In June 1995, a 12 days research cruise was organized in the Ligurian and North Tyrrhenian Sea to record cetacean sounds with the towed array of the University of Pavia. The cruise was supported by the Italian Navy within the ENCY 95 (European Nature Conservation Year) activities. The hydrophone was towed for 111 hours (out of 12 cruising days) at speeds up to 14 km/h; listening stations were held on a 24h schedule for at least 10 min every half an hour. One sperm whale was detected and located. It was heard at night and acoustically tracked for the following 8 hours. Within this period the whale was sighted at the surface 5 times, while 8 complete dives were continuously recorded on DAT tapes (about 6 hours of recording). The recordings are now archived at the Cetacean Sound Library held at the Centro. New methods of sound analysis were developed to make the analysis of such long recordings easier and to give compact pictures of whole dives. Our real-time analysis software was modified with new procedures able to 1) automatically detect and count clicks, 2) measure and save inter-click intervals, 3) save packed representations of the click sequences and display autocorrelograms to show the evolution of inter-click intervals over long periods of time. The analysis of the recordings shows that all the recorded dives were characterized by a typical and constant clicking pattern at their beginning. The duration of the acoustical emission, measured from the first click to the last click of each dive, was on average 27 minutes 30 seconds, while the silence related to the surfacing was on average 13 minutes and 11 seconds.
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