LIFE HISTORY AND ECOLOGY OF FRANCISCANA, PONTOPORIA BLAINVILLEI (CETACEA, PONTOPORIIDAE) - Biology, Evolution and Conservation of River Dolphins Within South America and Asia - page 313

The higher reproductive potential of females from Rio Grande do Sul/Uruguay area might be
due to a density-dependent response to several years of incidental mortality in fisheries.
Franciscanas from this area have experienced high levels of bycatch for a long period
(Praderi, 1997; Secchi et al., 2003b). Although density-dependent response to bycatch has yet
to be documented in franciscana, the possibility that animals from Rio Grande do
Sul/Uruguay have been responding to high levels of bycatch by reducing the age at first
reproduction and/or by increasing reproductive rates cannot be ruled out.
The lower estimated growth rate for the population from Santa Catarina/Paraná/São
Paulo States is possibly due to a combination of intrinsically low reproductive potential and
poor parameter estimation. Some parameters for this area were obtained from small sample
sizes. For example, Rosas and Monteiro Filho (2002) suggest that franciscanas are sexually
mature between 4 and 5 years of age and reproduce biannually based on a sample of only six
mature animals. Franciscanas from adjacent areas have much higher reproductive potential
(Di Beneditto & Ramos, 2001; Danilewicz et al., 2000; Danilewicz, 2003). If the much lower
reproductive potential is not an artifact of poor estimation, then a compensatory higher
survival could be expected. If this is the case, then the population growth rate for this area and
for Argentina as well could be underestimated as the survival rates estimated with data from
the Rio Grande do Sul/Uruguay were assumed to be the same for these populations. Given
this uncertainty, it is recommended that more precise estimates on reproductive parameters
are obtained for those areas. Despite geographic variation and parameter uncertainties, the
estimated growth rate for the species is within the range of likely growth rate for small
cetaceans ( e.g. Reilly & Barlow, 1986; Slooten & Lad, 1991; Stolen & Barlow, 2003).

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[2]

Andrade, A. L. V., Pinedo, M. C. & Pereira Jr, J. (1997). The gastrointestinal helminths
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[3] Azevedo, A. F., Fragoso, A. B. L., Lailson-Brito Jr., J., & Cunha, H. A. (2002).

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[4] Aznar, F. J., Balbuena, J. A. & Raga, J. A. (1994). Helminth communities of

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[6] Aznar, F. J., Balbuena, J. A., Bush, A. O. & Raga, J. A. (1997). Ontogenetic habitat

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