31
2.8 Acoustic
Our acoustic studies with the Guiana dolphin began in the 1980s and after 10 years
of sampling, Monteiro-Filho and Monteiro (2001) described the specie’s sound repertoire, categorizing sounds in whistles, calls, clicks and gargle (emitted by calves;
Fig. 2.17), and even some complex sequences, as possible phrases. This was the first
study to assess sounds produced by the species in natural environment, as prior
studies only investigated Guiana dolphin in captivity (e.g. Caldwell and Caldwell
1970; Kamminga et al. 1993; Sauerland and Dehnhardt 1998).
Following the sound characterization for the species, studies have assessed the
influence of noise generated by vessels, concluding that anthropogenic noise forces
dolphins to raise the frequency range of the sounds used in social communication,
seeking a new acoustic niche (Rezende 2008; Fig. 2.18). Also in relation to the noise
produced by ships, Monteiro-Filho et al. (2008c) found that wooden boats and
inboard engines (fishing vessels) generate low intensity noise and in frequencies
below those used by dolphins. On the other hand, vessels with outboard engines
(fishing sports, passenger transport, and tourism) generate high intensity noise with
frequency equivalent to the lowest frequencies produced by dolphin, which may
cause the phenomenon of interference (Fig. 2.18).
Despite advances in knowledge of the sound emission of the species and the
context in which emission happen such as social, fishing, and nocturnal activities
(Monteiro-Filho and Monteiro 2001, 2008; Rodrigues 2003; Atem and MonteiroFilho 2006; Wanderley 2006; Oliveira et al. 2008; Rossi-Santos and Monteiro-Filho
2008), samples were specific and limited to 8 kHz and then to 20 kHz. Since such
frequencies did not allowed the interpretation of some features of dolphins’ acoustic
universe, from 2011, with availability of better equipment and systematic sampling,
we began evaluating sounds that reach sampling frequencies up to 48 kHz (Deconto
and Monteiro-Filho 2013, 2016; Fig. 2.19).
The most recent studies have advanced in relation to the characterization of the
sounds used in daytime and nighttime activities (Deconto and Monteiro-Filho
2016). The authors brought up a the new classification of dolphin sound emission in
the region, braking down the calls, originally described by Monteiro-Filho and
Monteiro (2001), into burst pulse sounds and low frequency narrow-band sounds
Fig. 2.16 The color patterns of calves skins are used to identify different ages classes. (a) A newborn shows a strong pinkish color the whole body. (b) F2 has an light pinkish color mainly at
dorsal fin and flanks. (c) In calves, the skin pigmentation is almost complete and only a small
region of dorsal fin remains pink, while the whole body is a dark-grey, like other adults (Photos:
Eric Medeiros)
2 Long-Term Monitoring of Dolphins in a Large Estuarine System of Southeastern…
2.8 Acoustic
Our acoustic studies with the Guiana dolphin began in the 1980s and after 10 years
of sampling, Monteiro-Filho and Monteiro (2001) described the specie’s sound repertoire, categorizing sounds in whistles, calls, clicks and gargle (emitted by calves;
Fig. 2.17), and even some complex sequences, as possible phrases. This was the first
study to assess sounds produced by the species in natural environment, as prior
studies only investigated Guiana dolphin in captivity (e.g. Caldwell and Caldwell
1970; Kamminga et al. 1993; Sauerland and Dehnhardt 1998).
Following the sound characterization for the species, studies have assessed the
influence of noise generated by vessels, concluding that anthropogenic noise forces
dolphins to raise the frequency range of the sounds used in social communication,
seeking a new acoustic niche (Rezende 2008; Fig. 2.18). Also in relation to the noise
produced by ships, Monteiro-Filho et al. (2008c) found that wooden boats and
inboard engines (fishing vessels) generate low intensity noise and in frequencies
below those used by dolphins. On the other hand, vessels with outboard engines
(fishing sports, passenger transport, and tourism) generate high intensity noise with
frequency equivalent to the lowest frequencies produced by dolphin, which may
cause the phenomenon of interference (Fig. 2.18).
Despite advances in knowledge of the sound emission of the species and the
context in which emission happen such as social, fishing, and nocturnal activities
(Monteiro-Filho and Monteiro 2001, 2008; Rodrigues 2003; Atem and MonteiroFilho 2006; Wanderley 2006; Oliveira et al. 2008; Rossi-Santos and Monteiro-Filho
2008), samples were specific and limited to 8 kHz and then to 20 kHz. Since such
frequencies did not allowed the interpretation of some features of dolphins’ acoustic
universe, from 2011, with availability of better equipment and systematic sampling,
we began evaluating sounds that reach sampling frequencies up to 48 kHz (Deconto
and Monteiro-Filho 2013, 2016; Fig. 2.19).
The most recent studies have advanced in relation to the characterization of the
sounds used in daytime and nighttime activities (Deconto and Monteiro-Filho
2016). The authors brought up a the new classification of dolphin sound emission in
the region, braking down the calls, originally described by Monteiro-Filho and
Monteiro (2001), into burst pulse sounds and low frequency narrow-band sounds
Fig. 2.16 The color patterns of calves skins are used to identify different ages classes. (a) A newborn shows a strong pinkish color the whole body. (b) F2 has an light pinkish color mainly at
dorsal fin and flanks. (c) In calves, the skin pigmentation is almost complete and only a small
region of dorsal fin remains pink, while the whole body is a dark-grey, like other adults (Photos:
Eric Medeiros)
2 Long-Term Monitoring of Dolphins in a Large Estuarine System of Southeastern…