Line of action:

Status:

Execution date:

The general objective of the study was to identify the impact of noise in Ibiza and Formentera and its correlation with the presence of cetaceans, mainly the bottlenose dolphin (Tursiops truncatus).

The specific objectives of the project have been the following:

• To identify optimal depth points for the instrumentation in the Natura 2000 Network of the Pityusic Islands and its recording protocol.
• To quantify the level of noise of anthropic origin on the coasts of Ibiza and Formentera over the course of a year.
• To assess the presence of bottlenose dolphins in the Natura 2000 Network of the Pitiusas Islands.
• Identify hourly, temporal and habitat use patterns by this species.
• To correlate the evolution of anthropic noise with the presence of the bottlenose dolphin.
• To learn about the role played by the marine protected areas of the Natura 2000 Network for the bottlenose dolphin.
• To assess the presence of other species of cetaceans in the area, such as the sperm whale (Physeter macrocephalus), fin whale (Balaenoptera physalus), common dolphin (Delphinus delphis), striped dolphin (Stenella coeruleoalba), pilot whale (Grampus griseus) and pilot whale (Globicephala melas).
• To make the problem of underwater noise known to the general public.

• Analysis of the noise/presence correlation of the bottlenose dolphin in the study area.
• Consensus with fishermen for the optimal location of anchorages in seven positions (5 in Ibiza and 2 in Formentera) within the Natura 2000 Network marine area surrounding Ibiza and Formentera.
• Anchoring of the network of acoustic devices in 7 Natura 2000 Network areas of the Pitiusas: Tagomago, Xamena, Illots de Ponent, Freus, Cala Saona, Sa Creu and “Don Pedro”.
• Design of the recording protocol.
• Analysis of acoustic files: quantification of noise level in the 1/3 octave bands of 63, 125, 250 and 500 Hz.
• Determination of the presence of bottlenose dolphins from the analysis of acoustic files.
• Signature whistle isolation, which has allowed the identification of 85 individuals of bottlenose dolphin.
• Statistical analysis of presence and connectivity between areas, assessing the percentage of individuals who are shared between areas and the time they reside in each locality.
• Quarterly downloads of acoustic files and replacement of drums, achieving a total of 195,118 acoustic files of the studio area recorded over the course of a year.
• Purchase management of acoustic recording devices.
• Dissemination and communication of the project through a specific portal of the project on its website, publications on its social networks, organization of informative conferences, participation in a podcast…

Thanks to the application of passive acoustics, the “Our Dolphins” project has evaluated the presence of dolphins, underwater noise and its correlation at one point in the port of Ibiza and six Natura 2000 Network areas of Ibiza and Formentera, important enclaves both for their large extension of the Natura Network and for being an important destination for nautical tourism in the Mediterranean.

Thanks to the sonoidentification by signature whistles, the population abundance of the bottlenose dolphin, the connectivity between Natura 2000 areas, the residence patterns and the fidelity to the area have been determined. It has been observed that dolphins prefer the south-southeast area of Ibiza (more than the north) and Formentera, and that some individuals have moved around the entire archipelago while most have been more faithful to certain areas of the coast. In addition, it has been found that between January and March there are three times more dolphins on the coast than in the months of July to October. It has also been estimated that the coastal population of bottlenose dolphins in the Pitiusas is approximately 108 dolphins (with a range of between 94 and 143 individuals). Finally, an important interconnection between the south-southeast area of Ibiza and the island of Formentera has been observed. These areas suffer greater nautical pressure, especially in summer, than the rest of the areas studied.

Likewise, by obtaining 195,118 acoustic files , underwater noise in the study areas has been characterized, detecting significant levels of noise pollution in some areas. It has been found that during the summer months in the Freus of Ibiza and Formentera there is 31 times more noise than in winter.

Finally, it has been found that there is an inverse relationship between the presence of bottlenose dolphins and total noise. With these results, it is affirmed that passive acoustics is postulated as a good tool for the monitoring of bottlenose dolphins and underwater noise, and the need for further research on these issues is demonstrated.

On the other hand, the project has fostered collaboration with the fishing sector in research work, agreeing with the fleet of Ibiza and Formentera on the anchorage points of the acoustic devices used. In addition, the results report has been sent by email to the following administrations: Subdirectorate General of Terrestrial and Marine Biodiversity; General Directorate of Biodiversity and Natural Spaces of the Government of the Balearic Islands; City Councils of the municipalities of Ibiza (Ibiza, Sant Josep, Sant Antoni and Santa Eulària City Councils) and the Formentera Island Council.