented to the IWC Scientific Committee, July 2001, London (unpublished). Tab. 2 – Boat’s description Acknowledgements We thank all the fishermen of Lampedusa that cooperated with Delta Project. Without them all the collected information would haven’t had a confirmation in the reality. We are grateful to the Management Board of the Pelagie Marine Protected Area for its cooperation. We thank all the people that participated to the data collection. PROVINCIA REGIONALE DI AGRIGENTO promosso da partner Università di Torino