Thesis

A multi-decadal study of seasonal abundance and timing changes in baleen whale observations from the Farallon Islands, CA

In the California Current System, baleen whales are used as a proxy for ecosystem health because they have been widely studied as a top predator. Oceanographic variability in the California Current System is dominated by three basin scale climate patterns, the Pacific Decadal Oscillation, the North Pacific Gyre Oscillation, and the Southern Oscillation which influence sea surface temperature, productivity, and upwelling. Humpback (Megaptera novaeangliae), blue (Balaenoptera musculus), and gray (Eschrichtius robustus) whales have been documented altering both timing of migration and switching prey when there are shifts in climate patterns. I hypothesized that both basin-scale climate and local oceanographic conditions would influence annual whale sightings and timing of arrival, peak, departure, and residency in central California. Using twenty-five years of weekly whale counts collected from Southeast Farallon Island, I developed two sets of regression models to test which environmental variables drive whale sightings and timings. I then developed a set of predictive models to determine if differences in sightings and timings could be predicted. I also compared sightings and timing to annual entanglement rates. There have been increased sightings in all species through time and variations are most commonly driven by sea surface temperature. Differences in timings are most influenced by El Nino events. Humpback entanglements are driven by whale arrival to central California, while, number of sightings drive gray whale entanglement rates. These models, and the continuation of long term monitoring, can be used to hopefully reduce the number of entanglements in central California.

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