26
authors verified that the generalized linear model with best fit presented salinity and
depth with a positive correlation with the Guiana dolphin occurrence in the region.
For a better understanding about the correlations between the species occurrence
and environmental factors, the former researcher is developing additive generalized
model to evaluate the use of habitat surrounding Cananéia Island, using several
environmental variables and fish captured in the cerco-fixo fishing gear (Godoy
et al. unpublished data). This study aims to evaluate anthropic interference in the
distribution of Guiana dolphins through a predictive modelling.
2.7 Behavior
The first activities carried out with this species in the Cananéia region were the
behavior studies. The naturalistic observations of the Guiana dolphin began early, in
the 1980s, and had as main objective to document and describe the various behaviors performed by these animals, even facing various difficulties at the time. Initially,
researchers did only land-based observations, since the geomorphological characteristics of the region favored this method of observation from some beaches.
However, over time, there was the need to expand the observations of behavior in
different areas of the estuary, thus scientists started to use different types of boats,
making it possible to obtain data from different perspectives.
The more than 600 h of observations of different behaviors carried out in
Cananéia estuary allowed a detailed description of the main behavioral events associated with different strategies, and measure them. The first set of descriptions of the
Guiana dolphin behaviors resulted from an effort of 10 years of observations,
detailed in the first doctoral thesis on cetaceans in Brazil (Monteiro-Filho 1991).
The author observed that the animals spend most of their time foraging activities,
and there may be small shifts to other areas suggesting heterogeneity in the distribution of food resources within the estuarine waters. Similarly, night observations also
have identified the same behavior performed and previously described for the day
periods (Atem and Monteiro-Filho 2006).
Monteiro-Filho (1991) described some basic behaviors such as swimming, shallow diving, deep diving, and rest, as well as a number of hunting strategies,
individuals and those carried out in groups. Fishing behaviors described for Guiana
dolphin range from more general behaviors such as pursuit (Fig. 2.12a), to more
complex behaviors such as pursuit with bubbles (Fig. 2.12b). Beside, there are
cooperative fishing activities, as circle formation (Fig. 2.12c), which may involve a
large number of individuals fishing cooperatively on a shoal.
The descriptions of such behaviors opened the door to further studies to identify
details in each behavior initially observed. Variations of these main behaviors
received emphasis and then compared with behavior of populations from other estuaries in order to identify possible variations due to changes in environmental characteristics (Domit 2006). Monteiro-Filho (1992) observed interspecific interactions
of the Guiana dolphin with at least five different species of marine and estuarine
birds commonly spotted in the region: boobies (Sula leucogaster, Boddaert, 1783),
E.L.A. Monteiro-Filho et al.
authors verified that the generalized linear model with best fit presented salinity and
depth with a positive correlation with the Guiana dolphin occurrence in the region.
For a better understanding about the correlations between the species occurrence
and environmental factors, the former researcher is developing additive generalized
model to evaluate the use of habitat surrounding Cananéia Island, using several
environmental variables and fish captured in the cerco-fixo fishing gear (Godoy
et al. unpublished data). This study aims to evaluate anthropic interference in the
distribution of Guiana dolphins through a predictive modelling.
2.7 Behavior
The first activities carried out with this species in the Cananéia region were the
behavior studies. The naturalistic observations of the Guiana dolphin began early, in
the 1980s, and had as main objective to document and describe the various behaviors performed by these animals, even facing various difficulties at the time. Initially,
researchers did only land-based observations, since the geomorphological characteristics of the region favored this method of observation from some beaches.
However, over time, there was the need to expand the observations of behavior in
different areas of the estuary, thus scientists started to use different types of boats,
making it possible to obtain data from different perspectives.
The more than 600 h of observations of different behaviors carried out in
Cananéia estuary allowed a detailed description of the main behavioral events associated with different strategies, and measure them. The first set of descriptions of the
Guiana dolphin behaviors resulted from an effort of 10 years of observations,
detailed in the first doctoral thesis on cetaceans in Brazil (Monteiro-Filho 1991).
The author observed that the animals spend most of their time foraging activities,
and there may be small shifts to other areas suggesting heterogeneity in the distribution of food resources within the estuarine waters. Similarly, night observations also
have identified the same behavior performed and previously described for the day
periods (Atem and Monteiro-Filho 2006).
Monteiro-Filho (1991) described some basic behaviors such as swimming, shallow diving, deep diving, and rest, as well as a number of hunting strategies,
individuals and those carried out in groups. Fishing behaviors described for Guiana
dolphin range from more general behaviors such as pursuit (Fig. 2.12a), to more
complex behaviors such as pursuit with bubbles (Fig. 2.12b). Beside, there are
cooperative fishing activities, as circle formation (Fig. 2.12c), which may involve a
large number of individuals fishing cooperatively on a shoal.
The descriptions of such behaviors opened the door to further studies to identify
details in each behavior initially observed. Variations of these main behaviors
received emphasis and then compared with behavior of populations from other estuaries in order to identify possible variations due to changes in environmental characteristics (Domit 2006). Monteiro-Filho (1992) observed interspecific interactions
of the Guiana dolphin with at least five different species of marine and estuarine
birds commonly spotted in the region: boobies (Sula leucogaster, Boddaert, 1783),
E.L.A. Monteiro-Filho et al.