| Multidisciplinary analyses of genetic and environmental data for cetacean population structure studies allow investigating hypotheses of environmental drivers to dispersal, and provide valuable information for the conservation of these species. This dissertation combines microsatellite and mitochondrial DNA (mtDNA) data of coastal cetaceans with remote sensing oceanographic information to assess the degree of overlap between genetic and environmental breaks, and provide recommendations for the designation of cetacean management units associated to important geographical areas for distinct populations. Genetic and demographic data are used to evaluate potential demographic and genetic impacts of by-catch to cetacean species, and species distribution data to evaluate the appropriateness of existing Marine Protected Areas in South America for the conservation of local cetaceans.Issues of environmental agents to population structure are comparatively explored in two coastal cetacean species that inhabit different ocean basins. Chapter 1 evaluates the regional population structure of Franciscana dolphins (Pontoporia blainvillei) through a population genetic analysis using mtDNA data, covering the entire species distribution in the Western South Atlantic. The results show significant population structure between dolphins occurring in Brazilian, Uruguayan and Argentinean waters, and suggest further genetic structure within the groups of animals collected in Argentina. Chapter 2 narrows the spatial scale of analysis focusing on the Argentinean coastline, includes previously unsampled localities, doubles the sample size, and incorporates 12 microsatellite markers into the previous genetic dataset. Using a combination of frequency, likelihood and Bayesian analytical methods, this chapter supports the previously hinted genetic patterns of finer-scale population structure within Argentina. Moreover, this chapter couples the genetic data with remote sensing oceanographic information and shows a concordant spatial arrangement of the genetic and environmental breaks. In addition, this evidence suggests that a mechanism termed here "isolation by environmental distance" may explain some of the observed patterns. Analogous issues of environmental and population structure are evaluated for humpback dolphins in the Western Indian Ocean in Chapter 3. Contrasting mtDNA sequence data with a suite of remotely driven oceanographic variables, the results of this analysis show concordant regional oceanographic breaks to the strong and highly significant genetic structure, and suggest that surface currents and ocean color properties may play a significant role in dispersal of humpback dolphins in this region.Addressing relevant aspects of cetacean conservation, an evaluation of genetic and demographic impacts of by-catch to Franciscana dolphins is provided in Chapter 4. Through an analysis of relatedness between dolphins entangled in fishing gear it is demonstrated that, in addition to removing large numbers of individuals from their populations, by-catch also impacts mother-calf associations and reproductive pairs, exacerbating the process of population decline. Finally, in order to evaluate the suitability of the existing Marine Protected Areas to conserve cetacean populations in South America, a spatial analysis of the extent of cetacean distribution coverage by the existing MPAs is performed in Chapter 5. These data show that, on average, MPAs in South America cover less than 2% of the cetacean distribution, and that 19 species in this region have less than 1% of their distribution covered by protected areas. |
