499
17.8.4 Contaminants
Deposit of waste into the environment, especially in the water, is a growing problem
worldwide. Garbage has been found in the stomach contents of cetaceans found
dead on beaches, indicating that dolphins can and do swallow plastics, possibly
confusing the material with prey (e.g., squid) (Geise and Gomes 1988). In Argentina,
Denuncio et al. (2011) noted that franciscana dolphins in an estuary region had
more plastic debris in the stomach than those in the adjacent coastal region. Cunha
et al. (2014) also found plastic debris in franciscana dolphin carcasses recovered
from the coastal region outside of Babitonga Bay.
Contamination of the marine environment is partially due to the large contribution
of domestic and industrial effluents. Water contamination by chemical compounds is
a major concern, mainly due to cumulative effects. Organochlorines are one of the
major groups of pollutants that affect ecosystems due to persistence in the environment and toxicity to organisms (Clark 2001). For cetaceans, organochlorines are
linked to reproductive problems such as miscarriages, fetal malformations, hormonal
changes, and calf mortality, as well as skin problems. One study tested for organobromine compounds in liver samples from franciscana dolphins stranded along the
Brazilian coast, and found the highest polybrominated diphenyl ethers (PBDEs) concentrations in individuals from Babitonga Bay (Alonso et al. 2012).
17.9 Conclusion
Babitonga Bay is likely the only region of direct sympatry along the geographical
distribution of franciscana and Guiana dolphins. Although these species share the
same habitat and occupy a similar trophic level, minor differences in habitat use and
resource abundance probably contribute to the coexistence of these potentially competing species (Bearzi 2005). For example, Guiana dolphins are around twice the
size of franciscana dolphins, and this difference should produce higher energetic
demands. Although the two species share many prey in the area, their main prey
differ, and Guiana dolphins tend to prey upon larger species. The prey species that
are shared by dolphins are highly abundant in Babitonga Bay. Opportunistic feeding
behavior was also identified for sympatric populations of Stenella coeruleoalba and
Delphinus delphis, which prey on species that are most abundant (Das et al. 2000).
In Patagônia, Argentina, D. delphis and Lagenorynchus obscurus feed mainly on
the most abundant local fish species, which supports mixed-species aggregations in
the sympatric area (Romero et al. 2012). Differences in feeding strategy may also
explain the direct sympatry of D. delphis and T. truncatus in the Ionian Sea (Bruno
et al. 2004).
The sharing of prey species is minimized by different patterns of habitat use.
Although the home ranges of these dolphin populations strongly overlap, the core
areas differ and they never use the same areas at the same time. Effects of tidal
17 Behavior and Ecology of Endangered Species Living Together: Long-Term…
17.8.4 Contaminants
Deposit of waste into the environment, especially in the water, is a growing problem
worldwide. Garbage has been found in the stomach contents of cetaceans found
dead on beaches, indicating that dolphins can and do swallow plastics, possibly
confusing the material with prey (e.g., squid) (Geise and Gomes 1988). In Argentina,
Denuncio et al. (2011) noted that franciscana dolphins in an estuary region had
more plastic debris in the stomach than those in the adjacent coastal region. Cunha
et al. (2014) also found plastic debris in franciscana dolphin carcasses recovered
from the coastal region outside of Babitonga Bay.
Contamination of the marine environment is partially due to the large contribution
of domestic and industrial effluents. Water contamination by chemical compounds is
a major concern, mainly due to cumulative effects. Organochlorines are one of the
major groups of pollutants that affect ecosystems due to persistence in the environment and toxicity to organisms (Clark 2001). For cetaceans, organochlorines are
linked to reproductive problems such as miscarriages, fetal malformations, hormonal
changes, and calf mortality, as well as skin problems. One study tested for organobromine compounds in liver samples from franciscana dolphins stranded along the
Brazilian coast, and found the highest polybrominated diphenyl ethers (PBDEs) concentrations in individuals from Babitonga Bay (Alonso et al. 2012).
17.9 Conclusion
Babitonga Bay is likely the only region of direct sympatry along the geographical
distribution of franciscana and Guiana dolphins. Although these species share the
same habitat and occupy a similar trophic level, minor differences in habitat use and
resource abundance probably contribute to the coexistence of these potentially competing species (Bearzi 2005). For example, Guiana dolphins are around twice the
size of franciscana dolphins, and this difference should produce higher energetic
demands. Although the two species share many prey in the area, their main prey
differ, and Guiana dolphins tend to prey upon larger species. The prey species that
are shared by dolphins are highly abundant in Babitonga Bay. Opportunistic feeding
behavior was also identified for sympatric populations of Stenella coeruleoalba and
Delphinus delphis, which prey on species that are most abundant (Das et al. 2000).
In Patagônia, Argentina, D. delphis and Lagenorynchus obscurus feed mainly on
the most abundant local fish species, which supports mixed-species aggregations in
the sympatric area (Romero et al. 2012). Differences in feeding strategy may also
explain the direct sympatry of D. delphis and T. truncatus in the Ionian Sea (Bruno
et al. 2004).
The sharing of prey species is minimized by different patterns of habitat use.
Although the home ranges of these dolphin populations strongly overlap, the core
areas differ and they never use the same areas at the same time. Effects of tidal
17 Behavior and Ecology of Endangered Species Living Together: Long-Term…