63
greater pressure from this activity. He also found the occurrence of groups with
calves peaked during September and October and groups without calves and competitive groups decreased towards the end of the breeding season (September–
October), when compared with the beginning of the season (July–August). This can
be explained by the fact that these whales’ migration is age structured, females with
new calves being the final cohort (Chittleborough 1965; Dawbin 1966), so in the
later stages of the whale-watching season the activity concentrates on females with
calves.
However, for boat interactions to affect the vital rates of individual baleen whales
in Praia do Forte, they would have to significantly disrupt the breeding or nursing
process. In the case of females with calves, any lost nursing opportunities or
decreased lactation due to the energy cost of displacement in response to whalewatching disturbance, can be easily compensated at a later moment (Lusseau 2014),
since the legislation only allows 30 min of observation and the number of vessels is
low. Additionally, humpback whales in the area are able to avoid disturbance from
whale-watching vessel approach because they have plenty of alternative sites to go
to, since the whale-watching activity currently operates over a limited area (Fig. 3.1).
However, calf growth tends to peak towards the end of the breeding season
(Whitehead and Payne 1981), time during which calves need the most energetic
investment from their mothers in order to increase lactation (Lusseau 2014), coinciding with a peak in the proportion of time females spend resting (Thomas and
Taber 1984), the activity state in which nursing takes place.
As such, this concentration of whale-watching interactions with female and calf
groups towards the end of the breeding season, a critical period in calf development,
could compromise calf growth, leading to increased mortality or decreased survival
probability as they undertake the long migration to the feeding grounds (McMahon
et al. 2000).
However, the northern coast of Bahia is not as important a breeding ground as the
Abrolhos Bank, in southern Bahia, since a smaller proportion of individuals
observed is of new-born calves (Pacheco de Godoy et al. 2005; Lunardi et al. 2008).
Additionally, the northern coast is the area along Bahia that shows the smallest
annual population growth rate (Wedekin 2011). As such, the whale-watching activity is less likely to impact calf birth or survival rates here than in Abrolhos, which is
one of the main ways in which whale-watching can have any long-term impacts on
cetacean populations (Christiansen and Lusseau 2014). Additionally, data collected
on-board whale-watching vessels for over 10 years in Praia do Forte show an
increase in numbers of groups with calves sighted in the region, also a consequence
of population growth, suggesting the activity is not having a negative impact on
calving rate (Cipolotti 2013).
Another noteworthy aspect is that the whales show low site fidelity and occupancy rates on the north coast of Bahia, remaining in the same area for an average
5.5 days only, contrasting with 15 days in the Abrolhos Bank (Baracho-Neto et al.
2012). There are also significant differences in the concentration and distribution
patterns of different social groups between the northern coast of Bahia and Abrolhos.
Although these two regions comprise distinct concentrations of humpback whales,
3 An Integrated Framework to Assess the Carrying Capacity…
greater pressure from this activity. He also found the occurrence of groups with
calves peaked during September and October and groups without calves and competitive groups decreased towards the end of the breeding season (September–
October), when compared with the beginning of the season (July–August). This can
be explained by the fact that these whales’ migration is age structured, females with
new calves being the final cohort (Chittleborough 1965; Dawbin 1966), so in the
later stages of the whale-watching season the activity concentrates on females with
calves.
However, for boat interactions to affect the vital rates of individual baleen whales
in Praia do Forte, they would have to significantly disrupt the breeding or nursing
process. In the case of females with calves, any lost nursing opportunities or
decreased lactation due to the energy cost of displacement in response to whalewatching disturbance, can be easily compensated at a later moment (Lusseau 2014),
since the legislation only allows 30 min of observation and the number of vessels is
low. Additionally, humpback whales in the area are able to avoid disturbance from
whale-watching vessel approach because they have plenty of alternative sites to go
to, since the whale-watching activity currently operates over a limited area (Fig. 3.1).
However, calf growth tends to peak towards the end of the breeding season
(Whitehead and Payne 1981), time during which calves need the most energetic
investment from their mothers in order to increase lactation (Lusseau 2014), coinciding with a peak in the proportion of time females spend resting (Thomas and
Taber 1984), the activity state in which nursing takes place.
As such, this concentration of whale-watching interactions with female and calf
groups towards the end of the breeding season, a critical period in calf development,
could compromise calf growth, leading to increased mortality or decreased survival
probability as they undertake the long migration to the feeding grounds (McMahon
et al. 2000).
However, the northern coast of Bahia is not as important a breeding ground as the
Abrolhos Bank, in southern Bahia, since a smaller proportion of individuals
observed is of new-born calves (Pacheco de Godoy et al. 2005; Lunardi et al. 2008).
Additionally, the northern coast is the area along Bahia that shows the smallest
annual population growth rate (Wedekin 2011). As such, the whale-watching activity is less likely to impact calf birth or survival rates here than in Abrolhos, which is
one of the main ways in which whale-watching can have any long-term impacts on
cetacean populations (Christiansen and Lusseau 2014). Additionally, data collected
on-board whale-watching vessels for over 10 years in Praia do Forte show an
increase in numbers of groups with calves sighted in the region, also a consequence
of population growth, suggesting the activity is not having a negative impact on
calving rate (Cipolotti 2013).
Another noteworthy aspect is that the whales show low site fidelity and occupancy rates on the north coast of Bahia, remaining in the same area for an average
5.5 days only, contrasting with 15 days in the Abrolhos Bank (Baracho-Neto et al.
2012). There are also significant differences in the concentration and distribution
patterns of different social groups between the northern coast of Bahia and Abrolhos.
Although these two regions comprise distinct concentrations of humpback whales,
3 An Integrated Framework to Assess the Carrying Capacity…