493
The availability and distribution of food resources are considered key factors
influencing habitat use for predators in both marine and terrestrial habitats (AcevedoGutiérrez and Parker 2000; Castro 2003; Hastie et al. 2004). Fish were sampled in
Babitonga Bay to evaluate potential relationships between diet (prey items) and
dolphin distributions (Fig. 17.15). Ninety-five teleost species were collected
between 2004 and 2005, of which 25 were considered part of the dolphin diet. The
central region of the bay accumulates the highest prey abundances, especially species of high importance for the franciscana dolphin that are abundant throughout the
year. These data support a hypothesis of generalist and opportunistic feeding behavior in franciscana dolphins, which appear to utilize whichever resource is most
abundant. Guiana dolphins also have generalist feeding behavior but select prey
with lower abundances in the bay, possibly because these species produce higher
energetic returns (Cremer 2007). Paitach (2015) found that prey were more abundant in low tide and that this factor constrains local spatial distributions.
Thirteen prey species were shared between franciscana and Guiana dolphins,
representing 62% of total franciscana prey species and 46% of Guiana dolphin prey
species (Cremer et al. 2011; Paitach 2015). Stable isotope analysis of δ
13
C and δ
15
N
in prey and predator tissue suggests that there is an overlap in the diet of these species, especially with respect to some preys (L. brevis, Diapterus rhombeus and S.
rastrifer) (Hardt et al. 2013).
17.8 Conservation Threats and Mortality
Coastal cetacean species are more vulnerable to impacts of human activities, primarily because coastal environments are intensively used by human populations.
Dolphin populations with restricted geographic ranges and strong dependence on
specific environmental characteristics are more vulnerable to habitat loss (Reeves
et al. 2003). Human activities such as ecotourism and associated noise pollution and
environmental degradation can promote changes in patterns of cetacean distribution
and habitat use (Richardson et al. 1995; Aguilar et al. 2000; Forcada 2002; Lusseau
2003). This is certainly the case for franciscana and Guiana dolphins in Babitonga
Bay (see section on Species Distribution and Habitat Use Patterns). Babitonga Bay
dolphins are exposed to many threats, and the consequences are not well understood. The negative impacts of human activities may occur directly (e.g., by causing
mortality or diseases), or indirectly when affect dolphin habitat.
Habitat loss will be one of the greatest threats to conservation in the coming
decades (Simberloff 1998; Groom and Vynne 2006). The reduction of the area of
occurrence for both dolphin species in Babitonga Bay is a clear indication of habitat
loss, caused mainly by impacts of human activities. Santos and Lacerda (1987) also
demonstrated abandonment of the Sado estuary in Portugal by T. truncatus, and
attributed it to significant habitat changes. The decline of T. truncatus populations
17 Behavior and Ecology of Endangered Species Living Together: Long-Term…
The availability and distribution of food resources are considered key factors
influencing habitat use for predators in both marine and terrestrial habitats (AcevedoGutiérrez and Parker 2000; Castro 2003; Hastie et al. 2004). Fish were sampled in
Babitonga Bay to evaluate potential relationships between diet (prey items) and
dolphin distributions (Fig. 17.15). Ninety-five teleost species were collected
between 2004 and 2005, of which 25 were considered part of the dolphin diet. The
central region of the bay accumulates the highest prey abundances, especially species of high importance for the franciscana dolphin that are abundant throughout the
year. These data support a hypothesis of generalist and opportunistic feeding behavior in franciscana dolphins, which appear to utilize whichever resource is most
abundant. Guiana dolphins also have generalist feeding behavior but select prey
with lower abundances in the bay, possibly because these species produce higher
energetic returns (Cremer 2007). Paitach (2015) found that prey were more abundant in low tide and that this factor constrains local spatial distributions.
Thirteen prey species were shared between franciscana and Guiana dolphins,
representing 62% of total franciscana prey species and 46% of Guiana dolphin prey
species (Cremer et al. 2011; Paitach 2015). Stable isotope analysis of δ
13
C and δ
15
N
in prey and predator tissue suggests that there is an overlap in the diet of these species, especially with respect to some preys (L. brevis, Diapterus rhombeus and S.
rastrifer) (Hardt et al. 2013).
17.8 Conservation Threats and Mortality
Coastal cetacean species are more vulnerable to impacts of human activities, primarily because coastal environments are intensively used by human populations.
Dolphin populations with restricted geographic ranges and strong dependence on
specific environmental characteristics are more vulnerable to habitat loss (Reeves
et al. 2003). Human activities such as ecotourism and associated noise pollution and
environmental degradation can promote changes in patterns of cetacean distribution
and habitat use (Richardson et al. 1995; Aguilar et al. 2000; Forcada 2002; Lusseau
2003). This is certainly the case for franciscana and Guiana dolphins in Babitonga
Bay (see section on Species Distribution and Habitat Use Patterns). Babitonga Bay
dolphins are exposed to many threats, and the consequences are not well understood. The negative impacts of human activities may occur directly (e.g., by causing
mortality or diseases), or indirectly when affect dolphin habitat.
Habitat loss will be one of the greatest threats to conservation in the coming
decades (Simberloff 1998; Groom and Vynne 2006). The reduction of the area of
occurrence for both dolphin species in Babitonga Bay is a clear indication of habitat
loss, caused mainly by impacts of human activities. Santos and Lacerda (1987) also
demonstrated abandonment of the Sado estuary in Portugal by T. truncatus, and
attributed it to significant habitat changes. The decline of T. truncatus populations
17 Behavior and Ecology of Endangered Species Living Together: Long-Term…