326
Several studies indicate that S. guianensis have a high degree of fidelity to the
areas used by them, therefore areas that animals use several times or stay for a long
time are usually characterized as breeding grounds and feeding areas (eg Simão
et al. 2000; Gamboa-Poveda and May-Collado 2006; Araújo et al. 2007; RossiSantos et al. 2007; Wedekin 2007; Hardt et al. 2010; Oshima et al. 2010; RossiSantos et al. 2010; Batista et al. 2014).
Habitats of Guiana dolphins are close to the coast and their fidelity to these areas
make this species vulnerable to anthropogenic impacts, such as: whale watching
tours, boat traffic, buildings and coastal works, water pollution, driftnet fishing nets
and bycatch (eg Simões-Lopes and Ximenez 1990; Wedekin et al. 2002; Valle and
Melo 2006; Oliveira 2007; Di Benedito and Rosas 2008; Zappes et al. 2009;
Meirelles et al. 2010).
In this context, S. guianensis is currently one of the most studied cetacean species in Brazil and since 2014 is classified as “vulnerable” by Instituto Chico Mendes
de Conservação da Biodiversidade (ICMBio 2016). Despite this increase in research
efforts on this species, it is still classified as ‘insufficiently known’ species (deficient
data) by the International Union for Conservation of Nature and Natural Resources
(IUCN 2016).
Many issues still need to be elucidated in the relation of noises from anthropogenic sources and its implications to the life cycle of various aquatic animals. To
investigate this, studies are needed on the auditory sensitivity and acoustic repertoire
of species, the use of sounds in social, behavioral changes associated with noise,
temporary and permanent shifts in hearing thresholds and masking, when the anthropogenic noise, especially at high intensities occur simultaneously in the same frequency bands and time that the acoustic signals of marine animals (Clark et al. 2009).
Thus, this chapter presents a review of the Sotalia guianensis and describes the
repertoire of populations of this species recorded in three locations along the
Brazilian coast (Cananéia estuary – São Paulo State, Caravelas estuary – Bahia
State and Pipa beach – Rio Grande do Norte State) and compares them to anthropogenic noises recorded in these areas, bringing discussions on the acoustic ecology
of the Guiana dolphin and considerations on conservation.
13.1.2 Marine Acoustic Environment and Sound Propagation
The marine acoustic environment is composed by sounds that are in propagation in
an area and may undergo different processes (attenuation and degradation) according to the sound transmission related to oceanographic conditions, hydro and geoacoustics (Erbe et al. 2016). Substrate type, small changes in density gradients
mainly due to different temperatures, salinity and pressure determine the stratification and the sound distribution, which can become trapped in isobaric layers and
change their characteristics (eg Maglio et al. 2015).
Attenuation is a process in which the acoustic signal declines in intensity due
primarily to the spherical scattering effect, by the loss of energy during its transmisF. de Sousa Pais et al.
Several studies indicate that S. guianensis have a high degree of fidelity to the
areas used by them, therefore areas that animals use several times or stay for a long
time are usually characterized as breeding grounds and feeding areas (eg Simão
et al. 2000; Gamboa-Poveda and May-Collado 2006; Araújo et al. 2007; RossiSantos et al. 2007; Wedekin 2007; Hardt et al. 2010; Oshima et al. 2010; RossiSantos et al. 2010; Batista et al. 2014).
Habitats of Guiana dolphins are close to the coast and their fidelity to these areas
make this species vulnerable to anthropogenic impacts, such as: whale watching
tours, boat traffic, buildings and coastal works, water pollution, driftnet fishing nets
and bycatch (eg Simões-Lopes and Ximenez 1990; Wedekin et al. 2002; Valle and
Melo 2006; Oliveira 2007; Di Benedito and Rosas 2008; Zappes et al. 2009;
Meirelles et al. 2010).
In this context, S. guianensis is currently one of the most studied cetacean species in Brazil and since 2014 is classified as “vulnerable” by Instituto Chico Mendes
de Conservação da Biodiversidade (ICMBio 2016). Despite this increase in research
efforts on this species, it is still classified as ‘insufficiently known’ species (deficient
data) by the International Union for Conservation of Nature and Natural Resources
(IUCN 2016).
Many issues still need to be elucidated in the relation of noises from anthropogenic sources and its implications to the life cycle of various aquatic animals. To
investigate this, studies are needed on the auditory sensitivity and acoustic repertoire
of species, the use of sounds in social, behavioral changes associated with noise,
temporary and permanent shifts in hearing thresholds and masking, when the anthropogenic noise, especially at high intensities occur simultaneously in the same frequency bands and time that the acoustic signals of marine animals (Clark et al. 2009).
Thus, this chapter presents a review of the Sotalia guianensis and describes the
repertoire of populations of this species recorded in three locations along the
Brazilian coast (Cananéia estuary – São Paulo State, Caravelas estuary – Bahia
State and Pipa beach – Rio Grande do Norte State) and compares them to anthropogenic noises recorded in these areas, bringing discussions on the acoustic ecology
of the Guiana dolphin and considerations on conservation.
13.1.2 Marine Acoustic Environment and Sound Propagation
The marine acoustic environment is composed by sounds that are in propagation in
an area and may undergo different processes (attenuation and degradation) according to the sound transmission related to oceanographic conditions, hydro and geoacoustics (Erbe et al. 2016). Substrate type, small changes in density gradients
mainly due to different temperatures, salinity and pressure determine the stratification and the sound distribution, which can become trapped in isobaric layers and
change their characteristics (eg Maglio et al. 2015).
Attenuation is a process in which the acoustic signal declines in intensity due
primarily to the spherical scattering effect, by the loss of energy during its transmisF. de Sousa Pais et al.