To apply the passive acoustic methodology to the monitoring of most odontocete species, information on the time that animals spend vocalising should be acquired and knowledge on vocal activity linked to different behavioural context should be improved.During the summers 2009 and 2010, 63 surveys have been conducted in the Ionian Sea in order to investigate the changes of vocalisations rate of striped dolphin in relation to group size and behaviour. 80 hours were spent monitoring, 22 collecting behavioural data and 5 recording vocalisations. The 48% (1.13 hours) of the total 2.33 hours of recordings synchronised with behavioural data were of silent animals. Among the recorded vocalisations the most frequent were clicks, followed by whistles. Statistical analysis (Rho Spearman’s Test) highlighted a negative correlation among the number of animals and the seconds of silence (P< 0.05). The number of animals was then classified in 4 categories: 1) 1-5; 2) 6-9; 3) 10-15; 4) 20-30. Statistical analysis (Kruscall-Wallis) showed that the seconds of silence were significantly greater (P< 0.005) for the first category, decreasing for the second, minimum for the third and increasing again for the forth. The most frequent states (normal swim, rafting and sharking) and events (leap, tail slap and bow) were used for investigating correlation among behaviours and vocal activity. The Rho Spearman’s Test highlighted that the duration of normal swim was positively correlated with seconds of silence (P< 0.05), while the frequency of all events showed a negative correlation (P< 0.05). The results of this study highlight that further passive acoustic data collected in the area should be adjusted taking into account that the 48% of the timeanimals are not vocalising. Finally, this study suggests that duringnormal swim communication is probably linked to other senses than acoustic.
To be silent or to communicate? Analysis of the Mediterranean striped dolphin (Stenella coeruleoalba) acoustic behaviour in order to improve passive acoustic monitoring
GIACOMA, Cristina;PAPALE, ELENA
2011-01-01
Abstract
To apply the passive acoustic methodology to the monitoring of most odontocete species, information on the time that animals spend vocalising should be acquired and knowledge on vocal activity linked to different behavioural context should be improved.During the summers 2009 and 2010, 63 surveys have been conducted in the Ionian Sea in order to investigate the changes of vocalisations rate of striped dolphin in relation to group size and behaviour. 80 hours were spent monitoring, 22 collecting behavioural data and 5 recording vocalisations. The 48% (1.13 hours) of the total 2.33 hours of recordings synchronised with behavioural data were of silent animals. Among the recorded vocalisations the most frequent were clicks, followed by whistles. Statistical analysis (Rho Spearman’s Test) highlighted a negative correlation among the number of animals and the seconds of silence (P< 0.05). The number of animals was then classified in 4 categories: 1) 1-5; 2) 6-9; 3) 10-15; 4) 20-30. Statistical analysis (Kruscall-Wallis) showed that the seconds of silence were significantly greater (P< 0.005) for the first category, decreasing for the second, minimum for the third and increasing again for the forth. The most frequent states (normal swim, rafting and sharking) and events (leap, tail slap and bow) were used for investigating correlation among behaviours and vocal activity. The Rho Spearman’s Test highlighted that the duration of normal swim was positively correlated with seconds of silence (P< 0.05), while the frequency of all events showed a negative correlation (P< 0.05). The results of this study highlight that further passive acoustic data collected in the area should be adjusted taking into account that the 48% of the timeanimals are not vocalising. Finally, this study suggests that duringnormal swim communication is probably linked to other senses than acoustic.
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