23
Beyond the importance of GLG in age estimation in S. guianensis, there is strong
evidence that the end of milk-feeding period is also registered. Rosas et al. (2003)
described an accessory layer deposited in the dentin between the neonatal layer and
first GLG as being possibly linked to the end of milk-feeding of the infants, which
varied between 6.7 and 10.3 months. According to the authors, the decrease of calcium caused by ablactation could reflect in a hipomineralized layer. Rosas and
Monteiro-Filho (2002) described the milk composition, where protein (9.5 g/100g)
and fat (17.1 g/100g) values were similar to those observed in other delphinids’ milk.
2.6 Population Parameters and Habitat Index
Monteiro-Filho (2000) conducted the first studies related to Guiana dolphin group
organization in Cananéia, defining three categories: individual (Fig. 2.8a), family
(Fig. 2.8b), and school (Fig. 2.8c). The family organization is the most commonly
seen in the study region, registered in more than 80% of the field observations
(Monteiro-Filho 2000). The basic structure is composed by a female and its calf, or
even by an adult, a female and its calf. For the first months after birth, while the calf
remains close to its mother (Fig. 2.9), the associated adult may aid the mother in feeding. Schools happen when there is an association of several families (Fig. 2.8c), which
can happen temporary (from 5 to 60 min) for feeding or displacement purposes.
Beside studies about social organization, it was also necessary to estimate dolphin density in the region. For cetaceans, researchers use diverse techniques to
assess population density such as census, mark-recapture method, land observations
and line transect. Bisi (2001) and Havukainen et al. (2011) made density estimates
for Cananéia region based on line transect, dividing the area in sectors and obtaining
values reaching 12.41 individuals/km
2
. The division of the area in sectors enabled
results to show a non-uniform use within sectors.
Fig. 2.7 (a) Sotalia guianensis teeth deposited at Instituto de Pesquisas Cananéia (IPeC) scientific
collection, municipality of Cananéia, State of São Paulo, Brazil. (b) Photomicrography of apical
region of Sotalia guianensis teeth, cut at 30 μm and colored with Harris’ Hematoxylin. LN
Neonatal line, 1° GLG – first growth layer group referring to the first year of life, 2° GLG second
growth layer group referring to an incomplete second year of life (Photos: Rebeca P. Wanderley)
2 Long-Term Monitoring of Dolphins in a Large Estuarine System of Southeastern…
Beyond the importance of GLG in age estimation in S. guianensis, there is strong
evidence that the end of milk-feeding period is also registered. Rosas et al. (2003)
described an accessory layer deposited in the dentin between the neonatal layer and
first GLG as being possibly linked to the end of milk-feeding of the infants, which
varied between 6.7 and 10.3 months. According to the authors, the decrease of calcium caused by ablactation could reflect in a hipomineralized layer. Rosas and
Monteiro-Filho (2002) described the milk composition, where protein (9.5 g/100g)
and fat (17.1 g/100g) values were similar to those observed in other delphinids’ milk.
2.6 Population Parameters and Habitat Index
Monteiro-Filho (2000) conducted the first studies related to Guiana dolphin group
organization in Cananéia, defining three categories: individual (Fig. 2.8a), family
(Fig. 2.8b), and school (Fig. 2.8c). The family organization is the most commonly
seen in the study region, registered in more than 80% of the field observations
(Monteiro-Filho 2000). The basic structure is composed by a female and its calf, or
even by an adult, a female and its calf. For the first months after birth, while the calf
remains close to its mother (Fig. 2.9), the associated adult may aid the mother in feeding. Schools happen when there is an association of several families (Fig. 2.8c), which
can happen temporary (from 5 to 60 min) for feeding or displacement purposes.
Beside studies about social organization, it was also necessary to estimate dolphin density in the region. For cetaceans, researchers use diverse techniques to
assess population density such as census, mark-recapture method, land observations
and line transect. Bisi (2001) and Havukainen et al. (2011) made density estimates
for Cananéia region based on line transect, dividing the area in sectors and obtaining
values reaching 12.41 individuals/km
2
. The division of the area in sectors enabled
results to show a non-uniform use within sectors.
Fig. 2.7 (a) Sotalia guianensis teeth deposited at Instituto de Pesquisas Cananéia (IPeC) scientific
collection, municipality of Cananéia, State of São Paulo, Brazil. (b) Photomicrography of apical
region of Sotalia guianensis teeth, cut at 30 μm and colored with Harris’ Hematoxylin. LN
Neonatal line, 1° GLG – first growth layer group referring to the first year of life, 2° GLG second
growth layer group referring to an incomplete second year of life (Photos: Rebeca P. Wanderley)
2 Long-Term Monitoring of Dolphins in a Large Estuarine System of Southeastern…