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Habitat use of calling baleen whales in the southern California Current Ecosystem

  • Author(s): Vu, Elizabeth Tram Anh
  • Advisor(s): Hildebrand, John A
  • et al.
Abstract

The extent to which temporal, spatial, environmental, and physiological factors influence baleen whale acoustic occurrence was investigated in the southern California Current Ecosystem, a highly productive, upwelling-driven ecosystem that hosts a large abundance of top predators. By combining data sets from ten years of passive acoustic monitoring and concurrent environmental sampling, this dissertation presents detailed intra-annual and mesoscale spatial patterns previously unknown. Analyses of temporal acoustic patterns revealed different acoustic occupancy by three species: blue whale (Balaenoptera musculus), humpback whale (Megaptera novaeangliae), and fin whale (Balaenoptera physalus). The temporal separation between blue whale feeding and breeding call types showed a shift between behavioral states throughout the year. The temporal separation between blue and humpback whale reproductive calls showed different displays of reproductive calling behavior despite their overlapping migratory and seasonal reproductive cycles. Spatial patterns revealed different onshore and offshore occupancy, dependent on season, for each species. The reconciliation between acoustic and visual seasonal abundance demonstrated an increase in individual-level acoustic reproductive display during or approaching the mating season of each species. Analyses of habitat factors on call types from each species identified association of seasonality, bathymetry, sea surface temperature, and mixed layer depth with calling behavior. Generalized additive mixed models of acoustic calling revealed significant responses to seasonality and bathymetry at three different spatial scales, indicating the importance of these factors in explaining baleen whale distribution at broad scales. Lastly, a possible physiological driver of acoustic behavior was investigated by quantifying seasonal hormone concentrations in humpback whale blubber. The results of this research advance scientific understanding of yearlong acoustic cetacean occurrence in a productive oceanographic habitat and provide additional insight into the reproduction and migration of these species.

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