211
8.4 Discussion
In this work we found that tail up behavior varied in frequency according to the
depth. It is probable that the narrow continental shelf is influencing this fact, once
circa 60% of the sightings for humpback whales in this area are situated in waters
of 35–55 m deep (Rossi-Santos et al. 2008).
Seven different species of dolphins had been sighted during the research conducted through the coast of the North shore of Bahia, between the years 2001 and
2006. Al these species are confirmed by literature (eg. Pinedo et al. 1992; Hetzel and
Lodi 1993), except for the Feresa attenuata that had its first record of sighting for
the Brazilian coast (Rossi-Santos et al. 2006b) and Stenella frontalis that had its first
record of sighting for the coast of Bahia State. Species of both coastal and pelagic
habits had been sighted during the study, fact that could be associated with oceanographic characteristic, such as the narrow continental platform, with about 7 nautical miles, in the study area (DHN 1995).
The bottlenose dolphin, T. truncatus, was the most frequent species during the
period of the study. It is the most common dolphin species and more studied in all
the oceans (e.g. Leatherwood and Reeves 1983; Bearzi 2005; Blasi and Boitani
2012). In Brazil, despite it is not the most studied species, the dolphin have been
increasingly investigated (eg., Sampaio and Reis 1998; Simões-Lopes and Fábian
1999; Silva et al. 2002; Baracho et al. 2005; Rossi-Santos et al. 2006a; Baracho
et al. 2008; Lodi et al. 2008, Carvalho and Rossi-Santos 2011; Tardin et al. 2013).
Although the majority of the studies are about coastal populations, the species had
being sighted in oceanic waters (Sampaio and Reis 1998; Cremer et al. 2002; Silva
et al. 2002; Caon and Ott 2004; Baracho et al. 2005; Baracho et al. 2008; Carvalho
and Rossi-Santos, 2011).
Group size varied between 1 and 30 individuals. T. truncatus is found generally
in relatively small groups of 1–20 animals (Shane et al. 1986; Bastida et al. 2007;
Carvalho and Rossi-Santos 2011; Lodi and Monteiro-Neto 2012). An notable exception is mentioned for T. aduncus in the South Africa, where the size of the group
varied of 3–1000 and the average of animals for group was of 140 (Saayman and
Tayler 1973).
Table 8.2 Depth variation (meters), sea state variation (Beaufort scale) and variation of wind
intensity (nodes) between the years 2001 and 2006
Species
Δ Depth
variation
Δ Sea state
variation
Δ Variation of wind
intensity
Tursiops truncatus
10–50
0–4
05–15
Sotalia guianensis
04–60
0–3
03–12
Steno bredanensis
27–45
1–5
09–16
Stenella clymene
42–121
2–4
09–14
Feresa attenuata
97–200
1
08
Peponocephala electra
51
1
09
Stenella frontalis
150
1
16
8 Opportunistic Sightings of Dolphins (MAMMALIA, CETACEA, DELPHINIDAE)…
8.4 Discussion
In this work we found that tail up behavior varied in frequency according to the
depth. It is probable that the narrow continental shelf is influencing this fact, once
circa 60% of the sightings for humpback whales in this area are situated in waters
of 35–55 m deep (Rossi-Santos et al. 2008).
Seven different species of dolphins had been sighted during the research conducted through the coast of the North shore of Bahia, between the years 2001 and
2006. Al these species are confirmed by literature (eg. Pinedo et al. 1992; Hetzel and
Lodi 1993), except for the Feresa attenuata that had its first record of sighting for
the Brazilian coast (Rossi-Santos et al. 2006b) and Stenella frontalis that had its first
record of sighting for the coast of Bahia State. Species of both coastal and pelagic
habits had been sighted during the study, fact that could be associated with oceanographic characteristic, such as the narrow continental platform, with about 7 nautical miles, in the study area (DHN 1995).
The bottlenose dolphin, T. truncatus, was the most frequent species during the
period of the study. It is the most common dolphin species and more studied in all
the oceans (e.g. Leatherwood and Reeves 1983; Bearzi 2005; Blasi and Boitani
2012). In Brazil, despite it is not the most studied species, the dolphin have been
increasingly investigated (eg., Sampaio and Reis 1998; Simões-Lopes and Fábian
1999; Silva et al. 2002; Baracho et al. 2005; Rossi-Santos et al. 2006a; Baracho
et al. 2008; Lodi et al. 2008, Carvalho and Rossi-Santos 2011; Tardin et al. 2013).
Although the majority of the studies are about coastal populations, the species had
being sighted in oceanic waters (Sampaio and Reis 1998; Cremer et al. 2002; Silva
et al. 2002; Caon and Ott 2004; Baracho et al. 2005; Baracho et al. 2008; Carvalho
and Rossi-Santos, 2011).
Group size varied between 1 and 30 individuals. T. truncatus is found generally
in relatively small groups of 1–20 animals (Shane et al. 1986; Bastida et al. 2007;
Carvalho and Rossi-Santos 2011; Lodi and Monteiro-Neto 2012). An notable exception is mentioned for T. aduncus in the South Africa, where the size of the group
varied of 3–1000 and the average of animals for group was of 140 (Saayman and
Tayler 1973).
Table 8.2 Depth variation (meters), sea state variation (Beaufort scale) and variation of wind
intensity (nodes) between the years 2001 and 2006
Species
Δ Depth
variation
Δ Sea state
variation
Δ Variation of wind
intensity
Tursiops truncatus
10–50
0–4
05–15
Sotalia guianensis
04–60
0–3
03–12
Steno bredanensis
27–45
1–5
09–16
Stenella clymene
42–121
2–4
09–14
Feresa attenuata
97–200
1
08
Peponocephala electra
51
1
09
Stenella frontalis
150
1
16
8 Opportunistic Sightings of Dolphins (MAMMALIA, CETACEA, DELPHINIDAE)…