TURSIOPS TRUNCATUS POPULATION AT LAMPEDUSA ISLAND (ITALY): PRELIMINARY RESULTS. Pace D.S., Pulcini M. and Triossi F.

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1 TURSIOPS TRUNCATUS POPULATION AT LAMPEDUSA ISLAND (ITALY): PRELIMINARY RESULTS Pace D.S., Pulcini M. and Triossi F. A.A.M. Via Vitellia 15/b - Rome - Italy INTRODUCTION. The most comprehensive studies of free-ranging dolphins have focused on accessible coastal populations; several, have examined the social system, ranges, behavior, and other aspects of the life history of bottlenose dolphin (Tursiops truncatus) (Würsig, 1984; Scott et al., 1990; Wells, 1991; Bearzi et al., 1997). Some specific surveys on this species have been undertaken in the Mediterranean Sea; however, the dolphins occurrence along Lampedusa Island coasts (Pelagie s Archipelago, Sicily) had been still uninvestigated. In the last few years, the presence of an inshore population of bottlenose dolphin along the coasts of Lampedusa Island was first noted and reported by local fishermen. Due to their coastal nature, bottlenose dolphins have frequent contact with human activities, and many interactions with fishery operations have been described in this area (Mazzola et al., 1996). Tursiops truncatus commonly interact with fisheries around the world (reviews in Shane et al., 1986; Fertl and Leatherwood, 1998). However, a limited number of these studies has elaborated on the nature of the association, and few attempts to quantify the effects of this relationship on feeding ecology, sociality, inter-specific interactions, or movements were reported. The primary goal of this study was to collect systematic data on the habitat-use patterns of bottlenose dolphins along Lampedusa Island in order to provide a better understanding of their local ecology and behaviour. In addition, the purpose of these observations was also to examine animal association and/or feeding during trawling fishing activities and related behaviours. MATERIALS AND METHODS. Dedicated research surveys during July through September 1996 and 1997 were conducted. Sightings of bottlenose dolphins were recorded by a 4.5 inflatable powered outboard, and few observations were made from two land-bases sites. Photographic surveys allowed recognisable dolphins to be reidentified later, in order to define the home range and number of dolphins in the study area (FIG. 1). All the pictures were taken with a 35mm camera using a 35-80mm, mm and mm lenses. Because groups were typically small, it was possible to record the visible behaviours of all individuals simultaneously every 3 minutes using a check-list (instantaneous sampling, Altmann, 1974) and in an ad libitum manner (Altmann, 1974) using a tape-voice recorder. Data recorded included date, time, location, direction of travel, distance between and orientation of individuals, relative speed of travel, group size and composition (numbers of adults, juveniles and calves), dive duration, and occurrence of discrete behaviours. Sea conditions, other environmental factors and the number and the type of the nearby vessels were also noted. When dolphin group was observed in association with trawls, the boat s operational state was recorded. RESULTS. A total of approximately 200 km 2 of water was covered during the two years study, and 576 hours in the field searching for dolphins were spent. Animals were sighted with higher frequency near two zones - named Albero Sole (N) and Punta Sottile (S-E) - at an average of 50 m in depth and 2,7 km offshore. Bottlenose dolphins were reported within the

2 area on 109 occasions (n=41 in 1996 and n=68 in 1997), with the recording of 332 specimens (n=125 in 1996 and n=207 in 1997) (see TAB. 1). Group size ranged from 1 to 12 individuals in 1996 (mean 3,048; s.d. 2,213; mode 2), and from 1 to 13 in 1997 (mean 3,044; s.d. 2,262; mode 1). A total number of 51 recognisable individuals were catalogued by the photoidentification method (n=27 in 1996 and n=24 in 1997), and 12 were sighted more than one time. Total age class composition of the groups was: 267 adults, 43 juveniles and 18 calves and newborns. Approximately 47 hours of behavioural observations were recorded during these encounters, with a total number of 928 records of instantaneous sampling every 3 minutes. All major activity patterns and specific events were noticed, in order to identify the main behavioural traits such as socializing, milling, resting, travelling and mixed behaviours (defined according to Shane, 1990) (see FIG. 2). Bottlenose dolphins were occasionally seen feeding on schooling fish near the surface, showing well defined group formations (i.e. circle, carousel, kettle; see Bel kovich, 1991), lunge at high speed, large irregular splashes, and frequent respiration. Usually, the water depth did not allow to determine if the animals were certainly engaged in foraging operations. In this case, feeding groups were identified by tail-stock or fluke-up modality prior to dive (Shane, 1990), less frequent surfacing, dives longer than those observed in the surface feeding pattern and/or clustered short dives followed by a long one, and distribution in a limited area. Moreover, other two feeding-related categories - defined as SEARCHING (Bel kovich, 1991) and TRAWLING - were scored. While the first one indicated the looking for prey activity, in which the dolphins scattered through a specific water area moving in varying directions, showing irregular dives and no established group geometry, the second one involved dolphins following trawlers and feeding on their by-catch. This last point was carefully checked and four different behavioural patterns were measured in order to focus the influence of the fishing operations on cetacean feeding behaviour: TRW1=following the trawls at a distance of m (53%); TRW2=feeding on the by-catch, close to the boat, at a distance of 5-10 m (16%); TRW3=waiting for the by-catch withdraw and trash fish (23%); TRW4=feeding of trash fish discarded at the end of a trawl (8%) (FIG. 3). A close association between animals and trawling boats was observed with a total frequency of 57 times (52,3%). Finally, three sightings of Stenella coeruleoalba, and one of Delphinus delphis associated with Tursiops truncatus, were performed in the study area. DISCUSSION. Bottlenose dolphin is cosmopolitan species and exhibits a series of forms which differ behaviourally and morphologically (Ballance, 1992). Results of this study - pertaining only to the inshore coastal form - showed that Lampedusa s waters were particularly interesting for the cetological fauna occurrence (Pulcini et al., 1997). In fact, a certain degree of fidelity was noticed through the photoidentification results. The peculiar distribution of the sightings, not related to a particularly focused effort in these areas, suggested a probable relationship with environmental factors: while the dolphins presence to the North, at Albero Sole, seemed to be not associated with any particular features, their appearance at Punta Sottile (S-E) was specifically related to trawls and shallow waters. Other authors have already reported that dolphins follow fishing boats, adapting their behaviour at taking advantage of human activity (Norris and Prescott, 1961; Leatherwood, 1975; Würsig, 1986; Corkeron et al., 1990; Shane et al., 1986; Shane, 1990; Bearzi and Notarbartolo di Sciara, 1997; Fertl and Leatherwood, 1998). Bottlenose dolphin is often described as a species displaying a large degree of behavioural plasticity, best exemplified by a wide variety of feeding behaviours adapted to particular habitats. As a consequence, the presence of trawling

3 boats seemed to influence the dolphins foraging strategy in the study area because the animals followed a trawling vessel probably feeding on organisms stirred-up by the trawl, on fish which passed through the mesh, or may be picking out fish entangled in the net s mesh. Opportunistic feeding in association with fisheries is perhaps best exemplified by feeding on culled and discarded trash fish. However, the effect of this method of feeding on aspects of the dolphin s behavioural ecology has not been investigated, although normal searching and feeding activities resulted to be inverse proportionally to the trawling behaviour. In addition, the observation of some mother-calf pairs associated to trawling boats suggested that bottlenose dolphins could have learned the advantages of following and feeding in conjunction with trawls. In this respect, it has been speculated that the calves may learn this foraging behaviour by observation and participation (Shane et al., 1986). Although these observations are preliminary, the recorded data suggest more detailed longterm studies on this bottlenose dolphin population should be needed. Data gathered using standardised methods could provide quantitative results for this specific population which could also be used for detailed comparative purposes. ACKNOWLEDGMENTS. We are grateful to the many individuals involved in the collection of these data: Stefano Cerioni for his constant help, Marco Melodia for providing additional photographic material, Alvise Zannetti for his precious field assistance, and the local fishery community. Special thanks to the Italian Coast Guard for providing help and host in the CP 244 and CP 279. We also thank CTS - Dipartimento per l Ambiente for the logistic support. We are also very grateful to Raffaella Tizzi for her kindness in the poster realisation. Finally, we would like to thank the two anonymous referees for useful comments to improve the manuscript. REFERENCES Altmann, J Observational study of behavior: Sampling methods. Behaviour 49: Ballance, L. T Habitat use patterns and ranges of the bottlenose dolphin in the Gulf of California, Mexico. Mar. Mamm. Sci. 8(3): Bearzi, G. and Notarbartolo di Sciara, G Bottlenose dolphins following bottom trawlers in the Kvarneric (Northern Adriatic Sea). Pp In European Research on Cetaceans 11. Proc. 11 th Ann. Conf. ECS, Stralsund, March, 1997 (Eds. P.G.H. Evans, E.C.M. Parsons and S.L. Clark). European Cetacean Society, Cambridge, England. 324pp. Bearzi, G., Notarbartolo di Sciara, G. and Politi, E Social ecology of bottlenose dolphins in Kvarneric (northern Adriatic Sea). Mar. Mamm. Sci. 13(4): Bel kovich, V.M., Agafonov, A.V., Yefremenkova, O.V., Kozarovitsky, L.B. and Kharitonov, S.P Dolphin herd structure. Pp In Dolphin societies: Discoveries and Puzzles. (Eds. K. W. Pryor and K.S. Norris). University of California Press. 397pp. Corkeron, P.J., Bryden, M.M. and Hedstrom, K.E Feeding by bottlenose dolphins in association with trawling operations in Moreton Bay, Australia. Pp In The Bottlenose Dolphin (Eds. S. Leatherwood and R.R. Reeves), Academic Press, San Diego. 653pp. Fertl, D. C Occurrence, movements, and behaviour of bottlenose dolphins (Tursiops truncatus) in association with the shrimp fishery in Galveston Bay, Texas. M. Sc. Thesis, Texas A&M University, College Station, Galveston, TX. 116pp. Fertl, D. C. and Leatherwood, S Cetaceans interactions with trawls: a preliminary review. J. Nortw. Atl. Fish Sci. 22:

4 Leatherwood, S Some observations of feeding behavior of bottlenose dolphins (Tursiops truncatus) in the northen Gulf of Mexico and Tursiops (cf T. gilli) off southern California. Mar. Fish. Rev. 37(9): Mazzola, S., Guerrini, A., Bonanno, A., Patti, B. and Giusto, G. B Preliminary study on census data about the interaction between dolphins and fishing activity in the Sicilian fisheries. Pp In European Research on. Cetaceans 10. Proc. 10 th Ann. Conf. ECS, Lisbon, March, 1996 (Ed. P.G.H. Evans). European Cetacean Society, Cambridge, England. 334pp. Norris, K.S. and Prestcott, J.H Observations on Pacific cetaceans of Californian and Mexican waters. Univ. Calf. Publ. Zool. 63(4): Pulcini, M., Pace, D.S., Triossi, F. and Cerioni, S Preliminary results on the occurrence of bottlenose dolphin Tursiops truncatus along Lampedusa island coasts. Pp In European Research on Cetaceans 11. Proc. 11 th Ann. Conf. ECS, Stralsund, March, 1997 (Eds. P.G.H. Evans, E.C.M. Parsons and S.L. Clark). European Cetacean Society, Cambridge, England. 324pp. Scott, M.D., Wells, R.S. and Irvine, A.B A long-term study of bottlenose dolphins on the west coast of Florida. Pp In The Bottlenose Dolphin (Eds. S. Leatherwood and R.R. Reeves). Academic Press, San Diego. 653pp. Shane, S.H Behavior and ecology of the bottlenose dolphin at Sanibel Island, Florida. Pp In The Bottlenose Dolphin (Eds. S. Leatherwood and R.R. Reeves). Academic Press, San Diego. 653pp. Wells, R.S The role of long-term study in understanding the social structure of a bottlenose dolphin community. Pp In Dolphin societies: Discoveries and Puzzles. (Eds. K. Pryor and K.S. Norris). University of California Press. 397pp. Würsig, B Aspects of the natural history of bottlenose and dusky dolphins. Nat. Geograph. Res. Rep. 1975: Würsig, B Delphinid foraging strategies. Pp In Dolphin cognition and behavior: a comparative approach (Eds. R.J. Schusterman, J.A. Thomas and F.G. Wood), Lawrence Erlbaum Associates, Hillsdale and London. 379pp. Year No. of Sightings No. of Indivs. sighted TABLE 1. Sightings at Sea Sightings from Land Sightings with Trawlers Tot

5 FIGURE 1. Sightings distribution along the Lampedusa Island coasts Resting 2% Mix 6% Milling 4% Travelling 31% Trawling 33% Searching 14% Feeding 9% Socializing 1% FIGURE 2. Time spent in each behaviour pattern TRW3 23% TRW4 8% TRW2 16% TRW1 53% FIGURE 3. Trawling behaviour composition