The Blue World Institute researchers have published a series of scientific papers in which they study the effects of noise produced by boats on our coastal population of bottlenose dolphins in the Lošinj/Kvarnerić region. Sound is of particular importance for bottlenose dolphins as they use it for navigation, communication and foraging. Understanding the impact that noise has on them is essential to help developing better management and conservation measures.
Dr. Nikolina Rako Gospić, the Blue World Institute Science director said “In the paper we published in 2013 our results showed that the sea ambient noise variations related to intense recreational boating led to dolphin avoidance of the areas with increased noiselevels. Such behaviour was a response to a reduced range of communication for bottlenose dolphins and a decrease of the signal-to-noise ratio in the presence of high boat traffic.”
Bottlenose dolphins vocalise almost all of the time, but the intense vocalisation occurs during different social activities when dolphins increase their vocalisation to establish contacts with other animals in the group. Of particular importance is vocalisation between mother and calf that helps establish a close bond but is also used to teach or warn young dolphin. Very intensive vocalisation also occurs within bottlenose dolphin groups during group foraging as dolphins rely on sound to be able to coordinate their joint actions and to enhance their hunting success.
The most recent research of the Blue World Institute was focused on dolphin vocalisation and change that noise has on the way dolphins are modifying it in the noisy environment. The results of the new paper, which has just been published in Marine Pollution Bulletin, show that dolphins significantly change their whistles when there is a lot of noise in the environment.
Dr Rako Gospić says: “Of particular interest is that in the presence of boats dolphins produced whistles of significantly higher frequencies. Such behaviour was most obvious during foraging and socializing activities when in tense communication among the co-members within a group occurs.”
What researchers have found out is that changes in dolphin social calls indicate that in order to increase the possibility of being heard by other animals dolphins had to modify their acoustic signals. Such alteration of dolphin acoustic behaviour in the presence of boats is most likely a response to compensate for masking of their regular calls.
Dr. Marta Picciulin, co-author of the research says: “What happens in the noisy environment is that sounds produced by dolphins are becoming cove red or “masked”
by the noise produced by boats. As boats produce noise mostly in low frequency range, in order to make their calls any useful and to be able to continue using sound dolphins had to increase the frequency of their calls”
Changes in vocalisation behaviour indicate that noise in the environment is yet another stressor in the environment that coastal bottlenose dolphins are exposed to. Although we cannot currently quantify the impact it has on them, we can expect that it also causes the higher energy requirements. But getting more food in the environment that is overfished, may simply become impossible. This is of particular importance for sensitive females with calves as the food intake of mother’s increases during the weaning period also due to milk production and care for the calf. Underestimating the long term impact that noise may have on the breeding success and health of the resident bottlenose dolphins may render
the Cres and Lošinj NATURA 2000 site for the bottlenose dolphins obsolete.
For more information or copy of the papers contact the author of the study:
Dr. Nikolina Rako Gospić, Science director
Blue World Institute of Marine Research and Conservation
Kaštel 24, HR-51551 Veli Lošinj, Croatia
T: +385 51 604666 F: +385 51 604668
Rako Gospić. N., Picciulin, M., (2016) Changes in whistle structure of resident bottlenose dolphins in relation to underwater noise and boat traffic, Marine Pollution Bulletin,
Rako, N., Fortuna, C.M., Holcer, D., Mackelworth, P.C., Nimak-Wood, M., Pleslić, G.,
Sebastianutto, L., Vilibić, I., Wiemann, A., Picciulin, M., 2013. Leisure boating noise
as a trigger for the displacement of the bottlenose dolphins of the Cres-Lošinj archipelago (northern Adriatic Sea, Croatia). Marine Pollution Bulletin 68 (1-2), 77-84.
Picciulin M., Sebastianutto L., Fortuna C.M., Mackelworth C.P., Holcer D. I Rako N. (2013) Are the 1/3 Octave 63 and 125 Band Noise Levels Predictive of Vessel ? The Case of Cres-Lošinj Archipelago (Northern Adriatic Sea, Croatia). In: Third International Conference on the Effects of Noise on Aquatic Life, Budapest, Hungary.
Rako N., Picciulin M., Vilibić I. i Fortuna C.M. (2013) Spatial and temporal variability
of sea ambient noise as an anthropogenic pressure index: the case of the Cres-Lošinj archipelago, Croatia. Journal of the Marine Biological Association of the United Kingdom 93, 27-36.
Rako N., Picciulin M., Mackelworth C.P., Holcer D. i Fortuna C.M. (2012) Long-term
monitoring of anthropogenic noise and its relationship to bottlenose dolphin (Tursiops
truncatus) distribution in the Cres-Lošinj archipelago, northern Adriatic, Croatia. In:
The Effects of Noise on Aquatic Life (eds. by Popper AN I Hawkins A), pp. 323-325.
Springer, Dordrecht.
Rako N., Picciulin M., Fortuna C.M. i Holcer D. (2008) Il rumore ambientale marino come indicatore dell’impatto antropico sulla distribuzione del tursiope (Tursiops truncatus) nell’area marina protetta di Lussino (Croazia). In: Gli effetti delle attività antropiche in mare, sulla costa e nell’entroterra sulla biodive rsità dell’Alto Adriatico. Institute of the Republic of Slovenia for Nature Conservation, Piran, Slovenia.