Monitoraggio acustico Del.Ta, Pelagie. 2006
Launched in 2003, the project aimed to carry out urgent actions for the conservation of the loggerhead turtle (Caretta caretta) and the bottlenose dolphin (Tursiops truncatus), two species protected by international regulations due to threats from human activities.
The main goal was to reduce interactions with fisheries, as well as the injuries or deaths resulting from them, particularly in Sicily.
The Pelagie Islands and the southern coast of Sicily were identified as priority areas to achieve these objectives.
As part of the Del.Ta project, Nauta was entrusted with the task of developing an underwater acoustic monitoring system, along with the related usage protocol and final acoustic analysis to determine the presence of bottlenose dolphins in the Pelagie Archipelago.
In particular, the study focused on the daily activities of bottlenose dolphins and their movements in relation to interactions with fishing gear and pingers (acoustic deterrent devices designed to keep dolphins away from nets and reduce bycatch), with the goal of identifying effective conservation solutions.
Passive acoustic methods were used: seabed recorders and hydrophones, specifically designed and built by Nauta, were employed to record and collect underwater sound data.
Nauta signed a legal agreement with the Regional Province of Agrigento, as a subcontractor, to carry out the specific tasks required by the Del.Ta project, including the development of instruments, the usage protocol, field operations, and the final acoustic analysis.
The underwater acoustic research activities took place between winter 2006 and winter 2007. Acoustic sensors and instruments were installed at the beginning of 2006 to allow continuous data collection throughout the year, which was then progressively analyzed.
The overall scientific supervision of the LIFE project was entrusted to Professor Cristina Giacoma of the University of Turin. The CIBRA (Interdisciplinary Centre for Bioacoustics and Environmental Research) at the University of Pavia supported the underwater acoustic research activities carried out by Nauta.
Professor Gianni Pavan, scientific director of the center, and his team have solid experience in acoustic monitoring methods. Nauta and CIBRA had already collaborated in the past, achieving significant results.
CIBRA hosted the equipment dedicated to storing and analyzing the collected data. A technical report was produced to describe the available solutions for this type of data collection.
To minimize interference between research activities and normal maritime operations of commercial vessels, the “seabed recorder” solution was adopted. Six recorders (+2 backups) were built and periodically deployed to collect acoustic data in a changing environment.
Data collection began in March 2006. Acoustic data were recorded using RASP recorders and then transferred to the centralized storage unit at the University of Pavia.
All data were accompanied by the local thermal profile (from 0 to -40 m), recorded both at deployment and recovery.
Acoustic data were collected in three frequency bands:
- 10 Hz – 16 kHz (compressed files),
- 10 Hz – 22 kHz (uncompressed files),
- 10 Hz – 46 kHz (uncompressed files).
The choice of band depended on whether the goal was to maximize recording duration, acoustic fidelity, or a balance between the two. Broadband recordings were made under favorable weather conditions, with recovery scheduled within 24 hours. Uncompressed recordings were planned for 72-hour fair-weather periods, while long-term compressed recordings were used during extended periods of stability. This logic was not rigid and could vary during field operations.
All data were archived at CIBRA – University of Pavia.
The acoustic analysis was carried out by Nauta, in collaboration with CIBRA.
The complete set of underwater recordings is available to the public and to other researchers upon request.
