327
sion. Degradation may occur through reverberation, amplitude fluctuations and different attenuations at different frequencies (Rabin et al. 2003).
Anthropogenic alterations in the natural environments such as topography, granulometry, salinity, temperature, and other factors, have the potential to change the
propagation characteristics of the acoustic signals by increasing the signals’ excess
of attenuation or degradation. Therefore, it’s extremely important to understand the
sound propagation in the specific study site before discussing the spectrum of the
soundscape (Erbe et al. 2016).
Experiments on mathematical models simulating the propagation of sound in the
ocean at different depths and bottom properties indicated that sound in shallow
waters (400 m) generally has intensity levels around 10–12 dB higher than in deep
waters (3000 m) and also has lower acoustic signal attenuation rate (less effect of
the spherical spreading) (Breitzke and Bohlen 2010).
In more consolidated substrates, i.e. superior hardness, the potential noise impact
is greater, as in hard bottoms multiple reflections at the water-substrate interface
overlap the refractions promoting sound reverberation. Therefore, an intense acoustic signal is potentially harmful especially in cases where the substrate is harder and
shallower, because the sound will remain with the same intensity (Breitzke and
Bohlen 2010).
A study of Ramos et al. (2012) on the spreading of tonal sounds reproduced in the
estuarine environment showed that low frequency signals (60–240 Hz) can be significantly attenuated (reaching up to one fifth of the intensity of the original signal)
in small depths sites (~ 5 m). Due to Lloyde mirrors’ effect (Urick 1983), based on
the reflection of the incident signals at the water-air interface, low frequency sounds
(typically generated by ships and large ships) can become very difficult to be heard,
hence increasing the risk of aquatic mammals collisions with ships (Gerstein 2002).
13.1.3 Anthropogenic Noise
The steady increase of human activities in oceanic and coastal areas have contributed to the increase of anthropogenic noise in the marine environment, making the
acoustic environments gradually more polluted (Andrew et al. 2002; Hildebrand
2009). Continental shelves are regions highly impacted by anthropogenic noise,
offshore mainly due to increased seismic and oil activity, and in the coastal area,
including bays and estuaries, which are impacted by noises from boats, worksites,
industrial and recreational activities (Rossi-Santos and Oliveira 2016).
13.1.3.1 Vessel Traffic Commercial
The traffic of large vessels (Fig. 13.5) every day across the oceans in frequent routes,
mainly in the Northern Hemisphere, creates very noisy acoustic environments, making it quite difficult for cetaceans’ communication to be effective especially for long
13 Anthropogenic Noise and Guiana Dolphins (Sotalia guianensis) in Brazil…
sion. Degradation may occur through reverberation, amplitude fluctuations and different attenuations at different frequencies (Rabin et al. 2003).
Anthropogenic alterations in the natural environments such as topography, granulometry, salinity, temperature, and other factors, have the potential to change the
propagation characteristics of the acoustic signals by increasing the signals’ excess
of attenuation or degradation. Therefore, it’s extremely important to understand the
sound propagation in the specific study site before discussing the spectrum of the
soundscape (Erbe et al. 2016).
Experiments on mathematical models simulating the propagation of sound in the
ocean at different depths and bottom properties indicated that sound in shallow
waters (400 m) generally has intensity levels around 10–12 dB higher than in deep
waters (3000 m) and also has lower acoustic signal attenuation rate (less effect of
the spherical spreading) (Breitzke and Bohlen 2010).
In more consolidated substrates, i.e. superior hardness, the potential noise impact
is greater, as in hard bottoms multiple reflections at the water-substrate interface
overlap the refractions promoting sound reverberation. Therefore, an intense acoustic signal is potentially harmful especially in cases where the substrate is harder and
shallower, because the sound will remain with the same intensity (Breitzke and
Bohlen 2010).
A study of Ramos et al. (2012) on the spreading of tonal sounds reproduced in the
estuarine environment showed that low frequency signals (60–240 Hz) can be significantly attenuated (reaching up to one fifth of the intensity of the original signal)
in small depths sites (~ 5 m). Due to Lloyde mirrors’ effect (Urick 1983), based on
the reflection of the incident signals at the water-air interface, low frequency sounds
(typically generated by ships and large ships) can become very difficult to be heard,
hence increasing the risk of aquatic mammals collisions with ships (Gerstein 2002).
13.1.3 Anthropogenic Noise
The steady increase of human activities in oceanic and coastal areas have contributed to the increase of anthropogenic noise in the marine environment, making the
acoustic environments gradually more polluted (Andrew et al. 2002; Hildebrand
2009). Continental shelves are regions highly impacted by anthropogenic noise,
offshore mainly due to increased seismic and oil activity, and in the coastal area,
including bays and estuaries, which are impacted by noises from boats, worksites,
industrial and recreational activities (Rossi-Santos and Oliveira 2016).
13.1.3.1 Vessel Traffic Commercial
The traffic of large vessels (Fig. 13.5) every day across the oceans in frequent routes,
mainly in the Northern Hemisphere, creates very noisy acoustic environments, making it quite difficult for cetaceans’ communication to be effective especially for long
13 Anthropogenic Noise and Guiana Dolphins (Sotalia guianensis) in Brazil…