334
Nowacek et al. 2007; Filla and Monteiro-Filho 2009), Increase in swimming speed
(Nowacek et al. 2001; Erbe 2002; Jahoda et al. 2003), changes in swimming direction (Nowacek et al. 2001; Lemon et al. 2006; Filla and Monteiro-Filho 2009),
changes of behavior (Miller et al. 2008; Stockin et al. 2008; Pirotta et al. 2015),
changes in group composition (Bejder et al. 1999; Filla and Monteiro-Filho 2009),
decrease in the distances between individuals (Nowacek et al. 2001; Valle and Melo
2006; Tosi and Ferreira 2009), changes in respiratory rate and breath timing (Janik
and Thompson 1996; Jahoda et al. 2003; Filla and Monteiro-Filho 2009; Hastie
et al. 2003; Tosi and Ferreira 2009).
Acoustic changes are intrinsically associated with the masking phenomenon,
when the anthropogenic noise overlaps the signals of animals (in the same frequency and greater intensity). According to Bain and Dahlheim (1994), noise generated by human activities can mask sound signals emitted by animals, forcing them
to spend more energy to communicate. Thus, according to review by Tyack and
Janik (2013), for greater efficiency to overcome ambient noise, the cetaceans can
change the intensity of the emitted signals, frequency, duration and repetition of
their signals.
Some authors claim that there is occurrence of habituation and/or acclimatization, referring to the body’s ability to change the perception of danger through experience, then decreased in behavioral response over time (Weilgart 2007; Wright and
Kuczaj 2007). But other authors believe it may be a mistake to say that there is
acclimatization only by finding the reduction of behavioral responses (Wright et al.
2007).
Anyway, behavioral change was observed in S. guianensis by Pereira et al.
(2007) in Baía Norte, Santa Catarina State, where during a period of 10 years in
contact with tour boats, reactions shifted from negative to neutral. It was also
observed decrease in behavioral responses by Izidoro and Le Pendu (2012) in southern Bahia State (Port of Ilhéus), which was described impartiality of Guiana dolphin
front of the approaches of the boats.
Behavioral responses observed in these cases potentially expose individuals to
physical injuries such as cuts, hearing damage and accidents with fishing nets
(Southall 2004; Zappes et al. 2010).
It is quite likely that aquatic animals are suffering high levels of stress in the
presence of noises even when showing minimal behavioral change (Wright and
Highfill 2007), as well as the apparent tolerance of noise does not imply that it is not
causing long-term impacts in animals (Weilgart 2007).
Clark et al. (2009) pointed out that the animals are exposed to sound sources less
dynamic, wider range of frequencies and constantly growing base level of noise in
the panorama of modern marine environment. In animal perspective, they are considerably different acoustic habitats, where it is more difficult to communicate when
compared to the environment in which they evolved.
F. de Sousa Pais et al.
Nowacek et al. 2007; Filla and Monteiro-Filho 2009), Increase in swimming speed
(Nowacek et al. 2001; Erbe 2002; Jahoda et al. 2003), changes in swimming direction (Nowacek et al. 2001; Lemon et al. 2006; Filla and Monteiro-Filho 2009),
changes of behavior (Miller et al. 2008; Stockin et al. 2008; Pirotta et al. 2015),
changes in group composition (Bejder et al. 1999; Filla and Monteiro-Filho 2009),
decrease in the distances between individuals (Nowacek et al. 2001; Valle and Melo
2006; Tosi and Ferreira 2009), changes in respiratory rate and breath timing (Janik
and Thompson 1996; Jahoda et al. 2003; Filla and Monteiro-Filho 2009; Hastie
et al. 2003; Tosi and Ferreira 2009).
Acoustic changes are intrinsically associated with the masking phenomenon,
when the anthropogenic noise overlaps the signals of animals (in the same frequency and greater intensity). According to Bain and Dahlheim (1994), noise generated by human activities can mask sound signals emitted by animals, forcing them
to spend more energy to communicate. Thus, according to review by Tyack and
Janik (2013), for greater efficiency to overcome ambient noise, the cetaceans can
change the intensity of the emitted signals, frequency, duration and repetition of
their signals.
Some authors claim that there is occurrence of habituation and/or acclimatization, referring to the body’s ability to change the perception of danger through experience, then decreased in behavioral response over time (Weilgart 2007; Wright and
Kuczaj 2007). But other authors believe it may be a mistake to say that there is
acclimatization only by finding the reduction of behavioral responses (Wright et al.
2007).
Anyway, behavioral change was observed in S. guianensis by Pereira et al.
(2007) in Baía Norte, Santa Catarina State, where during a period of 10 years in
contact with tour boats, reactions shifted from negative to neutral. It was also
observed decrease in behavioral responses by Izidoro and Le Pendu (2012) in southern Bahia State (Port of Ilhéus), which was described impartiality of Guiana dolphin
front of the approaches of the boats.
Behavioral responses observed in these cases potentially expose individuals to
physical injuries such as cuts, hearing damage and accidents with fishing nets
(Southall 2004; Zappes et al. 2010).
It is quite likely that aquatic animals are suffering high levels of stress in the
presence of noises even when showing minimal behavioral change (Wright and
Highfill 2007), as well as the apparent tolerance of noise does not imply that it is not
causing long-term impacts in animals (Weilgart 2007).
Clark et al. (2009) pointed out that the animals are exposed to sound sources less
dynamic, wider range of frequencies and constantly growing base level of noise in
the panorama of modern marine environment. In animal perspective, they are considerably different acoustic habitats, where it is more difficult to communicate when
compared to the environment in which they evolved.
F. de Sousa Pais et al.