The Costa Rica Dome : a study of physics, zooplankton and blue whales Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/3f4627639

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  • At the Costa Rica Dome (CRD), upwelling associated with cyclonic circulation and the presence of a shallow thermocline support a highly productive biological habitat, exploited by marine fauna at several trophic levels. During January 2008, a cruise to the CRD by the R/V Pacific Storm was conducted to relocate blue whales tagged off California in September 2007. In the process of relocating these whales, and others in the region, shipboard measurements of physical and biological parameters were taken with a goal of exploring how patterns of physical oceanography influence marine life in this area, particularly the distribution of blue whales and their prey. Conductivity-Temperature-Depth (CTD) casts were used to describe the physical habitat, while acoustic measurements and net tows were used to examine the distribution and behavior of zooplankton, and visual surveys and satellite tagging were used to examine habitat use by blue whales. CTD profiles showed a high level of physical variability in the water column. Tagged whales were selective in their movements for chlorophyll but not surface temperature. Prey and whales were both affected by subsurface temperature structure, not always reflected in satellite data. Acoustic backscatter data illustrated both layers and distinct, dense patches of zooplankton at various depths. These patches seemed most important to the distribution of blue whales with the total acoustic scattering from patches being a key feature in predicting blue whale proximity. Cluster analysis of acoustic regions revealed two types of patches, one of which was found only in the presence of blue whales. Collection of fecal samples from whales at the CRD confirmed their feeding in this region. Foraging during the winter reproductive season is not typical of baleen whales, but year-around forging may be an important element in the survival and recovery of blue whale populations. The data collected on this cruise demonstrate that the aggregation characteristics of prey are clearly important in determining the distribution of blue whales at the Costa Rica Dome during the northern hemisphere winter season.
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