Sperm whale codas in the Northern Ionian sea (Italy), new elements to understand the Mediterranean population [abstract]

Zardin, F, Pavan, G, Ficetola, G F, La Manna, G, Internullo, E & Riccobene, G (2012). Sperm whale codas in the Northern Ionian sea (Italy), new elements to understand the Mediterranean population [abstract]. Bioacoustics, Volume 21 (1): 61

The NEMO-OvDE platform, deployed on the seabed at a depth of 2050 m, 21 km off the coast of Catania in Sicily (Italy), has provided the opportunity to better understand the presence and behaviour of sperm whales in the area. Equipped with four wideband hydrophones (30Hz-40kHz) forming a tetrahedral array of 1 m side, the platform sent digital data to the land station continuously 24h a day from January 2005 to November 2006. 7359 samples, for a total of 613 hours, were recorded and analyzed to determine the presence of sperm whales. Analyses were performed by trained operators with the use of SeaPro, a real-time spectrographic software, to distinguish species, number of individuals present and sound categories emitted. Sperm whale presence is considered as low density in the Ionian sea by an acoustic survey of IFAW in 2004 and by other works done in the vicinity. However, in our study, an unexpected presence of animals was found, with 23% of files containing animals in both years. Then, we focused our study on codas, sounds typical of social groups and with a geographical connotation, which for the Mediterranean are usually emitted as the 3+1 pattern. Not enough is known about the Mediterranean population to determine the connections between geographical areas. 3+1 remains the most common pattern, but a surprising variety of patterns was found, linking these animals to the situation present along the Hellenic trench. We used GAMs to establish seasonal variations to understand the movements of the species in the Ionian sea. Spring is the season richest in codas due to the greater presence of individuals. For the first time we demonstrate a relation between the pattern performed and the number of animals. This can be interpreted as an evidence of a different behavioural meaning.