Mapping underwater sound noise and assessing its sources by using a self-organizing maps method

Abstract

This study aims to provide an objective mapping of the underwater noise and its sources over an Adriatic coastal marine habitat by applying the self-organizing maps (SOM) method. Systematic sampling of sea ambient noise (SAN) was carried out at ten predefined acoustic stations between 2007 and 2009. Analyses of noise levels were performed for 1/3 octave band standard centered frequencies in terms of instantaneous sound pressure levels averaged over 300 s to calculate the equivalent continuous sound pressure levels. Data on vessels' presence, type, and distance from the monitoring stations were also collected at each acoustic station during the acoustic sampling. Altogether 69 noise surveys were introduced to the SOM predefined 2 × 2 array. The overall results of the analysis distinguished two dominant underwater soundscapes, associating them mainly to the seasonal changes in the nautical tourism and fishing activities within the study area and to the wind and wave action. The analysis identified recreational vessels as the dominant anthropogenic source of underwater noise, particularly during the tourist season. The method demonstrated to be an efficient tool in predicting the SAN levels based on the vessel distribution, indicating also the possibility of its wider implication for marine conservation.

A Study on the Impacts of Dolphin Watching as a Tourism Activity: Western Mauritius as Case Study

“…However, for the sake of this study, the Bottlenose dolphins are chosen as these are the species that mostly visit the Mauritian lagoon. The bottlenose dolphin is a widely distributed cetacean species with a range that includes both inshore and offshore waters [26]. According to the Mauritius Marine Conservation Society (MMCS), the bottlenose dolphins are vulnerable to many forms of human disturbance and this observation is an important premise to the current research.…”

“…More, they faced problems in terms of breathing rates; swimming directions, diving times, phonation rates [25]. Given that dolphins communicate by sound [24] and they are dependent on hearing to monitor and navigate in their environment [26], an uncontrolled marine environment with excessive activities disturbs their living. In fact, [23] observes that there are typically three levels of potential consequence of disturbances.…”

Dolphin changes in whistle structure with watercraft activity depends on their behavioral state

“…Many dolphin species rely on whistles for a number of behavioral activities; these signals are standardly described using a number of frequency components, which can be masked by watercraft noise (e.g., Morisaka et al, 2005;Sims et al, 2012;Rako et al, 2013b). Therefore, increasing boat traffic in dolphin habitat can potentially enhance the risk of limiting dolphin whistle detection by conspecifics, consequently affecting important dolphin behavioral activities for which whistle emission is essential.…”

“…The soundscape of dolphin habitats in coastal areas is largely dominated by watercraft noise (e.g., Haviland-Howell et al, 2007;Hildebrand, 2009;Sims et al, 2012;Rako et al, 2013b). Dolphins are known to respond to boat traffic and special attention has been given to whale-watching boat traffic due to its direct approach to the animals and extended periods of interaction.…”

Mapping of oceanographic properties along a middle Adriatic transect using Self-Organising Maps

“…The SOM was recently introduced to Adriatic oceanography as a useful tool for classifying patterns of different oceanographic parameters (Solidoro et al, 2007;Vilibi c et al, 2011;Mihanovi c et al, 2011;Rako et al, 2013;Kova c et al, 2014). In addition, SOM has been widely used in the global oceanographic community (Liu et al, 2006;Liu and Weisberg, 2011).…”