Population structure and foraging ecology of southern right whales (Eubalaena australis): Insights from isotopic and genetic analyses

Ocean warming will undoubtedly affect the migratory patterns of many marine species, but specific changes can be predicted only where behavioral mechanisms guiding migration are understood. Southern right whales ( Eubalaena australis) show maternally inherited site fidelity to near-shore winter nursery grounds, but exactly where they feed in summer remains mysterious. Southern right whales are recovering from exploitation during the past two centuries, but their population numbers remain low at approximately 20% of pre exploitation estimates. However, their reproduction is influenced by reduction of food abundance linked to increased sea surface temperatures following El Nino events.;In this dissertation I show that genetic and isotopic signatures, analyzed together, indicate that maternal lineages are structured over an isotopic range, and that the isotope ratios from adult females are more similar than expected among individuals sharing the same mitochondrial haplotype. This pattern suggests a strong maternally directed site fidelity to summer feeding grounds. Such fidelity would be expected to limit the exploration of new feeding opportunities and might explain why this population shows increased rates of reproductive failure in years following sea surface temperature anomalies in the western South Atlantic. By comparing isotope ratios from skin samples with published and unpublished values of potential prey and other predators I have also discovered that southern right whales appear to have at least three different foraging strategies probably associated with different migratory patterns.;Additionally, I found significant genetic differentiation between live and dead animals, with an overrepresentation of dead calves within one of the two major phylogenetic clades known for this species. This overrepresentation is likely the outcome of a recent influx of migrants from populations where this clade is more abundant.;Finally, I present a study aimed at comparing mother and calf isotope ratios. I discovered interannual variability in the magnitude of nitrogen and carbon fractionation, which was interpreted as potential differences in the nutritional stress of the mother-calf pairs across years.;Here, I present the work conducted for my doctoral dissertation, which is aimed at increasing our understanding of the population structure, the foraging ecology and the migratory strategies of southern right whales.